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Introduction Radio Frequency Identification (RFID) is a type of automatic identification technology that uses radio frequency to carry out wireless non-contact two-way data communication, with recording media (electronic tags or radio frequency cards) to read and write. The purpose is identifying the target and making data exchange. This is an extremely complex system, so it involves many parameters. Next, we will introduce several important parameters in detail. What is RFID? How RFID works? Catalog Introduction Ⅰ RFID Parameters Explained 1.1 Rx Sensitivity 1.2 SNR (Signal-to-Noise Ratio) 1.3 Tx Power 1.4 ACLR/ACPR 1.5 Modulation Spectrum/Switching Spectrum 1.6 SEM (Spectrum Emission Mask) 1.7 EVM (Error Vector Magnitude) 1.8 Interference Indicators 1.9 Dynamic Range, Temperature Compensation and Power Control Ⅱ FAQ Ⅰ RFID Parameters Explained Radio frequency identification involves many settings, that is, parameter selections. What are they? Here gives you the detailed descriptions as following mentioned. 1.1 Rx Sensitivity Receiving sensitivity is one of the most basic concepts, characterizes the lowest signal strength that the receiver can recognize without exceeding a certain bit error rate (BER), which is a general term that follows the definition of the circuit switched (CS) era. In most cases, BER or  Packet Error Rate (PER) will be used to examine the sensitivity. In the Long Term Evolution (LTE) era,  use throughput to define simply. LTE does not have a circuit-switched voice channel, but this is also a real evolution. Because for the first time we no longer use "standardization" such as 12.2kbps RMC (voice coding at 12.2kbps) to measure sensitivity, but the throughput that users can really feel.   1.2 SNR (Signal-to-Noise Ratio) When talking about sensitivity, we often refer to SNR (signal-to-noise ratio), we generally talk about the demodulation SNR of the receiver. We define it as the ability of the demodulator to not exceed a certain bit error rate, that is, SNR threshold for demodulation.So where do S and N come from? S means Signal, or useful signal; N means Noise. The useful signal is generally emitted by the communication system transmitter, and the source of noise is very wide. The most typical one is the famous -174dBm/Hz (natural noise). It is a quantity that has nothing to do with the type of communication system. In a sense, it is actually a noise power density related to temperature. In addition, how much bandwidth do we receive determine the noise, that is, the final noise power is integrated on the bandwidth by the noise power density. 1.3 Tx Power The importance of the transmission power is that the signal from the transmitter needs to pass through the fading of space to reach the receiver. So the higher the transmission power means the longer the communication distance.So should we consider SNR for our transmitted signal? For example, if the SNR of our transmitted signal is very poor, do we receive the same bad?This involves the concept just mentioned, the natural noise we assume that spatial fading has the same effect on both signal and noise (in fact, it is not, the signal can resist fading through coding but noise not) and it acts like an attenuator. For example, we assume spatial fading is -200dB, the transmitted signal bandwidth is 1Hz, the power is 50dBm, and the SNR is 50dB, then what is the SNR received by the receiver?The power of the signal received by the receiver is 50-200=-150Bm (bandwidth 1Hz), and the noise of the transmitter 50-50=0dBm through spatial fading, and the power reaching the receiver is 0-200=-200dBm (bandwidth 1Hz)? At this time, this part of the noise has already been "submerged" under the natural noise -174dBm/Hz. At this time, we only need to consider the "basic component" of -174dBm/Hz to calculate the noise to the receiver. Actually, this is applicable in most cases of communication systems.   1.4 ACLR/ACPR These parameters are explained together because they actually represent part of the "transmitter noise", but these noises are not in the transmitting channel, but the part that the transmitter leaks into the adjacent channels, which can be collectively referred to as "Leakage in the adjacent channel".ACLR and ACPR (actually one thing, but one is called in the terminal test, the other is called in the base station test), both are named after "Adjacent Channel". They both describe the machine pair interference from other equipment. And their power calculation of the interference signal is also based on a channel bandwidth. This measurement method considers the signal leaked by the transmitter and the interference to the equipment receiver of the same or similar standard-the interference signal falls into the receiver band with the same frequency and the same bandwidth. That is, form the same frequency interference to the signal received by the receiver.In LTE, the ACLR test has two settings: EUTRA and UTRA. The former describes the interference among the LTE systems, and the latter considers the interference of the LTE system to the UMTS system. So we can see that the measurement bandwidth of EUTRAACLR is the occupied bandwidth of LTE RB, and the measurement bandwidth of UTRA ACLR is the occupied bandwidth of UMTS signals (FDD system 3.84MHz, TDD system 1.28MHz). In other words, ACLR/ACPR describes a kind of "peer-to-peer" interference: the leakage of the transmitted signal interferes with the same or similar communication system.This definition is significant. For example, in the actual network, there are often signal leakage from neighboring cells from other or in the same region. In other words, the adjacent channel leakage of the system itself is typical for neighboring cells. Therefore, the process of network planning and optimization is actually the process of capacity maximization and interference minimization. In addition, from the other side of the system, the mobile phones of users in crowded people may also become a source of mutual interference.Similarly, in the evolution of communication systems, the goal has always been to "smooth transition", that is, to upgrade and transform existing networks into next-generation networks. Therefore, the coexistence of two or even three generations of systems should consider the interference between different systems. So the introduction of UTRA in LTE is to consider the radio frequency interference to the previous generation system UMTS.   1.5 Modulation Spectrum/Switching Spectrum In the GSM system, Modulation Spectrum and Switching Spectrum also play a similar role to adjacent channel leakage. The difference is that their measurement bandwidth is not the occupied bandwidth of the GSM signal. From a definition point of view, it can be considered that the modulation spectrum is a measure of the interference between synchronous systems, and the switching spectrum is a measure of the interference between asynchronous systems. In fact, if the signal is not gating, the switching spectrum will definitely cover the modulation spectrum.This involves another concept: in the GSM system, the cells are not synchronized, although it uses TDMA. In contrast, TD-SCDMA and later TD-LTE, the cells are synchronized.Because the cells are not synchronized, the power leakage of the rising edge/falling edge of the A cell may fall to the payload part of the B cell, so we use the handover spectrum to measure the interference of the transmitter to the adjacent channel in this state. And in the entire 577us GSM timeslot, the proportion of rising edge/falling edge is very small after all. What’s more, most of the time, the payload of two adjacent cells will overlap in time. In this case, the interference of the transmitter to the adjacent channel can be evaluated by referring to the modulation spectrum. Figure 1. RFID Chip 1.6 SEM (Spectrum Emission Mask) SEM is an in-band indicator, which is distinguished from spurious emission. The latter includes SEM, but the focus is on the spectrum leakage outside the working frequency band of the transmitter. In addition, its introduction is more based on the perspective of EMC (Electromagnetic Compatibility).SEM provides a spectrum template. When measuring the spectrum leakage in the transmitter band, see if there are any points that exceed the template limit. It can be said that it is related to ACLR, but it is not the same. ACLR considers the average power leaked into the adjacent channel, so it uses the channel bandwidth as the measurement bandwidth, and it reflects the "critical noise point" of the transmitter in the adjacent channel. Where SEM reflects the capture of over-standard points in adjacent frequency bands with a smaller measurement bandwidth (usually 100kHz to 1MHz), which reflects the noise-based spurious emission.If you scan the SEM with a spectrum analyzer, you can see that the spurious points on the adjacent channel will generally be larger than the ACLR average. Therefore, if the ACLR indicator itself has no margin, the SEM will easily exceed it. On the other hand, if the SEM exceeds the ACLR, it does not necessarily mean bad. For example, a common phenomenon is that there is LO spurious or a certain clock and LO modulation component (often very narrow bandwidth, similar to dot frequency) in the transmitter link, although ACLR is good, the SEM may exceed the standard.   1.7 EVM (Error Vector Magnitude) EVM is a vector, which means it has amplitude and angle. It measures the error between the actual signal and the ideal signal. This measurement can effectively express the "quality" of the transmitted signal. That is, the farther the point distance of the actual signal to the ideal signal, the greater the error and the greater the modulus of the EVM.Why is the SNR of the transmitted signal not so important? There are two reasons: the first is that it is often much higher than the SNR required for demodulation of the receiver. The second is the condition, that is, the worst case. The transmitter noise has already been submerged under the natural noise after a large spatial fading, and the useful signal is also attenuated to near the demodulation threshold of the receiver.But the "intrinsic SNR" of the transmitter needs to be considered in some cases, such as short-range wireless communication. Even without considering the spatial fading, demodulation of such high-order quadrature modulated signals alone already requires a high SNR. The worse the EVM, the worse the SNR and the higher the difficulty of demodulation. Engineers working on 802.11 systems often use EVM to measure Tx linearity. While engineers working on 3GPP systems, they like to use ACLR/ACPR/Spectrum to measure it.From the origin, 3GPP is the evolutionary path of cellular communication, and from the very beginning it has to pay attention to adjacent channel and alternative channel interference. In other words, interference is the number one obstacle that affects cellular communication rates. Therefore, 3GPP always aims at "minimizing interference" during its evolution, such as frequency hopping in the GSM era, spread spectrum in the UMTS era, and the RB concept in LTE era.The 802.11 system is an evolution of fixed wireless access. It follows the spirit of the TCP/IP protocol and aims at "service first". In 802.11, there use often time division or frequency hopping methods to achieve multi-user coexistence. The network layout is more flexible, and the channel width is also flexible and variable. In general, it is not sensitive to interference (or rather high tolerance).In layman's terms, the origin of cellular communication is to make phone calls, and users who cannot get through the phone will go to the telecommunications; while the origin of 802.11 is the local area network, you just wait at first when the network is not good.So this determines that the 3GPP series must take ACLR/ACPR and other "spectrum regeneration" performance as indicators, while the 802.11 series can adapt to the network environment at the expense of speed.Specifically, "Adapt to the network environment at the expense of speed" means that in the 802.11 series, different modulation orders are used to cope with the propagation conditions. When the receiver finds a signal difference, it immediately informs the opposite transmitter to reduce the modulation order. As mentioned earlier, SNR and EVM in an 802.11 system are highly correlated. To a large extent, a reduction in EVM can improve SNR. In this way, we have two ways to improve the receiving performance: one is to reduce the modulation order, thereby reducing the demodulation threshold; the other is to reduce the transmitter EVM, so that the signal SNR is improved.Because EVM is closely related to the demodulation effect of the receiver, EVM is used to measure the performance of the transmitter in the 802.11 system (similarly, in 3GPP, ACPR/ACLR is the index that mainly affects the network performance). In addition, the deterioration of EVM is mainly caused by non-linearity (for example, AM-AM distortion of PA), so EVM is usually used as a sign to measure the linear performance of the transmitter. Figure 2. RFID 1.7.1 Relations of EVM to ACPR / ACLR It is difficult to define the quantitative relationship between EVM and ACPR/ACLR. From the non-linearity of the amplifier, EVM and ACPR/ACLR should be positively correlated. That is, the AM-AM and AM-PM distortion of the amplifier will amplify the EVM, and also the ACPR/ACLR.However, EVM and ACPR/ACLR are not always positively correlated. For example, Clipping is commonly used in digital IF. It is to reduce the peak-to-average ratio (PAR) of the transmitted signal. The reduction of peak power can help reduce the ACPR/ACLR after passing through the PA. However, clipping will also damage the EVM. Because whether it is clipping (windowing) or using a filter, they all cause damage to the signal waveform, affecting the EVM. 1.7.2 Source Flow of PAR PAR (Peak-to-Average Ratio) is usually represented by a statistical function such as CCDF, and its curve represents the power (amplitude) value of the signal and its corresponding probability of occurrence. For example, if the average power of a certain signal is 10dBm, the statistical probability that it has a power exceeding 15dBm is 0.01%, and we can consider its PAR is 5dB.PAR is an important factor affecting transmitter spectrum regeneration (such as ACLP/ACPR/Modulation Spectrum) in modern communication systems. The peak power will push the amplifier into the nonlinear region and produce distortion. And the higher the peak power, the stronger the nonlinearity.In the GSM era, because of the constant envelope characteristic of GMSK modulation, PAR is 0. When designing GSM power amplifiers, we often push it to P1dB to get the maximum efficiency. After the introduction of EDGE, 8PSK modulation is no longer a constant envelope, so we tend to push the average output power of the amplifier to about 3dB below P1dB, because the PAR of the 8PSK signal is 3.21dB.In the UMTS era, whether WCDMA or CDMA, the PAR is much larger than that of EDGE. The reason is the correlation of the signals in the code division multiple access system. In other words,  when the signals of multiple code channels are superimposed in the time domain, the same phase may occur, and the power will show a peak at this time.The PNR of LTE is derived from the burstiness of the RB. OFDM modulation is based on the principle of dividing multi-user/multi-service data into blocks in both the time domain and the frequency domain, so that high power may appear in a certain "time block". LTE uplink transmission uses SC-FDMA. First, DFT extends the time domain signal to the frequency domain, which is equivalent to "smoothing" the burstiness in the time domain, thereby reducing PAR. Figure 3. RFID Applications 1.8 Interference Indicators The "interference index" here refers to the sensitivity test under various applied interferences in addition to the static sensitivity of the receiver. In fact, it is very interesting to study the origin of these test items.Our common interference indicators include Blocking, Desense, Channel Selectivity, etc. 1.8.1 Blocking Blocking is actually a very old RF indicator, as early as the invention of radar. The principle is to pour a large signal into the receiver (usually the first LNA that suffers the most), making the amplifier enter the nonlinear region or even saturate. At this time, on the one hand, the amplifier gain suddenly becomes smaller, and on the other hand, extremely strong nonlinearity occurs, so the function of amplifying useful signals cannot work normally.Another possible Blocking is actually done through the receiver's AGC. Large signals enter the receiver link, and the receiver AGC will reduce the gain to ensure dynamic range, but the useful signal level entering the receiver is very low. At this time, the gain is insufficient, and the amplitude of the useful signal entering the demodulator is insufficient.Blocking indicators are divided into in-band and out-of-band, mainly because the RF front-end generally has a band filter, which has an inhibitory effect on out-of-band blocking. However, the blocking signal is generally point frequency without modulation. In fact, point-frequency signals without modulation at all are rare in practice. In engineering, it is approximately point-frequency to replace various narrow-band interference signals.For solving Blocking, the key is RF. In other words, it is to expand the dynamic range of receiver. For out-of-band blocking, the rejection of the filter is also very important. 1.8.2 AM Suppression AM Suppression is a unique indicator of the GSM system. From the description point of view, the interference signal is a TDMA signal similar to the GSM signal, synchronized with the useful signal and has delay.This scenario simulates the signal of the neighboring cell in the GSM system. From the point of view that the frequency offset of the interference signal is greater than 6MHz (GSM bandwidth is 200kHz), this is a very typical neighboring cell signal configuration. So we can think that AM suppression is a reflection of the receiver's interference tolerance to neighboring cells in the actual work of the GSM system.Adjacent (Alternative) Channel Suppression (Selectivity)Here we collectively refer to it as "adjacent channel suppression". In the cellular system, in addition to the same-frequency cells, we must also consider adjacent-frequency cells in our networking. The reason can be found in the transmitter index ACLR/ACPR/Modulation Spectrum that we discussed before. Because of the transmitter's spectrum regeneration, there will be strong signals falling into adjacent frequencies (generally, the farther the frequency offset, the lower the level, so the adjacent channel is generally the most affected), and this kind of spectrum regeneration is actually related to the transmitted signal. That is, receivers of the same standard are likely to mistake this part of the regenerated spectrum as a useful signal for demodulation.For example, if two neighboring cells A and B happen to be neighboring frequency cells (such networking methods are generally avoided, here is just a assumption), when a terminal registered in cell A swims to the campus junction of two, but the signal strength of the two cells has not reached the handover threshold, the terminal still maintains cell connection with A, and the ACPR of the B cell base station transmitter is higher. So the terminal’s receiving frequency band has a higher ACPR component of B cell, which overlaps with the useful signal of cell A in frequency. Because the terminal is far away from the base station of cell A at this time, the received signal is weak. At this time, when the ACPR component of cell B enters the terminal receiver, it causes co-channel interference to the original useful signal.If we pay attention to the definition of the frequency offset of the adjacent channel selectivity, we will find that there is a difference between Adjacent and Alternative, which corresponds to the first and second adjacent channels of ACLR/ACPR. It can be seen that the "transmitter spectrum leakage (regeneration)" in the communication protocol and the "receiver adjacent channel selectivity" are actually defined in pairs. 1.8.3 Co-Channel Suppression (Selectivity) Co-frequency interference generally refers to the interference pattern between two cells.According to the networking principles we described earlier, the distance between two cells with the same frequency should be as far as possible. In addition, even if they are farther away, there will be signals leaking to each other, but the difference is in intensity. For the terminal, the signals of the two campuses can be regarded as "correct and useful signals" (of course, there is a set of access specifications on the protocol layer to prevent such false access). Frequency strength of both depends on its co-frequency selectivity. 1.8.4 Summery Blocking is big signal interferes with small signal, but the AM Suppression is small signal interferes with large signal.Single-tone Desense is a unique indicator of the CDMA system. It has a feature: the single-tone is an in-band signal and is very close to the useful signal. In this way, it is possible to generate two kinds of signals falling into the receiving frequency domain: First is due to near-end phase noise of the LO, the baseband signal formed by the mixing of the LO and the useful signal, and the signal formed by the mixing of the LO phase noise and the interference signal. Both will fall within the range of the receiver baseband filter, the former is a useful signal and the latter is interference. Second is due to the nonlinearity in the receiver system. The useful signal (with a certain bandwidth, such as 1.2288MHz CDMA signal) may produce intermodulation with the interference signal on the nonlinear device, falling in the receiving frequency domain and becoming interference.The origin of single-tone desense is that the CDMA system uses the same frequency band as the original analog communication system AMPS, and the two networks coexisted for a long time. So the CDMA system must consider the AMPS system's interference to itself.The explanation of Blocking in theory: the large signal entering the receiver causes the amplifier to enter the nonlinear region, and the actual gain becomes smaller (for useful signals).But it is difficult to explain two scenarios:Scenario 1: The pre-stage LNA has a linear gain of 18dB. When a large signal is injected to make it reach P1dB, the gain is 17dB. If no other influence is introduced (the default LNA NF, etc. have not changed), then the noise figure of the entire system is actually very limited. It is nothing more than the fact that the denominator of the latter-stage NF becomes a little smaller when it is included in the total NF, which has little effect on the sensitivity of the entire system.Scenario 2: The IIP3 of the previous LNA is very high, so it is not affected. The second level gain block is affected (the interference signal makes it reach near P1dB). In this case, the impact of the entire system NF is even smaller.Here is a point of view: the influence of Blocking may be divided into two parts. One part is that the gain mentioned in the textbook is compressed, and the other part is actually that after the amplifier enters the nonlinear region, the useful signal is distorted in this region. This kind of distortion may include two parts, one part is the spectrum regeneration (harmonic component) of the useful signal caused by pure amplifier nonlinearity, and the other part is the Cross Modulation of the large signal modulating the small signal.From this we also put forward another idea: if we want to simplify the Blocking test (3GPP requires frequency sweeping, which is very time-consuming), we may be able to select certain frequency points, which have the greatest impact on useful signal distortion when the Blocking signal appears.From an intuitive point of view, these frequency points may have: f0/N and f0*N (f0 is the useful signal frequency, and N is a natural number). The former is because the N-th harmonic component generated by the large signal in the nonlinear region is just superimposed on the useful signal frequency f0 to form direct interference, and the latter is superimposed on the N-th harmonic of the useful signal f0 and affects the output signal f0.According to Pascal's law, the waveform of the time domain signal is actually the sum of the domain fundamental frequency signal and each harmonic. When the power of the Nth harmonic in the frequency domain changes, the corresponding in the domain is the envelope change of the time domain signal (have distortion). Figure 4. RFID Readers   1.9 Dynamic Range, Temperature Compensation and Power Control These three indicators will only be shown when certain extreme tests are performed, but they themselves represent the most significant part of RF design. 1.9.1 Dynamic Range of the Transmitter The dynamic range of the transmitter characterizes the maximum and minimum transmission power without damaging other transmission indicators. This concept is very broad. If you look at the main effects, you can understand that the linearity of the transmitter is not compromised at the maximum transmission power, and the SNR of output signal is maintained at the minimum transmission power.Under the maximum transmit power, the output is often close to the nonlinear region of active devices at all levels (especially the final amplifier), and the nonlinearity that often occurs is spectral leakage and regeneration (ACLR/ACPR/SEM), modulation error (PhaseError/EVM). The most susceptible at this time is basically the linearity of the transmitter.Under the minimum transmit power, the useful signal output by the transmitter is close to the natural noise of the transmitter, and may even be submerged in the transmitter noise. At this time, what needs to be guaranteed is the SNR of the output signal. In other words, the lower the transmitter noise at the minimum transmit power, the better. 1.9.2 Dynamic Range of the Receiver The dynamic range of the receiver is actually related to the two indicators we talked about before, the first is the reference sensitivity, and the second is the receiver IIP3 (interference indicator).The reference sensitivity actually characterizes the minimum signal strength that the receiver can recognize. We mainly talk about the maximum receiving level of the receiver.It refers to the maximum signal that the receiver can receive without distortion. This distortion may occur at any stage of the receiver, from the previous LNA to the receiver ADC. For the front-level LNA, the only thing we can do is to increase IIP3 as much as possible so that it can withstand higher input power. For the subsequent step-by-step devices, the receiver uses AGC (automatic gain control) to ensure that the useful signal falls on the device within the input dynamic range. Simply put, there is a negative feedback loop: detect the received signal strength (too low/too high)-adjust the amplifier gain (up/down)-the amplifier output signal to ensure that it falls within the input dynamic range of the next stage device.Here we talk about an exception: the front-end LNA of most mobile phone receivers has AGC function. If you study their datasheet carefully, you will find that the front-end LNA provides several variable gain sections, and each gain section has its corresponding noise factor. Generally speaking, the higher the gain, the lower the noise factor. This is a simplified design. The design goal of the receiver RF link is to keep the useful signal input to the receiver ADC within the dynamic range and keep the SNR higher than the demodulation threshold (the SNR is not critical,  but "just enough"). Therefore, when the input signal is large, the front-stage LNA reduces gain, loss NF, and increases IIP3 at the same time. When the input signal is small, the front-stage LNA increases gain, reduces NF, and meanwhile reduces IIP3. Figure 5. RFID Discover 1.9.3 Temperature Compensation Generally speaking, we only have temperature compensation in the transmitter. Of course, the receiver performance is also affected by temperature. On the one hand, the receiver link gain decreases at high temperatures, and NF increases. On the other hand, at low temperatures, receiver link gain increases, and NF decreases. However, due to the small signal characteristics of the receiver, both gain and NF are within the range of system redundancy.It can also be subdivided into two parts: one part is the compensation for the power accuracy of the transmitted signal, and the other part is the compensation for the change in the transmitter gain with temperature.Transmitters of modern communication systems generally perform closed-loop power control (except for the slightly "old" GSM system and Bluetooth system). Therefore, the power accuracy of transmitters calibrated through production procedures actually depends on the accuracy of the power control loop. Generally speaking, the power control loop is a small signal loop, and the temperature stability is very high, so the demand for temperature compensation is not high, unless there are temperature-sensitive devices (such as amplifiers) on the power control loop.Temperature compensation for transmitter gain is more common, which has two common purposes:One is "visible", usually for systems without closed-loop power control (such as the aforementioned GSM and Bluetooth), this type of system usually does not require high output power accuracy, so the system can apply a temperature compensation curve (function) to keep the RF link gain within an interval. So that when the baseband IQ power is fixed and the temperature changes, the RF power output by the system can also be kept within a certain range.The other is "invisible", usually in a system with closed-loop power control. Although the RF output power of the antenna port is precisely controlled by the closed-loop power control, we need to keep the DAC output signal within a certain range (A common example is the need for digital predistortion (DPD) of the base station transmission system), then we need to control the gain of the entire RF link more accurately around a certain value.In the early stage of low accuracy and low cost accuracy requirements, temperature compensation attenuators are more common. Require higher accuracy requirements, the solution generally: temperature sensor + digital attenuator/amplifier + production calibration. 1.9.4 Power Control of the Receiver After talking about dynamic range and temperature compensation, let's talk about a related and very important index: power control.Transmitter power control is a necessary function in most communication systems. Commonly used in 3GPP, such as ILPC, OLPC, and CLPC. In addition, it must be tested in RF design.All transmitter power control purposes include two points: power consumption control and interference suppression.Let’s first talk about power consumption control: In mobile communications, in view of the changes in the distance between the two ends and the different levels of interference, for the transmitter, it is only necessary to maintain the signal strength enough for the receiver of the other party to demodulate accurately. If it is low, the communication quality is impaired, and if it is too high, the empty power consumption is meaningless. This is especially true for battery-powered terminals like mobile phones.Interference suppression is a more advanced requirement. In CDMA-type systems, because different users share the same carrier frequency (differentiated by orthogonal user codes), in the signal arriving at the receiver, user's signal is covered by the same frequency for other users. If the signal power of each user is high or low, the high-power user will drown out the low-power user’s signal. Therefore, the CDMA system adopts a power control method to control the power of different users reaching the receiver, and sends a power control command to each terminal to make the air interface power of each user the same. This kind of power control has two characteristics: the first is that the power control accuracy is very high (the interference tolerance is very low), and the second is that the power control cycle is very short (the channel may change quickly).In the LTE system, uplink power control also has the effect of interference suppression. Because LTE uplink is SC-FDMA, and multiple users also share carrier frequencies, which also interfere with each other, so the same air interface power.The GSM system also has power control. In GSM, we use power level to characterize the power control step length, each level is 1dB. It can be seen that GSM power control is relatively rough.Interference Limited SystemHere is a related concept: interference limited system. The CDMA system is a typical interference limited system. In theory, if each user code is completely orthogonal and can be completely distinguished by interleaving and de-interleaving, then the capacity of the CDMA system can be infinite. Because it can be used on limited frequency resources. The user code extended layer by layer distinguishes an infinite number of users. But in fact, since the user codes cannot be completely orthogonal, noise is inevitably introduced during multi-user signal demodulation. The more users there are, the higher the noise will be, until the noise exceeds the demodulation threshold. In other words, the capacity of the CDMA system is limited by interference (noise).The GSM system is not an interference limited system, but a time-domain and frequency-domain limited system. Its capacity is limited by frequency (a carrier frequency of 200kHz) and time domain resources (8 TDMAs can be shared on each carrier frequency user). Therefore, the power control requirements of the GSM system are not strict. 1.9.5 Transmitter Power Control and Transmitter RF Indicators Next, let's discuss the factors that may affect the transmitter power control in the RF design.For RF, if the power detection (feedback) loop design is correct, then we can do not much for the transmitter closed-loop power control (most of the work is done by the physical layer protocol algorithm), and the most important thing is the flatness in the transmitter band.Because the transmitter calibration can only be carried out on a limited number of frequency points, especially in the production test, the less frequency points the better. However, it is entirely possible for the transmitter to work on any carrier in the frequency band in practice. In a typical production calibration, we will calibrate the transmitter's frequency points to keep accuracy. So the closed-loop power control is correct at the calibrated frequency points. However, if the transmit power is not flat in the entire frequency band, some frequency points deviates greatly from the calibration frequency point. Therefore, the closed-loop power control with the calibration frequency point as a reference will have errors and even mistakes.   Ⅱ FAQ 1. What is RFID and how it works?RFID tags transmit data about an item through radio waves to the antenna/reader combination. ... The energy activates the chip, which modulates the energy with the desired information, and then transmits a signal back toward the antenna/reader. 2. What is RFID used for?RFID tags are a type of tracking system that uses radio frequency to search, identify, track, and communicate with items and people. Essentially, RFID tags are smart labels that can store a range of information from serial numbers, to a short description, and even pages of data. 3. Is RFID harmful to human?Electromagnetic fields generated by RFID devices—touted as a patient-safety technique to keep track of supplies, medical tests and samples, and people—could cause medical equipment to malfunction, according to a recent study of medical devices in Amsterdam published in the June 25 Journal of the American Medical. 4. What is RFID example?For example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly line, RFID-tagged pharmaceuticals can be tracked through warehouses, and implanting RFID microchips in livestock and pets enables positive identification of animals. 5. What are the components of RFID?Every RFID system consists of three components: a scanning antenna, a transceiver and a transponder. When the scanning antenna and transceiver are combined, they are referred to as an RFID reader or interrogator. 6. Who discovered RFID?Charles WaltonRFID was, however, officially invented in 1983 by Charles Walton when he filed the first patent with the word 'RFID'. NFC started making the headlines in 2002 and has since then continued to develop. 7. How is RFID made?The antenna can be made of etched copper, aluminum or conductive ink, while the chip and antenna are typically put on a substrate that is PET or paper. ... Usually, this inlay is inserted into a printable label to create an RFID transponder that can be affixed to a product. 8. Where did RFID come from?The First RFID PatentsMario W. Cardullo claims to have received the first U.S. patent for an active RFID tag with rewritable memory on January 23, 1973. That same year, Charles Walton, a California entrepreneur, received a patent for a passive transponder used to unlock a door without a key. 9. What is a RFID system?Radio Frequency Identification (RFID) refers to a wireless system comprised of two components: tags and readers. ... Passive RFID tags are powered by the reader and do not have a battery. Active RFID tags are powered by batteries. RFID tags can store a range of information from one serial number to several pages of data. 10. What are the three parameters that define an RFID system?Every RFID system consists of three components: a scanning antenna, a transceiver and a transponder. When the scanning antenna and transceiver are combined, they are referred to as an RFID reader or interrogator. 11. What are the basic criteria in RFID?Many large organizations and government agencies have mandated that their suppliers provide goods with RFID tags. These published mandates may specify tag type, frequency, amount of memory, read range, read rate and speed, and protocol. In addition, the mandates may specify how the goods should be tagged. 12. What is the maximum read range of RFID module?Maximum read distance of 1.5 meters (4 foot 11 inches) - usually under 1 meter (3 feet) and you can use a single or multi port reader plus custom antennas to extend the read range to longer tag read distances or a wider RFID read zone. 13. What is RFID in supply chain management?+RFID (Radio Frequency Identification) is a form of extremely low-power data communication between a RFID scanner and an RFID tag. ... The tags are placed on any number of items, ranging from individual parts to shipping labels. 14. How many bits does an RFID tag have?It depends on the vendor, the application and type of tag, but typically a tag carries no more than 2 kilobytes (KB) of data—enough to store some basic information about the item it is on. Simple “license plate” tags contain only a 96-bit or 128-bit serial number. 15. Does RFID reader store data?An RFID tag can store large amounts of data additionally to a unique identifier • Unique item identification is easier to implement with RFID than with barcodes. • Its ability to identify items individually rather than generically.

IntroductionAs we all know, Tire Pressure Sensor is a small programmable electronic device for driving safety. So what is the role of car tire pressure sensor? Just to prevent car accidents? Of course more than that, it can also extend the service life of the tires and even reduce the wear and tear of the suspension system. So this sensor should not be underestimated. Therefore, what exactly is the tire pressure sensor monitoring? How does it send signals to the vehicle controller? What is the difference between built-in and external sensor? Here gives a detailed introduction.TPMS Tire Pressure Monitoring Systems InstallationCatalogIntroductionⅠ Tire Pressure Sensor Working PrincipleⅡ Tire Pressure Sensor LocationⅢ Types of Tire Pressure Sensor Comparisons3.1 Original Second-generation Tire Pressure Sensors3.2 OEM Tire Pressure Sensors3.3 HUF TPMS Sensors3.4 Second-generation Tire Pressure SensorsⅣ Tire Pressure Sensor FaultsⅤ Tire Pressure Monitoring System ResetⅥ FAQⅠ Tire Pressure Sensor Working PrincipleThe tire pressure sensor signal is sent to the antenna receiver by sending a wireless signal of 433MHz or 355MHz, and the receiver sends the tire pressure data to the BCM (body control module) through the LIN (serial communication network), and finally compares with the BCM preset tire pressure data. If the tire pressure is too low, BCM will send a signal to the meter through the gateway via the high-speed CAN (serial communication protocol), showing the result. With the development of technology, the tire pressure sensor fully supports high-definition accurate monitoring of tire temperature, tire pressure and battery status to ensure driving safety at all times. The general-purpose tire pressure sensors on the market can replace all original sensors, copy the data of the original tire pressure sensors, and can repeat programming indefinitely.Figure 1. Tire Pressure Sensor Working PrincipleInstalling a tire pressure sensor is a direct type of tire pressure monitoring. Use the sensor installed in each tire to directly measure the tire pressure, then use the wireless transmitter to send the pressure information to the central receiver module, finally display the tire pressure data. When the tire pressure is too low or when there is a gas leak, the system will alarm automatically.In addition, there is also indirect tire pressure monitoring. Its working principle is: when the air pressure of a certain tire decreases, the weight of the vehicle will make the rolling radius of the tire smaller, causing its speed to be faster than other wheels. By comparing the rotational speed between the tires, in order to achieve the purpose of monitoring the tire pressure, the indirect tire alarm system actually relies on the tire's rolling radius to monitor the air pressure. Ⅱ Tire Pressure Sensor LocationThe tire pressure monitoring sensor is installed on the tire, usually at the valve position. The tire pressure monitoring display is usually placed on the center console. A lot of electronic devices are installed in the middle of the center console, which has a certain impact on radio frequency interference, especially the electronic eye. The tire pressure sensor can be divided into built-in type and external type according to the location where it is installed.The following is a display drawing of the location of the tire pressure sensor in a car:Figure 2. Tire Pressure Sensor Location Display Drawing1: Right-front wheel pressure monitoring sensor2: Central information display (can display tire inflation pressure info)3: Right-rear tire pressure monitoring sensor4: Remote control signal receiver5: Left-rear tire pressure monitoring sensor6: Combination instrument7: Dynamic stability control system8: Left-front tire pressure monitoring sensor🔺External Tire Pressure SensorFigure 3. External Tire Pressure SensorUsually, some of the original tire pressure sensors that the car is equipped with can display the current tire pressure, while others only give an alarm when the tire is out of air. For the external tire pressure sensor, the valve core has not played much role.The external tire pressure sensor is very simple to replace the battery. The battery can be opened by disassembling it with a wrench or other tools. The service life of the external battery is much shorter than that of the built-in battery due to structural design.🔺Built-in Tire Pressure SensorFigure 4. Built-in Tire Pressure SensorThe built-in sensor has obvious feature, that is, it can avoid being stolen and external interference, and it can be used for a longer time.But why can the original car tire pressure monitoring battery last for 8-10 years, while the latter can only be used for about 5 years? This is mainly due to the different working principles.In the original car, the tire pressure sensor is usually in a dormant state after the vehicle is stationary for 30 minutes. When the vehicle speed exceeds 30KM/hour, the sensor sends a signal to the receiver once a minute. The transmission frequency is about 433MHz, and the additional tire pressure sensor will emit a signal every 5 seconds or so when the tire rotates. So it is very power-consuming to use it.For driving safety, of course, the shorter the signal transmission interval, the better. However, tire leaks are generally slow. If it is a puncture, the tire pressure sensor will not play any role. Therefore, the sending interval of 1 minute is very reasonable, which can greatly improve the battery life.The principle is not complicated whether it is built-in or external sensors. The sensor sends the tire pressure data to the receiver via a wireless signal, and then displays it. Based on the above analysis of various tire pressure sensors, we can get such a result, that is, the stability of the original sensor is greater than that of the later installation. The built-in type is better than the external type in terms of use time and safety. Ⅲ Types of Tire Pressure Sensor Comparisons3.1 Original Second-generation Tire Pressure SensorsThe third-generation tire pressure of the original factory has been officially certified by Audi, with complete packaging and certificates. It is the most formal product. The service life of the qualified product of the original factory is more than six years.Advantages: High production standards. The various accessories used, including button batteries, have strict standards, and the accuracy of tire pressure data and transmission stability are very reliable.Disadvantages: After a lengthy supply chain, the cost rises. For example, a kind of tire pressure sensor is ordered from somewhere: the price is 400+, and the installation also requires modules, gas nozzles, and wiring harnesses, therefore, the price must be increased. 3.2 OEM Tire Pressure Sensors (off the official assembly line)Everyone knows that each OEM has its own dedicated supporting supplier, and the product will be installed and used in the car after very strict testing when it arrives at the OEM. This process will screen out a batch of products that do not meet the requirements of the OEM. , It may also be that the production date is too long. When the battery power does not meet the original factory requirements, it is treated as industrial waste.Advantages: Cheap priceDisadvantages: Sensor quality cannot be guaranteed. The production date is too long, the product does not have any packaging, the appearance and function (accuracy, sensitivity, etc.) cannot be guaranteed, and there is no after-sales service generally. 3.3 HUF TPMS SensorsThe comparison chart between HUF and the original tire pressure sensor shows that except for the different product codes, everything else is the same.Figure 5. Tire Pressure Sensor ComparisonAdvantages: The production standard is the same as the original product, except for the difference in marking and packaging. Because there is no Audi supply channel, the price is lower than the original product. Except that, the quality can be guaranteed by independent sellers.Disadvantages: Unofficial channels and no certificates. 3.4 Second-generation Tire Pressure SensorsThe sub-factory tire pressure sensor is a highly modeled product. Some small manufacturers have developed closely based on the original product. There are many brands and types of products. The appearance of this type of product is quite different from the above three types.Advantages: Cheap price.Disadvantages: The production standard is low, and the tire pressure data accuracy, transmission stability, and service life cannot be guaranteed. Although it can be used when installed, it is easy to have problems. Ⅳ Tire Pressure Sensor FaultsHow do I know if my tire pressure sensor is bad? The tire pressure sensor faults may be caused by the sensor running out of power, the sensor signal failure, and the sensor circuit failure. Due to different car usage conditions, you can check according to the following failure reasons:1) First of all, the air pressure is not high. If it is, the tire pressure needs to be reset; if not, it is a monitoring failure, but this possibility is small. Generally, the tire sensor is faulty, which will cause the brake system to turn the TPMS (tire pressure monitoring system) light on, and you can go to the repair shop to reset.Figure 6. Tire Pressure Sensor Light2) The Volkswagen series cars can supplement the standard air pressure, and then press the tire pressure monitoring button for a few seconds to reset. Other car models can use the decoder to reset or automatically reset after driving a certain distance when the standard air pressure is supplemented.3) The vehicle tire pressure is strictly the air pressure inside the tire, so the height of the tire has an important influence on the performance and power of the car. When you test a tire pressure sensor failure, you can check it.4) If the tire pressure sensor is out of power, it is easy for the tire pressure to be falsely reported. At the same time, the tire pressure value may be very unstable from high to low, and the brightness of the tire pressure display will decrease. When these problems occur, you can try to replace the tire pressure sensor battery to test.Over time the (Tire Pressure Monitoring System) TPMS sensors can go bad or the batteries can go dead. Here shows you how to replace TPMS sensors at home without a tire machine. Just look at the following video:How To Replace TPMS (Tire Pressure Monitoring System) Sensors? Ⅴ Tire Pressure Monitoring System Reset1) Press the button at the lower right corner of the multifunction steering wheel to calibrate the tire pressure monitoring system. You need to press the operating button to select "Vehicle Setting".2) Press the SEL/RESET button, the tire pressure monitoring system calibration will appear on the display.3) Press the SEL/RESET button, the display will switch to the personalized setting interface, and then select "Calibration".4) Press the SEL/RESET button, the "Calibration Start" message will appear on the multi-information display, and disappear after two seconds.Figure 7. Car Tire Pressure Sensors Ⅵ FAQ1. What does it mean when tire pressure sensor fault comes on?The “tire pressure sensor fault” message is an indication that there is a problem with the tire pressure monitoring system. ... If the tire is overinflated or underinflated, this could cause damage to the tire and/or hazardous driving conditions. 2. How much does it cost to fix a tire pressure sensor fault?Generally speaking, the TPMS sensor replacement cost is going to fall somewhere between $230 and $750 in most cases. And unlike some other auto repairs, it's the parts, not the labor, that are going to get you. TPMS sensors can cost anywhere from $180 to $680 alone. 3. Can you drive with a bad tire pressure sensor?No, driving with the TPMS Light on is not safe. It means one of your tires is underinflated or overinflated. ... This can cause undue wear on the tire, potentially lead to a tire failure, and cause a blowout dangerous to you and other drivers on the road. 4. How do I test my TPMS sensor?It is important check the TPMS system before working on a customer's vehicle. Using a TPMS diagnostic tool, select the vehicle's make, model and year manually – or for faster service, scan the vehicle's VIN barcode located on the placard on the vehicle doorjamb to read the sensor information. 5. How long do tire pressure sensors last?The lithium ion batteries inside tire pressure sensors may last anywhere from five to 10 years. Five to six years is a more typical lifespan for older TPMS sensors. The lithium ion batteries inside TPMS sensors may last anywhere from five to 10 years. 6. Can you drive without tire sensors?Yes you can. If you are in canada, there is no law about tpms (tire pressure monitoring system), so there is no problem to drive without it. In USA, this is forbidden. Over this, you will have a light on in your dash if you wheel don't have sensor, but no other issue. 7. How much should it cost to replace a tire sensor?The service kit costs $5-$10 per wheel on most vehicles. A special TPMS tool and additional time are also needed to check and reset the sensor system. In the event pressure sensors need to be replaced, the cost ranges from $50-$250 each depending on vehicle type. 8. How do you fix a tire pressure sensor?Press the TPMS reset button and hold it until the light blinks three times, then release it. Start the car and let it run for 20 minutes to reset the sensor. You'll usually find the tire pressure monitor reset button beneath the steering wheel. Check your user's manual if you're having trouble locating it. 9. How do I know if my tire pressure sensor is bad?Drive for a little bit. The light should go off as the sensor reads the new pressure levels. If the light stays on, you should have us check your tires for a leak or another issue that may not be immediately visible. If the tire pressure is stable, then it could be a bad sensor. 10. Why do tire pressure sensors fail?Some tire pressure sensors have been known to fail as a result of corrosion. ... This can result in valve stems breaking off or cracking, causing the tire to go flat. Other reasons for failure include wiring faults, issues with keyless entry systems, and TPMS module failure, however these are all far less common faults. 11. Can you turn off tire pressure sensor?The U.S. Department of Transportation has mandated that all vehicles manufactured after 2008 include a tire pressure monitoring system (TPMS). Although you cannot disable the TPMS in a General Motors (GM) vehicle, you can reset the system if you recently checked your tires and inflated them properly. 12. Can I replace just one TPMS sensor?You can replace just one sensor. However, when you replace a TPMS sensor you have to "register" it on the vehicle. That is, the vehicle ECU has to be programmed to know that it has a new sensor with a new ID. 13. Is it worth it to replace TPMS sensors?The only time when the TPMS sensor replacement cost might not be worth it is when your car isn't worth much at all. If you have an older car that isn't worth a whole lot of money, paying to have bad TPMS sensors replaced might not be in your best interests. 14. Can you replace battery in TPMS sensor?Most TPMS sensors run on batteries that are built into the sensor and these batteries are not replaceable. The life expectancy of the lithium ion batteries in a TPMS sensor is anywhere from 5-10 years. ... If one of your TPMS sensors fails and needs replacement, you can replace it individually. 15. How do I get the TPMS light to go off?Drive the car at 50 mph for about 10 minutes.This should reset the sensor, and the next time you start the car the TPMS light should be off. Without starting the car, turn the key to the “On” position. Press the TPMS reset button and hold it until the light blinks three times, then release it.

IntroductionWith the advancement of automobile technology, an increasing number of cars are equipped with car tire pressure monitoring systems, which provide us with a quick and real-time understanding of the car tire pressure, and we no longer have to worry about insufficient and excessive tire pressure before driving, and the car tire pressure monitoring system has brought great convenience to our car. Currently, most car tires are equipped with pressure sensors to detect pressure changes in order to ensure the safety of car driving. According to relevant statistics, tire pressure reaches a reasonable value, which can not only improve driving safety but also reduce fuel consumption. So, how does a car tire pressure sensor work? This article will introduce in detail.Video: Tire Pressure Sensors CatalogIntroductionⅠ Principles of Tire Pressure Sensors in AutomobilesⅡ Design Background of TPMSⅢ Tire Pressure Sensors in a Tire Pressure Monitoring SystemⅣ Details of Tire Pressure Sensors in Direct Tire Pressure Monitoring SystemⅤ SummaryⅥ Frequently Asked Questions about Tire Pressure Sensors Ⅰ Principles of Tire Pressure Sensors in Automobiles1.Strain Sensors in AutomobilesThe principle of a strain sensor is primarily based on the resistive strain effect,when the conductor undergoes mechanical deformation due to external action, a corresponding change in resistance value occurs. Calculate the required pressure by first calculating the magnitude of strain using the relationship between the change in resistance value and the change in output electrical signal. The strain gauge pressure sensor is primarily used to measure the dynamic or static pressure of a flowing medium, such as the inlet and outlet gas or liquid pressure of power pipeline equipment, engine pressure, internal combustion engine pipeline pressure, and so on.The most widely used strain gauge is the paste strain gauge (strain gauge). Its main disadvantages are small output signal, narrow linear range, and poor dynamic response (see resistance strain gauge, semiconductor strain gauge). However, due to the small size of strain gauge, many specifications of commercial strain gauge can be selected, and the form of elastic sensor can be flexibly designed to adapt to various applications, strain type pressure sensor made by strain gauge is still widely used. According to the different structure of elastic sensor, strain type pressure sensor can be roughly divided into strain tube type, diaphragm type, strain beam type and combined type.Figure:Strain Sensors in Automobiles 2.Piezoresistive Pressure Sensors in AutomobilesThe piezoresistive pressure sensor's pressure sensitive element is a piezoresistive element that operates on the piezoresistive effect. The term "piezoresistive element" actually refers to the diffusion resistance created by integrated circuit technology on a semiconductor substrate. When subjected to external force, its resistance changes due to resistivity change. During normal operation, diffusion resistors must be attached to elastic elements, and monocrystalline silicon diaphragms are commonly used.The piezoresistive pressure sensor's main advantages are its small size, relatively simple structure, good dynamic response, high sensitivity, and ability to measure micro pressures of more than ten Pascals. It is a relatively ideal one, and it is currently being developed and applied at a rapid pace. Sensor of pressure. Non-linearity and temperature affect the measurement accuracy of this sensor, affecting the size of the piezoresistive coefficient. Microprocessors are used in today's intelligent piezoresistive pressure sensor to compensate for nonlinearity and temperature. It integrates the sensor and computer on the same silicon chip using large-scale integrated circuit technology, and it has functions such as signal detection, processing, and memory. As a result, the sensor's stability and measurement accuracy are greatly improved.Figure:Piezoresistive Pressure Sensor 3.Other Automotive Pressure SensorsFurthermore, differential transformer type pressure sensors (LVDT) and surface elastic wave pressure sensors are available (SAW). SAW type pressure sensors have small size, light weight, low power consumption, high reliability, high sensitivity, high resolution, digital output, and so on. LVDT type pressure sensors have larger output, easy to digital output, but poor anti-interference. It is used to detect the pressure of an automobile suction valve and can operate reliably in high temperatures. Ⅱ Design Background of TPMSThe tire pressure influences both the car's excellent performance and the length of the tire's service life. According to SAE (Society of Automotive Engineers) data, there are more than 260,000 traffic accidents caused by tire failure in the United States each year, with flat tires accounting for 70% of highway accidents. Furthermore, natural tire leakage or under-inflation is the leading cause of tire failure. Every year, approximately 75% of tire failures occur. The data also shows that in high-speed driving, punctures caused by tire failure are a major cause of traffic accidents.Flat tires, the unseen killer, have caused numerous human tragedies and incalculable economic losses to the country and businesses. As a result, in order to reduce the number of traffic accidents caused by flat tires, the US federal government has mandated that automakers accelerate the development of TPMS ( Tire Pressure Monitoring System).Figure:Tire Pressure Monitoring System Ⅲ Tire Pressure Sensors in a Tire Pressure Monitoring SystemThere are two main tire pressure monitoring system solutions: direct system and indirect system.The direct tire pressure monitoring system measures tire pressure directly using the pressure sensor installed in each tire and displays and monitors the tire pressure. The system will automatically alert if the tire pressure is too low or if there is a leak.To monitor tire pressure, the indirect tire pressure monitoring system compares the speed difference between tires using the wheel speed sensor of the automobile abs system.The main disadvantages of this type of system are as follows: 1. The accurate instantaneous air pressure value of each tire cannot be displayed; 2. It is not possible to alarm when the pressure of the same axle, same side wheel, or all tires drops at the same time; and 3. Factors such as vehicle speed and detection accuracy cannot be taken into account simultaneously.Figure:Tire Pressure Sensors in a TPMS Ⅳ Details of Tire Pressure Sensors in Direct Tire Pressure Monitoring SystemThere are two types of direct tire pressure monitoring systems: active and passive.The active system makes capacitive or piezoresistive pressure sensors on silicon using mems technology. Each rim has a pressure sensor, and the signal is transmitted via radio frequency. It is set up in the wireless cab. The pressure sensitive signal is received by the receiving device, which then displays the current tire pressure after some signal processing.The advantage of active technology is that it is relatively mature, and the modules developed can be applied to tires of various brands, but the disadvantages are also more noticeable. Its induction module requires battery power, posing a problem with system service life.The passive tire pressure monitoring system's sensor is based on surface acoustic waves. A radio frequency electric field is used to generate a surface acoustic wave in this sensor. The surface acoustic wave changes as it passes through the surface of the piezoelectric substrate material. The change in the surface acoustic wave can indicate tire pressure. Although this technology does not require battery power, it does necessitate the integration of the transponder into the tire, and it can only be implemented if tire manufacturers agree on a common standard. The tire pressure monitoring system must detect abnormal tire pressure conditions, and it can only do so with high resolution and accuracy. Battery life is limited, and capacity is affected by temperature as well. It is best for the sensor to perform passive detection in order to improve system reliability. According to studies, the information collected by tire pressure sensors can be used to monitor vehicle suspension failures and correct navigation systems. As a result, the future automotive pressure sensor should be a passive intelligent sensor with multiple functions. Ⅴ SummaryIn recent years, automotive sensors have been the fastest growing and most widely used sensor category. The growth of the automotive industry encourages the rapid development of automotive pressure sensors. Sensor performance is improving as a result of advances in manufacturing and process technology, and tire pressure monitoring is becoming increasingly important. Ⅵ Frequently Asked Questions about Tire Pressure Sensors1.When should a tire pressure sensor be replaced?TPMS sensors are designed to last for many years.5-10 years is a likely lifespan. Given their cost, most drivers will be inclined to replace TPMS sensors on an “as needed” basis.In other words, only once their batteries have expired, or other TPMS components have failed. 2.Is it safe to drive with tire pressure sensor fault?No, driving with the TPMS Light on is not safe. It means one of your tires is underinflated or overinflated. This can cause undue wear on the tire, potentially lead to a tire failure, and cause a blowout dangerous to you and other drivers on the road. 3.How much does it cost to replace a tire pressure sensor?The average cost for TPMS sensor replacement is between $207 and $257. Labor costs are estimated between $53 and $67 while parts are priced between $154 and $190. This range does not include taxes and fees, and does not factor in your specific vehicle or unique location. Related repairs may also be needed. 4.How do you fix a tire pressure sensor?Without starting the car, turn the key to the “On” position. Press the TPMS reset button and hold it until the light blinks three times, then release it. Start the car and let it run for 20 minutes to reset the sensor. You'll usually find the tire pressure monitor reset button beneath the steering wheel. 5.How do I know if my tire pressure sensor is bad?A small light illuminates at the dashboard's display panel whenever there is a problem with the tire pressure sensors. It appears as a vivid yellow exclamation point inside of a U symbol; you'd be easily able to spot it. As soon as it turns on, the driver must check the tire for less or no air.  

IntroductionIn the lighting industry, people often have a misunderstanding about dimming LED lights. And the reality is that the application of LED light source dimming technology in engineering is often unsatisfactory. Why is this the case? Is the LED light source dimming technology immature, or the technology is difficult to master? So this article analyzes the LED dimmer to help readers to fully understand and master it.Dimming all kinds of LEDs?CatalogIntroductionⅠ Dimming LED Lights1.1 What is Dimming?1.2 LED Dimming Circuit Example1.3 LED Dimming Using SCRⅡ Dimming LED Using PWM2.1 LED Dimming Current2.2 LED PWM Dimmer2.3 LED PWM Dimming Advantages2.4 LED PWM Dimming Problems2.5 DALI PWM Dimmer IntroductionⅢ Main LED Dimmers ComparisonsⅠ Dimming LED Lights1.1 What is Dimming?LED dimmer switch is an electrical device that changes the luminous flux of the light source in the lighting device and adjusts the illuminance level. The purpose of the dimmer is to adjust the different brightness of the light. By reducing or increasing the rms voltage, the light output of different intensities produced by the average power lamp is promoted. Although variable voltage devices can be used for various purposes, this regulation is aimed at controlling lighting. Regarding the LED dimmer switch, we must first understand the volt-ampere characteristics of the LED. That is, the characteristics of the current flowing through the LED PN junction with voltage. Generally, the reverse characteristic curve changes steeply. When the voltage exceeds a certain threshold, the current will rise exponentially, thereby breaking down the LED PN junction. The forward voltage of the LED is also determined by its forward current. It can be seen from the figure that the change of the forward current will cause the corresponding change of the forward voltage, to be precise, the decrease of the forward current will also cause the decrease of the forward voltage. Therefore, when the current is lowered, the voltage of the LED will also decrease, which will change the relationship between the power supply voltage and the load voltage.Figure 1. Diode Volt-Ampere Characteristics CurveTherefore, from the volt-ampere characteristics of the LED, we can know that the dimming of the light source cannot be achieved simply by reducing the input voltage or input current of the LED. In addition, the waveform of the sine wave of the LED is different from the waveform of the incandescent lamp, so it cannot simply change its conduction angle to achieve the purpose of dimming.LED dimming methods can be divided into analog dimming and digital dimming. Analog dimming is to achieve dimming by changing the current in the LED loop. The power supply voltage remains unchanged, and the current in the loop is changed by changing the resistance value to achieve the effect of changing the brightness of the LED. Many analog dimming is an extension of this method. Its advantage is that the current can be continuous, but the range of adjustable current is often limited by hardware, and there are few adjustment gears. This method is not ideal for high-precision lighting equipment.Digital dimming, also known as PWM (Pulse Width Modulation) dimming, uses PWM waves to turn on and off the LED to change the on-time of the forward current to achieve the effect of brightness adjustment. This method is based on the fact that the human eye is not sensitive enough to the brightness flicker. If the frequency of brightness and darkness exceeds 100Hz, the average brightness is seen by the human eye, not the LED flickering. PWM adjusts the brightness by adjusting the ratio of light and dark time. In a PWM cycle, because the perceived brightness of human eyes to flicker is a cumulative process, that is, the brighter time accounts for the greater the proportion of the entire cycle. The longer the time, the brighter the human eye feels.1.2 LED Dimming Circuit ExampleFor example, in an LED lamp with an input of 24V, 8 1W high-power LEDs are connected in series. When the forward current is 350mA, the forward voltage of each LED is 3.3V, then 8 pieces in series is 26.4V, so a constant current source greater than 24V should be used. However, in order to dimming, the current is reduced to 100mA. At this time, the forward voltage is only 2.8V, and 8 pieces are connected in series to 22.4V. The load voltage becomes lower than the input voltage, so that a constant current source larger than 24V cannot work, and finally the LED will flicker.In this case, you may choose a step-down (wide voltage) constant current source, such as a 10V-30V constant current source for dimming. However, if this type is adjusted to a low forward voltage, the LED load current will also become very low. So the step-down ratio is very large, beyond the normal working range of constant current source, which will make LED unable to work and cause flicker. In addition, LED works at low brightness for a long time, which will reduce its efficiency and increase the temperature rise. Because the efficiency of the step-down constant current source is related to the voltage ratio, the larger the voltage drop ratio, the lower the efficiency. And greater power loss on the chip will damage the life of the constant current source and the LED light source.1.3 LED Dimming Using SCROrdinary incandescent lamps and halogen lamps usually use thyristors for dimming. Because they are pure resistance devices, and do not require the input voltage to be a sine wave. Their current waveform is always the same as the voltage waveform, no matter how the voltage waveform deviates from the sine wave, changing the effective value of the input voltage will dim the LED light .However, the adjustment of LED light source by thyristor dimming will cause unexpected problems, that is, the LC filter at the input will cause the thyristor to oscillate. This oscillation is indifferent to the incandescent lamp, human eyes can't see it at all because of thermal inertia. However, this dimming method will cause the driving power of LED produce audio noise and flicker. It will also destroy the waveform of the sine wave, thereby reducing its power factor value (usually lower than 0.5), which greatly reduces the system efficiency of the LED. Moreover, the thyristor dimming waveform increases the harmonic coefficient, and the non-sinusoidal waveform will cause serious electromagnetic interference on the line to pollute the power grid.Ⅱ Dimming LED Using PWM2.1 LED Dimming CurrentHere, you may ask: Lower voltage or current or thyristor dimming methods are not suitable for LED light source dimming, so what is the most suitable method?Is it an analog (0-10V) dimming method? May be not. Analog dimming faces a severe challenge, which is the output current accuracy. Almost every LED driver needs some kind of series resistance to distinguish the current, and the tolerance, offset and delay in the analog (0-10V) dimming drive cause a relatively fixed error, which will reduce the accuracy of the output current, and the final output current cannot be specified, controlled or guaranteed. Therefore, to ensure the dimming effect of the LED light source, one of the important rules is to reduce the output current error and improve the current accuracy in a closed loop system.2.2 LED PWM DimmerThe PWM dimming method can solve the above problems very well. Because diode characteristics, LED can realize fast switching, and its allowable switching speed can be as high as microseconds or more. Therefore, as long as the power supply is changed to a pulse constant current source, the brightness can be changed by PWM. This PWM dimming. This method is like a sluice that opens and closes in microseconds or more. The switching frequency of it is so fast that humans can’t recognize the state of its opening with the naked eye. As a result, people can only identify the speed of its switching frequency by the amount of water downstream. In addition, because the sluice changes the duty cycle of the output water flow (effective water flow), it does not change the instantaneous water pressure and flow rate, so the opening and closing action of the sluice gate will not affect the hydropower generation. The amount of water flowing down and power generation are just changed. Therefore, the PWM dimming method does not change the instantaneous voltage and current of the input LED PN junction, but changes the duty cycle of the output current to change LED brightness.2.3 LED PWM Dimming Advantages1) There will not be any LED chromatogram shift, because the LED always works between the full amplitude current and 0.2) It has a very high dimming accuracy, because the pulse waveform can be controlled to a high precision.3) Even if the light is dimmed in a wide range, there will be no flicker. Because it will not change the working conditions of the constant current source (boost ratio or step-down ratio), problems such as overheating are less to occur.4) It can be combined with digital (DALI/DSI/DMX 512) control technology for control, because the digital control signal can easily be transformed into a PWM signal.2.4 LED PWM Dimming Problems1) Because the LED is in a fast switching state, if the working frequency is very low, the human eye will feel flicker. In order to make full use of the residual visual phenomenon of the human eyes, its operating frequency should be higher than 100Hz, preferably 200Hz.2) Eliminate the howling caused by dimming. Although the human eye can't detect it above 200Hz, it is within the range of human hearing until 20kHz. At this time, it is possible to hear the slightest voice. There are two ways to solve this problem: One is to increase the switching frequency above 20kHz, out of the range of human hearing, another is to find out the sound-producing device and deal with it.At present, some manufacturers have solved the above problems well. A good LED light source dimming technology needs a good LED control signal technology to match and cooperate in order to become an effective, stable and reliable system. For example, the LED PWM dimming method has the advantage that the digital control signal can easily be converted into a PWM signal. At the same time, in the digital control signal of lighting, DALI (Digital Addressable Lighting Interface) has the unparalleled superiority of other lighting digital control methods, and it is also the mainstream of the current digital control application in the lighting industry. Therefore, the matching of PWM dimming mode and DALI takes into account their respective advantages, where PWM dimming technology solves the final dimming problem of LED light sources, and DALI solves the control, feedback and networking of each LED light.Figure 2. LED PWM Dimming Circuit2.5 DALI PWM Dimmer IntroductionThe biggest feature of DALI technology is that each lamp has an independent address. Through the DALI system software, a single lamp or any lamp set can be accurately dimmed and switched, regardless of whether the lamps are on strong current loop or not. That is to say, the lighting control has nothing to do with the strong current circuit. The DALI system software can independently address single or multiple lamps on the same strong current circuit or different circuits, to achieve individual control and arbitrary grouping set. This concept brings great flexibility to lighting control, which can meet different LED lighting requirements. Even after installation, they can still modify the control requirements at will, without having to do anything to the wiring.The following are the application advantages of PWM dimming method combined with DALI.1) The design is simple and easy to implement.In the design, as long as they are connected to each other through the digital signal interface, they are connected in parallel to the 2-core control line. All design process can be programmed by computer software during installation and debugging, which not only saves design costs, but also improve working efficiency.2) Simple and economical installationThe DALI control line has no special requirements for the wire and no polarity requirements during installation. It only requires the main power line to be separated from the control line. The control line does not need to be shielded. When the current on the control line is 250mA and the line is 300 meters long, the drop does not exceed 2V. The control line and the power line can be parallel, no need to bury the line separately. The compact design of the control components does not require a special control cabinet, so installation is simple and economical.3) Simple and convenient operationThe PWM LED driver with DALI control can automatically handle filament preheating, ignition, dimming, switching, fault detection and other functions. The user interface is very friendly. Users can operate and control without deep understanding, such as sending a change. According to the command of the scene, each relevant LED driver calculates the dimming rate according to the difference between the current brightness and the required installation brightness to achieve that all the LED light sources are synchronized to the required scene brightness.4) Accurate and reliable controlDALI is a digital signal, which is different from an analog signal. The signal of 1010 can realize disturbance-free control, and will not distort the control signal due to long-distance voltage drop. Therefore, even if the DALI digital signal control line and the strong wire are in the same line and tube, it will not be disturbed. The DALI signal is two-way transmission, which not only transmits control commands forward, but also feeds back the information of the LED driver's status, fault information, switch, and actual brightness value to the system.5) Wide range of applicationsNowadays, DALI interface is not only used for fluorescent lamp ballast dimming, various electronic transformers for halogen lamps, electronic ballasts for gas discharge lamps. DALI technology also employed in wide range of LED light control makes it more and more widely. Ⅲ Main LED Dimmers Comparisons1) SCR DimmingFigure 3. SCR Dimming Circuit Diagram✅Advantages: It has the advantages of high adjustment accuracy, small size, light weight, easy remote control, etc., which occupies a leading position in the market.❎Disadvantages: The front-cut LED dimmer is prone to generate noise, so it is not recommended for high-demand occasions. The minimum load will vary depending on the LED dimmer and light source. It is necessary to consider derating to adapt to the spike caused by the driver. The typical derating percentage should be 25%-30% of the maximum rated load of the dimmer circuit. 2) CMOS DimmingFigure 4. CMOS Dimming Circuit Diagram✅Advantages: There is no minimum load requirement, so that better performance can be achieved on a single LED lighting device or a very small load.❎Disadvantages: High cost, complicated dimming circuits, lack of high-power products, and poor stability. 3) 0-10V DimmingFigure 5. 0-10V Dimming Circuit Diagram✅Advantages: Simple application, good compatibility, high precision, better dimming effect than phase-cut dimming.❎Disadvantages: Need to add additional control lines and controllers. The dimming effect is related to the wire diameter, cable material, power current, and power supply quantity of 0-10V dimming. 4) DALI DimmingFigure 6. DALI Dimming Circuit Diagram✅Advantages: Accurate and smooth dimming, two-way communication, and strong anti-interference ability, mainly used in single lamp control.❎Disadvantages: Like 0-10V products, additional control circuits and controllers need to be added. 5) DMX512 DimmingFigure 7. DMX512 Dimming Circuit Diagram✅Advantages: Powerful control functions bring rich lighting effects to architectural lighting, night lighting, studios and variety shows.❎Disadvantages: Special wiring layout and types are required, and certain programming is required to set the basic colors and scenes, which is more costly for later maintenance. The ideal transmission distance of DMX signal is less than 200 meters. And meanwhile, in actual use, the signal is greatly interfered by the outside world. 6) SLC and Ready2mains DimmingFigure 8. LED Dimming via Ready2mains✅Advantages: The digital dimming signal is transmitted through the AC wire, without additional signal wires and wiring. Digital signal transmission has good anti-interference performance and excellent dimming effect.❎Disadvantages: At present, there are relatively few products using this type of digital dimming technology, so there are relatively few compatible products. Frequently Asked Questions about LED Dimmer1. What are LED dimmers?An LED dimmer is the term for a device that performs a dimming control operation within such an LED lighting device. LEDs react instantaneously to alterations in power input, making solid state lighting especially suitable for dimming scenarios. 2. Why do my LED dimmer lights flicker?LED bulb flickering can be traced in almost every instance to a non-compatible dimmer switch in the lighting circuit. ... LED bulbs don't have glowing filaments. When the dimmer switch goes off and on many times per second, the LED bulb becomes a flickering strobe light. 3. Do you need a special dimmer for LED lights?Use an LED Dimmer switchA standard dimmer switch cannot be used with an LED light as you will never be able to dim the LED light either completely or not very well. LED lights need their own special electronic dimmer switch to have a fully functioning and dimming light. 4. How do LED dimmer switches work?In the case of PWM, dimmable LEDs work by creating a dimming effect. Unlike traditional lighting such as incandescent, dimmable LED bulbs don't rely on voltage to dictate their level of brightness. Instead, they essentially rely on a cycle of being on and off. 5. What is the best dimmer switch for LED lights?Best Overall: Lutron Toggler Single-Pole/3-Way Light Dimmer.Best Budget: GE Slide Dimmer Rocker Wall Switch, Single Pole.Best Smart: Kasa Smart Dimmer Switch HS220.Best for Bedrooms: Lutron Maestro LED+ Dimmer Switch, Single-Pole or Multi-Location.Best for LED: Lutron Diva LED+ Dimmer Switch, Single-Pole or 3-Way.

IntroductionA three-phase circuit consists of a three-phase source, a three-phase load, and a three-phase transmission line. The most basic characteristic of this circuit is that it has one or more groups of power supplies. Each group consists of three sinusoidal power supplies with the same amplitude, the same frequency, 120° phase difference, and the power supply and the load are connected in a specific way. Three-phase circuits are widely used in power systems such as power generation, transmission, distribution, and high-power electrical equipment.What does 3 phase mean?CatalogIntroductionⅠ Three-phase Circuit Basics1.1 Three-phase Circuit Characterized1.2 Three-phase Circuit Terms1.3 Three-phase Voltage & Current1.4 Three-phase Circuit AdvantagesⅡ Symmetrical vs Asymmetrical2.1 Symmetrical Three-phase Circuit2.2 Three-phase AsymmetryⅢ Power in Three Phase Circuit FormulasⅣ Frequently Asked Questions about Three-phase CircuitⅠ Three-phase Circuit BasicsThe three phases could be supplied over six wires, with two wires reserved for the exclusive use of each phase. However, they are generally supplied over only three wires, and the phase or line voltages are the voltages between the three possible pairs of wires. The phase or line currents are the currents in each wire. Voltages and currents are usually expressed as rms or effective values, as in single-phase analysis.1.1 Three-phase Circuit CharacterizedSpecial power supplySpecial loadSpecial connectionSpecial solution1.2 Three-phase Circuit Terms1) End wire (fire wire)2) Neutral line3) Line current4) Line voltage5) Phase current6) Phase voltage7) Three-phase three-wire system and three-phase four-wire system1.3 Three-phase Voltage & CurrentStar ConnectionSummery: Line Voltage vs Phase Voltage1) The line current is equal to the corresponding phase current.2) If the phase voltage is symmetrical, the line voltage is also symmetrical.3) The line voltage is equal to √3 times the phase voltage.4) The phase of the line voltage leads the corresponding phase voltage by 30°. Delta ConnectionSummery: Line Current vs Phase Current1) The line voltage is equal to the corresponding phase voltage.2) If the phase currents are symmetrical, the line currents are also symmetrical.3) The line current is equal to √3 times the phase voltage.4) The phase of the line current lags behind the corresponding phase voltage by 30°.1.4 Three-phase Circuit AdvantagesPower generation: Three-phase power is increased by 50% compared to single-phase power.Transmission: 25% less material than single-phase circuit transmission. That is, under certain conditions, transmitting a certain amount of power by three-phase only requires 75% of the copper of single-phase transmission.Power distribution: More economical than single-phase transformers and easier to connect to the load.Transportation: simple structure, low cost, reliable operation, convenient maintenance.In addition, three wires are usually seen in high-voltage transmission lines, whether on towers or poles, with pin or suspension insulators. Some high-voltage lines are now DC, since solid state devices make it easier to convert to and from AC. The DC lines are free of the problems created by phase, as well as eliminating the skin effect that reduces the effective area of the conductors. It is not nearly as easy to manage long-distance electrical transmission as might be thought.Ⅱ Symmetrical vs Asymmetrical2.1 Symmetrical Three-phase CircuitA symmetrical three-phase power source is usually generated by a three-phase synchronous generator, as shown in Figure (a). Among them, the three-phase windings differ by 120° in space. When the rotor rotates at a uniform angular velocity ω, an induced voltage is generated in the three-phase winding, thereby forming a symmetrical three-phase power supply as shown in Figure (b). Among them, the three ends of A, B, and C are called the start end, and the three ends of X, Y, and Z are called the end. When you connect a load to the three wires, it should be done in such a way that it does not destroy the symmetry.Instantaneous Voltage Calculation of Three-phase PowerIn the formula, take the phase A voltage uA as the reference sine quantity. The three-phase voltage waveform diagram is shown in Figure (a).The key to understanding three-phase is to understand the phasor diagram for the voltages or currents. The phasor of the three-phase power supply can be represented by the Figure (b).The characteristics of the symmetrical three-phase power supply can be derived from the above formula:From the above formula, the sum of the instantaneous value of the three-phase power supply and the sum of the phasor are always zero.The sequence in which each phase of the three-phase power passes through the same value (such as the maximum value) is called the phase sequence of the three-phase power, and the phase sequence of the above-mentioned three-phase voltage is called the positive sequence. Conversely, if phase B exceeds 120° of phase A and phase C exceeds 120° of phase B, this phase sequence is called reverse sequence. If there is no special instructions, it will generally default to positive order.2.2 Three-phase Asymmetry1) In a three-phase circuit, as long as there is asymmetrical part, it is called a three-phase asymmetry.2) The complex power absorbed by the three-phase load is equal to the sum of various complex powers.3) The instantaneous power of a three-phase circuit is the sum of the instantaneous power of each phase load.4) In a three-phase three-wire circuit, whether symmetrical or not, two power meters can be used to measure three-phase power.When the power supply voltage in the three-phase circuit is asymmetrical or the parameters in the circuit are asymmetrical, the current in the circuit is generally asymmetrical. This kind of circuit is called three-phase asymmetry. There are a lot of asymmetry parts in three-phase circuits, and the causes are different. For example, there are many low-power single-phase loads in a three-phase circuit, it is difficult to make them into a completely symmetrical circuit. When a three-phase circuit is broken or short-circuited, it is also a three-phase asymmetry circuit. In addition, some electrical equipment and instruments formally use three-phase asymmetry to work.For example, the most common low-voltage three-phase four-wire system. Due to the large number of single-phase loads in the low-voltage system, the equivalent impedances ZA, ZB, and ZC of the three phases circuit are generally different from each other, and the power supply voltage can generally be considered symmetrical. In this way, a symmetrical three-phase power supply converts to an asymmetrical three-phase load.The circuit shown in the figure has two nodes, and the voltage between the two nodes can be directly calculated according to the node voltage method.Although the power supply voltage in the above formula is symmetrical, the voltage between the neutral point of the power supply and the neutral point of load is not zero due to the load asymmetry, that is, UNN≠0. According to Kirchhoff's voltage law, the phase voltage of the load can be obtained as:The phasor diagram of each voltage corresponding to the above formula is as follows:Ⅲ Power in Three Phase Circuit Formulas1. Average PowerSuppose the power absorbed by a phase load in a symmetrical three-phase circuit is equal to Pp=UpIpcosφ, where Up is the phase voltage and Ip is the phase current of the load. Then the total three-phase power is: P=3UpIpcosφPay Attention To1) φ in the above formula is the phase difference angle (impedance angle) of phase voltage and phase current.2) cosφ is the power factor of each phase, in a symmetrical three-phase system:cosφA=cosφB=cosφC=cosφ3) The formula calculates the circuit power (or the power absorbed by the load).When the load is in a star connection, the line voltage  and line current  at the load end are substituted into the above formula:When the load is in a delta connection, the line voltage  and line current  at the load end are substituted into the above formula:2. Reactive powerThe reactive power absorbed by the load in a symmetrical three-phase circuit is equal to the sum of the reactive power of each phase:3. Apparent Power4. Instantaneous PowerSuppose the voltage and current of phase A of the three-phase load are:Then the instantaneous power of each phase is:It can be proved that their sum isThe above formula shows that the instantaneous power of a symmetrical three-phase circuit is a constant, and is equal to the average power. This is one of the advantages of a symmetrical circuit. For example, on a three-phase motor, a balanced electromagnetic torque is obtained and mechanical vibration is avoided, which is not available in single-phase motors. Ⅳ Frequently Asked Questions about Three-phase Circuit1. What is a 3 phase circuit?Three-phase power is a three-wire ac power circuit with each phase ac signal 120 electrical degrees apart. ... three-phase is that a three-phase power supply better accommodates higher loads. Single-phase power supplies are most commonly used when typical loads are lighting or heating, rather than large electric motors. 2. How many wires are in a 3 phase?four wiresThe three-phase system has four wires. Three are conductors and one is neutral. 3. What is the 3 phase power formula?3-Phase Calculations. For 3-phase systems, we use the following equation: kW = (V × I × PF × 1.732) ÷ 1,000. 4. What is the advantage of three-phase system?A three-phase circuit provides greater power density than a one-phase circuit at the same amperage, keeping wiring size and costs lower. In addition, three-phase power makes it easier to balance loads, minimizing harmonic currents and the need for large neutral wires. 5. What is meant by 3 phase balanced load?A balanced three-phase voltage or current is one in which the size of each phase is the same, and the phase angles of the three phases differ from each other by 120 degrees. ... With such a balanced load, if a balanced three-phase supply is applied, the currents will also be balanced.

IntroductionEarthing (also known as grounding) refers to the process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire, for safety and functional purposes. Generally, the "ground" of electronic equipment has two meanings: one is to connect to the "earth". Taking the earth as the zero potential, connecting the metal shell of electronic equipment and the circuit reference point to the earth can protect the safety of equipment and personnel, such as protective earthing, lightning protection earthing, etc. In addition, the earthing in the weak current system does not necessarily mean the ground connected to the earth in the true sense. It has the effect of improving the stability of the system, shielding and protecting the electromagnetic compatibility of the system, and it can also be connected to the "earth" when necessary.What is Electrical Earthing?CatalogIntroductionⅠ Earthing Basic1.1 Electrical Earthing1.2 Earthing SymbolsⅡ What Are the Types of Earthing?Ⅲ Why Is Electrical Earthing Important?Ⅳ Earthing Q&A You Should KnowⅠ Earthing Basic1.1 Electrical EarthingAn earthing system (UK and IEC) or grounding system (US) connects specific parts of an electric power system with the ground. Earthing is a therapeutic technique that involves doing activities that “ground” or electrically connect you to the earth. In modern earthing concepts, for line engineers, the meaning of this term is usually a reference point of line voltage; for system designers, it is often a cabinet or rack; for electrical engineers, it is safe earthing or connecting to the earth. A more general definition is a low impedance path for current to return to its source. Note that the requirements are "low impedance" and "path".1.2 Earthing SymbolsPE, PGND, FG: Protective ground or chassisBGND or DC-RETURN: Power supply (battery) returnGND: Work groundDGND: Digital groundAGND: Analog groundLGND: Lightning protection groundⅡ What Are the Types of Earthing?There are many types of earthing, including single-point earthing, multi-point earthing and mixed types of earthing. Among them, single-point earthing is divided into series earthing and parallel earthing. Generally speaking, single-point earthing is used for simple circuits, such as earthing distinctions between different functional modules, and low-frequency (f<1MHz) electronic circuits. When designing high frequency (>10MHz) circuits, multi-point earthing or multilayer boards (complete ground plane) should be used. The following are four specific earthing methods.1. Earth FloatingIn electronic design, a commonly used method is floating technology. In this method, the signal ground of the circuit board is not connected to the external public ground, thereby ensuring good isolation of the circuit. The circuit is well isolated from the external ground system and is not easily affected by the interference on the external ground system. However, static electricity is easy to accumulate on the circuit and cause electrostatic interference, which may generate dangerous voltage.Small-scale low-speed (<1mhz) equipment can use earth floating, a single-point connection to the ground by the metal shell.2. Single-point earthing in SeriesThis kind of earthing method is relatively simple, and there is no need to pay so much attention to the circuit board design. So it will be used more. However, this kind of circuit will have common impedance coupling, causing each circuit module to affect each other.3. Single point earthing in ParallelThis method of earthing, although getting rid of the common impedance coupling problem of series single-point earthing, but in actual use, it will introduce too much earthing wire annoying, as to which one needs to be comprehensively evaluated in the actual process. If the circuit board area allows, use the parallel mode, and if the connection between the various circuit modules is kept simple, then use the series mode. In general, there are power modules, analog circuit modules, digital circuit modules and protection circuit modules in the downloaded board. In this case, I use a parallel single-point earthing method.4. Multi-point EarthingMulti-point earthing is used more in daily circuit design, especially in multi-module circuit design. This earthing method can effectively reduce high-frequency interference problems, but it is also prone to cause earthing loops. This point must be fully considered in the design to improve the circuit stability. The working ground of small high-speed (>10MHz) equipment should be grounded at multiple points with its metal casing. The distance between earthing points should be less than 1/20 of the wavelength of the highest operating frequency, and the metal casing should be connected to the ground at a single point.In short, in the design of electronic circuits, the most important point is to reduce the loop area of the circuit, to improve the stability of electronic design and the EMC design of electronic systems. In the actual design, have comprehensive evaluation of the above various earthing technologies to achieve the purpose of improving system stability.Ⅲ Why Is Electrical Earthing Important?As for earthing function, the introduction of earthing technology was originally a protective measure to prevent electrical or electronic equipment from being struck by lightning. The purpose was to introduce the lightning current generated to the ground through the lightning rod, thereby protecting the building. At the same time, earthing is also an effective means to protect personal safety. When the phase line touches the equipment shell caused by some reason (such as poor insulation of wires, aging of wiring, etc.), the equipment shell will have dangerous voltages. The generated fault current will flow through the neutral line to the ground, thereby playing a protective role. With the development of electronic communication and other digital fields, it is no longer sufficient to consider only lightning protection and safety in the earthing system. For example, in a communication system, the interconnection of signals between a large number of devices requires each device to have a reference ground as the signal reference ground. And with the complexity of electronic equipment, the signal frequency is getting higher and higher. Therefore, in the earthing design, special attention must be paid to electromagnetic compatibility issues such as mutual interference between signals. Otherwise, improper earthing will seriously affect the reliability of system operation. Also, the concept of "earthing" has also been introduced in the high-speed signals return technology. Ⅳ Earthing Q&A You Should KnowThe following questions relay on electrical earthing science and grounding physics to explain how electrical charges from the earth can have huge effects on our life. And how do you discharge the electrical energy directly to the earth by earthing technology. Also these Q&A give you considerable attention for the earthing system design and installation.1. What is the difference between earth earthing and electrical earthing?The earth is an object with very low resistance and very large capacitance. It has the ability to absorb infinite charge, and meanwhile can maintain the potential unchanged. Therefore, it is used as the reference potential of a system electrically, that is electrical earthing. In addition, in electronic equipment, when transmitting current and signal conversion at various levels of circuits, a reference potential is required to prevent interference from external signals. This potential is called logical ground or floating ground.2. What is the difference between the ground potential and the logical ground potential?Since the earth can absorb infinite electric charge, the potential of the earth looks macroscopically zero. Due to the influence of the natural electric field and the artificial electric field in the earth, the potential of each point of the earth is different. In engineering, 20m away from the artificial electric field is regarded as zero potential (earthing potential). The electrical ground potential is related to the current injected into the ground by the electrical system. When a large current flows into the electrical ground, the electrical ground potential may reach a very high voltage, especially when the lightning current flows into the electrical ground. The instantaneous potential of the electrical ground can reach 100,000 volts. Therefore, a separate lightning protection earthing point cannot be located in a place where have pedestrians.3. What is the shell?Due to the damage of the insulation layer of the wire, the phase wire is in contact with the outer shell of the electrical equipment, which is called a bumping shell. If the insulation of the phase wires and the enclosure of the electrical equipment does not meet the specified requirements, the equipment cannot be put into use. The reason for the insulation drop may be moisture or damage to the insulation layer, which can be analyzed according to the environment in which the circuit equipment is used.4. What is the step voltage?When an electrical device has a short-circuit fault to the ground, the fault current flows from the fault ground to the ground electrode and returns to the power source. Therefore, an electric field is generated around the ground of the fault point and the ground electrode, which is away from the ground of the fault point or the ground of the ground electrode. The closer, the higher the potential, and the farther, the lower the potential. When the distance between the two feet of a person is about 0.8 meters, standing in this electric field, because the two feet are at different potential points, there will be a potential difference. This potential difference is called the step voltage.5. What is contact voltage?When the insulation of electrical equipment is damaged and a short-circuit occurs to the shell, people who touch the electrical equipment will have the risk of electric shock. To define the degree of danger, the potential of the equipment 0.8 meters away from the horizontal direction of the electrical equipment when it fails is measured. The potential difference between the two is called the contact voltage.6. What is the earthing resistance difference between the earthing electrode and the equipment?The ratio of the earthing voltage to the earthing current is called the earthing resistance of the earthing electrode. When measuring the earthing electrode resistance in a project, an ac voltage is artificially applied to the earthing electrode, and then the current flowing into the earthing electrode is measured. The ratio of the two is the earthing resistance. The earthing resistance of the equipment is the sum of earthing wires resistances.7. What are the classifications of earthing functions?Generally divided into two categories: protective earthing and functional earthing1) Protective earthing can be divided into the following 4 types:Protective earthing: earthing the exposed conductor part of the equipment is called protective earthing. Its purpose is to prevent electrical equipment insulation damage or leakage, which may cause electric shock when people touch it.Lightning earthing: Lead lightning into the earth to prevent electric shock or other property damage.Anti-static earthing: Introduce static charges into the ground to prevent the accumulation of static electricity from causing harm to the human body and equipment.Anti-corrosion earthing: Bury a metal body underground as a sacrificial anode or cathode to protect the metal body connected to it, such as a metal oil pipeline.2) Functional earthing can be divided into the following 4 types:Working earthing: In order to ensure the operation of the power system, earthing is done at an appropriate place in the power system, which is called working earthing. In an AC system, this point is generally a neutral point.Logic earthing: To obtain a stable reference voltage, the appropriate metal parts in the electronic equipment are used as the reference zero potential, and the electronic parts that need to obtain the zero potential are connected to this metal part. This method is called logic earthing.Shield earthing: Ground the metal shell or the metal net to protect the electronic equipment in the shell or the net from external electrical interference, or prevent the electrical equipment in the shell or the net from causing interference to external electronic equipment.Signal earthing: A earthing method set to ensure that the signal has a stable reference potential.8. What is working ground?In order to ensure the safe operation of the electrical device, the earthing of any point (usually the neutral point of the power supply) of the device conductive part is called the working ground.9. What is the relationship between the safety voltage and the use environment?The safety voltage is to prevent personal electric shock. The degree of electric shock is related to the impedance of the human body, and the impedance of the human body has a great relationship with the contact condition. Under different conditions, it is different.The relationship between human body impedance and contact conditions is usually divided into three categories:1) High impedance: dry skin, dry environment, high impedance ground2) Low impedance: moist skin, humid environment, low impedance ground3) Zero impedance: for example, the human body is immersed in water10. What is the difference between short circuit and ground fault?The electrical connection between mutually insulated live conductors due to insulation damage is called a short circuit. For example, between phase wires of different phases, or between a phase wire and a neutral wire, exist an electrical connection, there may be a short circuit. The electrical connection error between the live conductor and the earth is called a ground fault. In addition, live conductors refer not only to the phase line, but also the neutral line. The ground refers to the metal shell of grounded electrical equipment, non-electrical metal pipes and the earth.11. What parts of the earthing device consist of?earthing device is a general term for earthing electrode and earthing wire.The earthing electrode is a conductor buried in the soil or concrete foundation for dissipating current. It can be divided into two types: natural earthing electrode and artificial earthing electrode.There are several types of natural earthing electrodes: the underground metal plumbing systems, the metal structure of the building and the reinforced concrete structure.The artificial earthing electrode should adopt horizontally laid round steel, flat steel, metal earthing plate, and vertically laid angle steel, steel pipe, round steel, etc.12. What are the measures to prevent direct electric shock?Insulate charged objectsUse shields or barriers to block the human body from charged objectsUse leakage switch as additional protection13. What are the measures to prevent indirect electric shock?Set up automatic power-off deviceEquipment with double insulationTake ungrounded local potential connectionElectrical isolation14. What are the types of earthing systems for high-voltage systems?1) Direct earthing, that is, the neutral point of the transformer or generator is connected to the earthing device directly or through a small resistance (such as a current transformer). This kind of earthing method has a large earthing current when a single-phase earthing short circuit occurs, so it is also called the large current earthing system.2) Ungrounded, the neutral point of the transformer in this system is not grounded or connected to earthing equipment such as arc suppression coils, large resistances, and the earthing device.15. Can the natural earthing electrode be used for the earthing of DC electrical devices?The earthing of AC electrical installations should make full use of the natural earthing electrode buried in the ground. For the earthing of DC electrical installations, it is not allowed to use the natural earthing electrode as the PE wire, earthing wire and earthing electrode of the current pattern. The earthing device is connected to the natural earthing. The distance between earthing devices and AC electrical devices shall not be less than 1m to avoid electrical corrosion.16. What is the function of total equipotential bonding?The function of total equipotential bonding (MEB) is to reduce the contact voltage of indirect contact electric shock in the building and different metal parts with different potential, which eliminate the dangerous fault voltage introduced from outside the building through electrical lines and various metal pipes.17. What is supplementary bonding?The two conductive parts are directly connected with wires to make the contact voltage of the fault drop below the contact voltage limit, which is called supplementary or additional equipotential bonding (earthing). When the earthing device fails, the indirect contact protection conditions for automatically cutting off the power supply cannot be met, supplementary bonding should be set. It should also be installed in places with special requirements such as bathrooms, hospitals, and swimming pools.18. What is local equipotential bonding?Local equipotential bonding (LEB) refers to the connection of multiple supplementary equipotential bonding through the bonding terminals in a local board, which is called local equipotential bonding.19. How to check the conductivity of equipotential bonding?1) Welding quality inspection2) Bolt connection quality inspection3) Measure resistance between branch and trunk20. What are the characteristics of arc short circuits?There are two forms of short circuit and ground fault: metallic and arc short. The current of metallic short circuit is very large, which can make the overcurrent protector (circuit breaker or fuse) act in time and the fault is not easy to go on. The short circuit point of arc short circuit has arc or electric spark and the impedance is large, therefore, the short circuit current is small. So overcurrent protection will not take effect. However, the temperature of the arc short-circuit point is very high, which can reach thousands of degrees Celsius locally. It is very easy to ignite the substances around the short-circuit point and cause a fire.Arcing short circuit not only occur in electrical and earthing faults, but poor connections between wires can also cause it. For example, cause flickering of incandescent lamps or interference for TV sets. At this time, you must check whether the connection point of the line is reliable. Frequently Asked Questions about Electrical Earthing System Basics1. What is elecrical earthing and types of earthing?Earthing is the first step towards electrical safety. ... Earthing is done to provide safety to user from electric shock. It is a set of conductors connected in series or in parallel in order to dissipate the potential difference immediately into the ground. The wire connected from equipment to earth called earthing wire. 2. What is difference between earthing and grounding?The key difference between earthing and grounding is that the term “Earthing” means that the circuit is physically connected to the ground which is Zero Volt Potential to the Ground (Earth). Whereas in “Grounding” the circuit is not physically connected to ground, but its potential is zero with respect to other points.Difference between Earthing and Grounding 3. Is grounding the same as earthing?The key difference between earthing and grounding is that the term “Earthing” means that the circuit is physically connected to the ground which is Zero Volt Potential to the Ground (Earth). Whereas in “Grounding” the circuit is not physically connected to ground, but its potential is zero with respect to other points. 4. What is the purpose of earthing?Earthing is used to protect you from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth. It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault. 5. Which wire is used for earthing?copper wiresEarthing Lead or Earthing JointEventhough copper wires are generally used as earthing lead, copper strips are preferred for high installation as it can carry higher values of fault current due to its wider area.