application Related Articles

Ⅰ IntroductionA differential transformer is an electromagnetic inductive displacement sensor that converts mechanical displacement into an electrical signal. It mainly relies on the displacement of the movable iron core in the cylindrical coil and establishes a mutual induction relationship between the input coil and the output coil of the cylindrical coil, and the displacement of the movable core can be obtained by measuring the induced voltage of the output coil proportional to it.  CatalogⅠ IntroductionⅡ The Working Principle and Structure of the Differential TransformerⅢ The Type of Differential TransformerⅣ Linearity and SensitivityⅤ The Cause of the ErrorⅥ The Measurement Circuit  6.1 Differential DC output circuit  6.2 DC differential transformer circuitⅦ The Application of Differential TransformerⅧ Application Circuit Examples of Differential Transformer  8.1 MZK-4R Grinding Machine Automatic Control Device  8.2 ZD41B Short Cylindrical Roller Sorting Machine  8.3 Discussion of Differential Transformer ApplicationⅨ FAQ Characteristics of Differential Transformer(1) There are many types of linear ranges, and it is easy to select according to the use. Usually, there are about 10 types between ±2 mm and ±200 mm.(2) The structure is simple, so the vibration resistance and impact resistance are strong.(3) It does not wear, does not deteriorate, and has excellent durability.(4) The output voltage has a precise ratio to the displacement of the core, that is, the linearity is good. Generally, the full stroke deviation of this sensor is less than 1%, and it can be guaranteed to be ±0.2% to ±0.3% in high-grade products.(5) Because of the high sensitivity, a large output voltage can be obtained, and a small displacement can be detected without requiring an advanced circuit.(6) Since the output changes smoothly, high-resolution detection is possible.(7) The zero point is stable, and its use as a reference point for measurement is good for maintaining accuracy.(8) A high response speed from 500 Hz to 100 Hz can be obtained. Ⅱ The Working Principle and Structure of the Differential TransformerThe structure of the differential transformer is divided into two types: variable-gap type and solenoid type. Since the variable-gap type differential transformer has a small stroke and a complicated structure, it is rarely used at present, and the solenoid type is usually adopted. The basic components of the solenoid type differential transformer include an armature, a primary coil, a secondary coil, and a coil frame. The primary coil acts as excitation and corresponds to the primary side of the transformer. The secondary coil is formed by inverting two coils of the same structural size and parameters to form the secondary side of the transformer. There are two-section, three-section and multi-section according to the initial and secondary arrangement. The zero potential of the three-section is small, the two-section is more sensitive than the three-section, and the linear range is large. The four-section and five-section are all efforts to improve the linearity of the sensor. The working principle of the differential transformer can be explained by the principle of the transformer. The difference is: the general transformer is the closed magnetic circuit, and the differential transformer is the open magnetic circuit; the mutual inductance of the original transformer and the secondary side is constant, and the mutual inductance between the primary and secondary sides of the differential transformer changes as the armature moves. The operation of the differential transformer is based on the change of mutual inductance. The construction principle of the differential transformer is as shown in figure 1, and is composed of a cylindrical coil and a core that is completely separated from it. A typical differential transformer has three cylindrical coils, each of which is one-third of the total length, with a primary coil in the middle and a secondary coil on each side. The iron core added to the cylindrical coil is used to link the magnetic lines of force in the coil to form a magnetic circuit. Figure 1. The Construction Principle of the Differential Transformer When an alternating voltage is applied to the primary coil in the middle (ie, excitation), an electromotive force is generated due to the mutual inductance with the coils at both ends (this is the same as that of a normal transformer). Since the secondary coils are connected in series with each other in opposite polarity, the induced electromotive forces in the two secondary coils are opposite in phase, and as a result of the addition, a potential difference between the two is generated at the output end. At the center of the coil length direction, the induced voltages of the two secondary coils are equal in opposite directions, and thus the output is zero. This position is called the mechanical zero point of the differential transformer (or simply zero points). When the iron core changes position from zero points to a certain direction, the voltage of the secondary coil in the displacement direction increases, and the voltage of the other secondary coil decreases. The product design guarantees that the potential difference is proportional to the displacement of the core. When the iron core moves from zero points to the opposite direction, a proportional voltage is generated, but the phase is 180° different from the previous one. The relationship between the secondary coil voltage and the output voltage difference with respect to the core displacement is shown in figure 2. The range in which the voltage difference is proportional to the core displacement is called the linear range, and its proportionality is called linearity, which is the most important indicator of the differential transformer. Figure 2. The Core Displacement — Output Relationship of Differential Transformer Ⅲ The Type of Differential TransformerThe standard differential transformer consists of a cylindrical coil and a rod-shaped iron core. In actual use, there is also a structure with a guide and a spring. The basis for the classification of differential transformers is as follows: • According to the voltage input to the primary coil(excitation type)Commercial power supply type is suitable for practical measuring instruments of 50-60Hz, 6.3V power supply excitation;Oscillation power supply type is an excitation circuit of 1~5KHz, it is suitable for application measuring instruments requiring certain accuracy and response characteristics;DC power supply type, the semiconductor device is installed in the coil part of the differential transformer to form the excitation oscillation circuit and the secondary output detection circuit inside the coil. It is a differential transformer whose input and output are both DC, called DC-DT. • According to the displacement range of the iron core (displacement type)Small displacement type considers how to measure the small displacement below 0.5mm from the structure;General displacement type is designed for measuring the displacement about 100mm or less;The long-stroke type is designed for long stroke measurement of 120 to 400 mm.  • According to the use environment (environment type)Standard type is used in a normal environment with a temperature of -30℃ to +90℃ and a humidity of about 80%;Environmentally friendly type is the sensor for high temperature, high humidity, waterproof and radioactive environments. Features and SpecificationsWhen using a differential transformer as a position sensor, the selected specifications are as follows:◆ Excitation power supply (frequency, voltage, waveform, etc.);◆ Structure (whether guides and springs are required);◆ Linear range (it is usually ±1%, and that of high-grade products is ±0.5%～±0.2%);◆ Sensitivity (corresponding to the output of the core displacement of 1mm);◆ Impedance (input, output impedance);◆ Connection conditions (cables, sockets, input circuits, etc.);◆ Assembly method (connection method with the object to be tested, etc.);◆Environmental conditions (temperature, humidity, dust, water resistance, rust-proof conditions, etc.). Ⅳ Linearity and Sensitivity• Linearity. The linear range of the differential transformer is affected by the non-uniform magnetic field of the solenoid coil. A reasonable design guarantees the required linear range and linearity.• Sensitivity. The sensitivity of the differential transformer refers to the change of the output potential generated by the armature unit displacement. It can be expressed by mV/mm. In practice, considering the influence of the excitation voltage, it is also commonly expressed by mV/mm/V, that is, the potential change generated by the armature unit displacement divided by the excitation voltage value. The sensitivity of the differential transformer is related to the primary voltage, the number of secondary winding turns, and the frequency of the excitation voltage:• Relationship with secondary turnsThe number of secondary turns increases and the sensitivity increases, which is linear. However, the number of secondary turns cannot be increased indefinitely because the residual voltage at the zero points of the differential transformer also increases.• Primary voltageThe sensitivity is proportional to the primary voltage, but the primary voltage should not be too large. When the voltage is too large, the differential transformer coil will heat up and cause the output signal to drift. Generally, 3~8V is used.• Excitation power frequencyWhen the frequency is very low, the sensitivity increases with increasing frequency; when the frequency increases, the inductance of the coil is much higher than its resistance, the sensitivity is independent of the frequency; when the frequency exceeds a certain value (the value varies depending on the armature material), the effective resistance of the wire increases due to the skin effect of the wire at a high frequency, and the eddy current loss and hysteresis loss of the armature increase, and the output decreases. Figure 3 is the relationship between the input frequency and sensitivity of a certain magnetically permeable material, which can be used as a reference for selecting the excitation frequency. Figure 3. Relationship Between Excitation Frequency and Sensitivity of Differential Transformer Ⅴ The Cause of the ErrorThe error refers to the deviation between the actual and ideal characteristics of the sensor. Here, the system error inherent in the sensor itself and random error is mainly analyzed, and the error in the measurement method is not involved.• Influence of amplitude and frequency of excitation power supplyFluctuations in the magnitude of the excitation supply voltage cause changes in the strength of the excitation field of the coil to directly affect the output potential. The frequency fluctuations have little effect.• The effect of temperature changesChanges in ambient temperature cause changes in the magnetic permeability of the coil and the magnet, causing a change in the magnetic field of the coil to cause temperature drift. This effect is more severe when the coil quality factor is low. The use of constant current source excitation is more advantageous than the constant voltage source. Properly increasing the quality factor of the coil and using a differential bridge can reduce the effects of temperature.• Zero residual voltageWhen the armature of the differential transformer is in the neutral position, the ideal output voltage should be zero. But in fact, when using a bridge circuit, there is always a small voltage value (from a few millivolts to tens of millivolts) at zero point, which is called the zero residual voltage. Figure 4 is an enlarged output characteristic of the zero residual voltage. The dotted line is the ideal characteristic and the solid line indicates the actual characteristics. The presence of a zero residual voltage causes an insensitive zone near the zero point. Figure 4. Zero Residual Voltage of the Differential TransformerThe waveform of the zero residual voltage is very complicated and irregular. It is analyzed to include the fundamental wave in-phase component, the fundamental wave orthogonal component, and the second and third harmonics as well as the electromagnetic interference waves with small amplitude. The reasons why the zero residual voltage is generated are as follows:• Fundamental wave component: Since the winding of the two secondary windings of the differential transformer can not be completely identical in process, its equivalent circuit parameters (mutual inductance, self-inductance and loss resistance, etc.) cannot be completely equal, thus two induced potential values are not equal. The copper loss resistance of the primary coil, the iron loss and material non-uniformity of the magnetically permeable material and the presence of the inter-turn coil capacitance cause the excitation current to be out of phase with the generated magnetic flux.The above factors cause the induced potentials in the two secondary coils to be not only unequal in value but also in phase. The zero residual voltage generated by the difference in phase cannot be eliminated by adjusting the armature displacement. • High-order harmonics: The high-order harmonics are mainly caused by the nonlinearity of the magnetization curve of the magnetically permeable material. Due to the effects of hysteresis loss and magnetic saturation, the excitation current is inconsistent with the magnetic flux waveform, resulting in a non-sinusoidal wave (mainly the third harmonic flux), thereby inducing a non-sinusoidal potential in the secondary winding. The general method for eliminating zero residual voltage:— From the design and process, try to ensure the symmetry of the coil and the magnetic circuit. The structure can adopt the magnetic circuit adjustment mechanism; when selecting the working point of the magnetic circuit, it should be ensured that the magnetic field does not work in the saturation region of the magnetization curve.— Use the appropriate measurement line. The phase-sensitive detection circuit can not only identify the moving direction of the armature but also eliminate the high-order harmonic zero residual voltage of the armature in the middle position. As shown in figure 5, after using the phase-sensitive detection, the characteristic curve of the armature reverse stroke changes from 1 to 2, thereby eliminating the zero residual voltage. Figure 5. Output Characteristics After Phase-sensitive Detection— Use compensation lines. In applications of a differential transformer, there are many circuit types used to eliminate the zero residual voltage, which can be summarized as follows:▲Add series resistors to eliminate the in-phase component of the fundamental wave; generally the resistance of the series resistor is very small such as 0.5~5Ω, and is wound with constant wire.▲Add parallel resistors to eliminate the fundamental wave orthogonal component, but it has an effect on the in-phase component of the fundamental wave; the resistance of the shunt resistor is from tens to hundreds of kiloohms.▲Shunt capacitor, change phase shift, and compensate for high-order harmonics; parallel capacitor value is in the range of 100 ~ 500pf.▲Add feedback winding and feedback capacitor to compensate for fundamental wave and high-order harmonics.In fact, these values are determined experimentally; based on the working principle of the differential transformer and the cause of the zero residual voltage, the above methods can be modified and combined, and it is also possible to design a new compensation circuit. Figure 6 shows some line schematics for compensating for zero residual voltage for reference. Figure 6. Zero Residual Voltage Compensation Circuit of Differential Transformer Ⅵ The Measurement Circuit6.1 Differential DC output circuitThe output voltage of the differential transformer is an AC signal whose amplitude is proportional to the armature displacement. If the output value is measured with an AC voltmeter, it can only reflect the magnitude of the armature displacement and cannot reflect the direction of the displacement. Secondly, there is a certain zero residual voltage in the AC voltage output. Even with various compensation methods, it can only be reduced and cannot be completely eliminated. Therefore, the DC output circuit is commonly used in engineering practice, which can reflect the displacement direction of the armature and compensate for the zero residual voltage. The DC output circuit has two forms: one is a differential phase-sensitive detector circuit, and the other is a differential rectifier circuit.The differential rectifier circuit is shown in Figure 7. This circuit is relatively simple. It does not need to compare the voltage windings. It does not need to consider the influences if the phase adjustment and the zero residual voltage. The influence on the sensing and distributed capacitance can also be ignored. In addition, since the rectifying portion is on the differential output side, the two DC conveying lines are convenient to connect, and can be transported at a long distance, and are widely used. Figure 7. Differential Rectifier Circuita) full-wave current output         b) half-wave current outputc) full-wave voltage output         d) half-wave voltage outputDifferential phase sensitive detector circuits come in many forms. Figure 8 shows two examples, one is a full wave circuit and the other is a half-wave circuit. The phase sensitive detector circuit requires that the comparison voltage and the secondary transformer output voltage of the differential transformer have the same frequency and the same phase or opposite phase.  To ensure this, a phase-shifting circuit is usually connected to the circuit. In addition, it is required that the comparison voltage amplitude should be as large as possible (because the comparison voltage acts as a switch in the detector circuit, and if it is less than the signal voltage, the switch cannot be turned on), generally it should be 3 to 5 times the signal voltage. In the figure, Rw is the bridge zero potentiometer. For the case of measuring small displacements, since the output signal is small, the input amplifier is also connected to the circuit. Figure 8. Differential Phase-sensitive Detection Circuita) full-wave detection         b) half-wave detection6.2 DC differential transformer circuitThe working principle of the DC differential transformer is exactly the same as that of the ordinary differential transformer described above. The only difference is that the power supply used in the instrument is a DC power supply (dry battery, battery, etc.). The schematic diagram of the DC differential transformer is shown in figure 9. It consists of a DC power supply, a multivibrator, a differential rectifier circuit, a filter and so on. Figure 9. Schematic Diagram of DC Differential Transformer CircuitThe multivibrator provides a high frequency excitation power supply for the differential transformer, which can be a square wave, a triangular wave or a sine wave. DC differential transformers are commonly used in the following applications:◆ The measuring point is far from the control room (more than 100m);◆ Simultaneous use of multiple differential transformers and requires no interference with each other and with other equipment;◆ Where explosion protection is required;◆ Requires easy to carry, such as working in the field. Ⅶ The Application of Differential TransformerDisplacement measurement is the most important use of differential transformers. Any physical quantity that can be transformed into a displacement can be measured with a differential transformer. It is noted that the differential transformer measurement is generally contact type. In some cases, it will affect the state of the measured object (such as vibration), which is the so-called “load effect”. In this case, other types of sensors must be used such as eddy current sensors, etc.◆ It can be used as the main component of many precision measuring instruments, such as making high-precision inductance comparator with corresponding measuring devices, which can perform various precise measurements on parts: length, inner diameter, outer diameter, non-parallelism, non-flatness, non-perpendicularity, vibration, eccentricity, and ellipticity.◆ As the main measuring part of the bearing rolling element automatic sorting machine, it can sort large and small steel balls, large and small cylinders, large and small round vertebrae, needle roller and so on.◆ It is used to measure the expansion, elongation, strain, movement, etc. of various parts. With a variety of sensors, its displacement measurement range can be from ±3μm to over 1000mm.◆ Vibration and acceleration measurements. An accelerometer for measuring vibration can be constructed by using a differential transformer and a cantilever beam elastic support.◆ Pressure measurement. The differential transformer and the elastic sensitive component (diaphragm, bellows, spring tube, etc.) can be combined to form a pressure sensor of the open-loop system and a force-balanced pressure gauge of the closed-loop system. Due to the excellent characteristic of differential transformer as the displacement sensor, it has been applied in almost all industrial fields and several specific examples are described below.• Steel industry: blast furnace top-level detection, continuous casting roll gap, sand type vibration, convexity detection, position detection of sliding water nozzles such as ladle and tundish.• Heavy motor industry: the main valve of the steam turbine, the valve lift detection of the bypass valve, and the posture monitoring of the elevator.• Construction machinery industry: Measuring head for numerical control machine tool simulation test.• Ceramic industry: thermal expansion testing of refractory materials, shape detection of templating glass.• Ship and vehicle industry: fuel classification position detection of diesel engine, dynamic characteristic detection of fuel injection valve of an automobile engine, and eccentricity detection of tire and wheel.• Weighing machine industry: a device that automatically measures the weight of the bag, and a weighting machine for the asphalt carrying device.• Measuring instrument, testing machine industry: used for traction test, creep test of metal materials and plastics, signal conversion part of flow meter and liquid level meter, a mechanical test of civil building components.• General industry: spacer separators for assembling bearings, motion deviation detection during stamping, and measurement of workpiece size and shape deviation. Ⅷ Application Circuit Examples of Differential Transformer8.1 MZK-4R Grinding Machine Automatic Control DeviceThis device is used on automatic or semi-automatic grinding machines. During the grinding process of the workpiece, the control device can accurately output 4 signals according to the amount of the pre-regulation to control the introduction of the grinding head, rough grinding, fine grinding, light grinding and exit, etc., thus realizing the automatic measurement and control of the grinding process. • Working process of the grinding machineWhen the workpiece is loaded, the measuring device first enters the workpiece for measurement. If the workpiece size meets the pre-adjusted result, the control device sends a “starting” signal, the grinding head enters the workpiece and moves forward quickly to the machining direction, and coarse grinding starts. Taking the internal grinding as an example, as the workpiece size of the grinding wheel becomes smaller, the output signal of the measuring head also becomes smaller.  When the preset position is reached, the trigger sequentially sends three signals, that is, the “rough grinding end” signal, indicating that the rough grinding is finished, so that the moving speed of the grinding wheel is reduced, and the fine grinding starts; when the fine grinding is finished, the “finishing end” signal is issued, so that the grinding wheel stops moving and the light grinding starts; when the preset size is reached, the “light grinding end” signal is issued to make the grinding wheel and the detection device exit quickly. • Working principle of measuring head (sensor)The measuring head adopts a differential transformer type displacement sensor, and its structure is as shown in figure 10(a). The iron core moves to the right, so that the induced potential of the winding A decreases, and the induced potential of the winding B increases (and vice versa). The two windings and the resistors R1 and R2 in the measuring device form a bridge to realize differential output, as shown in figure 10(b). Figure 10. Schematic Diagram of the Differential TransformerThe primary coil is excited by a square wave generator with a square wave frequency of 3 kHz and an effective voltage value of 3.5V. Along with the change of the displacement of the core, a corresponding voltage variable is generated between the boom of the potentiometer Rw and the secondary common tap (ground) of the measuring head. The displacement-voltage characteristic curve in figure 11 is obtained after the voltage variable is amplified and phase-sensitive rectified. Figure 11. Output Characteristic Curve of Differential TransformerIn the figure, the S-T segment is the full linear range, wherein the H-E segment (high precision) is the ×1 gear indication range, and the K-C segment (low precision) is the ×10 gear indication range. The“start”signal 0 is sent in the D-A segment, the“rough grinding end” signal 1 is sent in the G-B segment, and the“fine grinding end” signal is 2 sent in the 0-F segment. The“light grinding end”signal 3 is sent at point 0. • Principle of the circuit①The circuit block diagram shown in figure 12. Figure 12. Circuit Block Diagram of Control Device②Explanation of the circuit principleThe device consists of six parts: ▲Input bridge, the two arms are composed of two secondary windings of the measuring head, the other two arms are composed of R84 and R85, the potentiometer VR1 is used for the electrical zero points coarse adjustment, the VR2 is used for the zero points fine adjustment, and the R86 is used to limit the zero point adjustment range.In order to obtain the reference voltage for amplifier calibration, a voltage is obtained by the square wave generator, and another bridge is formed by transformers TR4, R88, and R89, and VR4 is used to adjust the reference voltage. ▲The amplifier amplifies the weak signal obtained in the input circuit to have sufficient amplitude to complete the measurement and control. T15, T17, and T18 form a voltage amplifier with gains of about 10, 20, and 20 dB, respectively. T16 is a buffer stage. T19 and T20 form a push-pull power amplifier stage, and the voltage gain of the amplifier is about 60 to 70 dB. In order to achieve higher stability and linearity, deeper negative feedback is added to each stage. The negative feedback of first stage is adjustable, and the total gain of the amplifier is adjusted by VR3. ▲Phase-sensitive rectification and indicating circuit are used to complete the rectification and identify the phase of the input signal. The half-wave rectification circuit is composed of D15 and D16, and the blocking voltage is 13V, which is provided by the square wave generator.The rectified DC ramp signal is used as an input to the trigger on the one hand and as a panel indicator on the other. The μ meter is a microampere meter with a full-scale of 150μA, and full-scale indications of 50μ and 500μ are obtained with shunt resistors R90 and R91. D33 is used as a voltage clamp to protect the meter head. ▲Square wave generator, which is used to generate the excitation voltage required by the measuring head and the blocking voltage required for phase-sensitive rectification. The high rectangular coefficient multivibrator circuit is composed of T21 and T22, which is easy to start, high in frequency and amplitude stability, and its oscillation frequency is 3 to 3.5 kHz. ▲Trigger, according to the comparison of the output voltage of the phase-sensitive rectification and the pre-adjustment voltage, four different control signal outputs are sequentially generated. The circuit adopts a trigger with an emitter coupled by a Zener tube, which has a small temperature drift and convenient backlash adjustment. Among them, VR5, VR6, VR7, and VR8 are used as the adjustment potentiometers for the four signals of “0”, “1”, “2”, and “3” on the panel. ▲Power:-24V, used for power relay after rectification and filtering;-15V, generated by the series regulator circuit and is used as the collector voltage of each transistor and the trigger pre-call;+6V, generated by the shunt regulator circuit and is supplied for the bias and pre-call of the trigger. • Main technical indicators✿ Instrument indexing and error:High precision (G) 1μ/division; full scale -10～+50μ; error ≤1.5μLow precision (D) 20μ/division; full scale -100～+500μ; error ≤30μ✿ Adjustable range of control signal :Signal "0", 350～500μ;Signal "1", 30～100μ;Signal "2", 0 ~ 30μ;Signal "3", -10 ~ +10μ✿ Electrical zero adjustable range:Not less than 100μ, and ±5μ fine adjustment✿ Repeat error:No more than 1μ✿ (Grid) voltage adjustment error:No more than 3μ✿ Instability:Time drift is no more than 10μ/4 hours; temperature drift is no more than 10μ/ 10℃ 8.2 ZD41B Short Cylindrical Roller Sorting MachineThis machine is composed of high-precision micrometer (differential transformer), combined with transistor circuit to form measurement and logic control device to complete the task of automatically sorting short cylindrical bearing rollers. • Main technical indicators◆ Measurement range:length is no more than 15mm5 to 15 mm in diameter◆ Accuracy:1μ, 2μ, 3μIf the magnification and radial grouping potentiometer are re-tuned, any grouping in the range of 0.5 to 5μ can be obtained.◆ Number of groups:10 groups.◆ Speed:28/min to 65/min,can be adjusted arbitrarily • Working principleThe measurement and classification of the radial dimensions of the roller are automated. The roller to be tested is manually placed in a disc-shaped hopper, passed through the vibrating roller to the feeding position along the pipe, and then pushed into the measuring portion by the reciprocating push rod for radial measurement. When different sizes of rollers enter the measurement site for measurement, the differential transformer guide core is displaced in the coil, so that the differential transformer outputs an alternating current signal proportional to the change in the size of the roller, and tiny electrical signal is amplified, rectified, and then amplified by the DC amplifier, so that the corresponding trigger drives the relay and the electromagnet to open the storage valve of the sorting group, so that the measured rollers of different diameters are placed in different sorting bins for automated measurement and sorting. Here we mainly introduce the radial dimension measurement part, namely the differential transformer and its secondary circuit. The measuring part of the roller consists of a differential transformer, a 4KHz oscillator, an attenuator, a low-frequency AC amplifier, a phase-sensitive rectification, a DC amplifier, a regulated power supply, etc. ① Micrometer (differential transformer): The differential transformer is used to convert the diameter of the roller into a change in the amount of electricity. The primary coil is excited by a rectangular wave with a frequency of 4 kHz and an amplitude of 2 to 3 volts. Thus, the voltages of u2 and u3 are induced in the secondary coil. The different names of the secondary coils are connected as a common point ground, and the other ends serve as a differential output and form a bridge balance loop with the resistors R1, R2 and the potentiometer VR.  When the iron core is at the center position of the two secondary coils, since the magnetic resistance of the two coils is equal, the bridge is in a balanced state, and the differential transformer output E2=0 (u2=u3). In a static state, due to the self-weight of the iron core and the guide rod, the iron core is located at the lowermost end of the secondary coil, thus outputting a negative polarity voltage; when the roller is measured, the guide rod is displaced upward, and the iron core is also displaced upward in the differential coil. The output voltage varies with the displacement. When the displacement exceeds the center position, the differential transformer outputs a positive voltage. ② Oscillator: A high-frequency triode is used as a capacitive voltage divider oscillator with an oscillation frequency of 4KHz. This circuit feature avoids the difficulty of inductive oscillator winding. The intermediate transformer is used to couple the output, and then through the first-stage voltage amplification, the two pairs of Zener diodes are used to limit the clipping to form a rectangular wave with constant amplitude (2~3V), one way is for the primary excitation of the differential transformer and the other is for the phase-sensitive rectification comparison voltage. ③ AC amplifier: three-stage amplification circuit and transformer-coupled output. In order to keep the amplifier gain stable, 20dB negative feedback is introduced between the first and second stage, and the total gain is 75~80dB. ④ Phase-sensitive rectifier circuit: diode half-wave phase-sensitive rectification is used, the comparison voltage amplitude is high, and both diodes are turned on in the positive half cycle. The signal voltage is small, the positive voltage is output in the same phase with the comparison voltage, and the negative voltage is output in the opposite phase with the comparison voltage. ⑤ DC differential amplifier: The DC voltage output from the phase-sensitive rectifier circuit is further amplified and the polarity is converted. When inputting ±50mV, the differential output is 4~12V. 8.3 Discussion of Differential Transformer Application(1) The above example uses the two directions of the differential transformer and is determined for the special purpose of roller sorting. When measuring with a roller of nominal size, the differential transformer core is just adjusted to the center position, the positive tolerance roller produces a positive displacement, and the positive voltage is output; the negative tolerance roller produces a negative displacement and outputs a negative voltage. This makes full use of the linear range of the differential transformer. For different applications, especially for small-range, high-precision measurements, there is no need to distinguish the direction of the displacement. It is also possible to use only the displacement of the differential transformer in one direction, and the corresponding circuit can be simplified. (2) This product was a product of the 1970s, so a transistor discrete component circuit was used. Today's electronic technology and the component levels are no longer the same. AC amplifiers and DC amplifiers can be used with operational amplifiers, and performance is much better than discrete component circuits. The basic principles of the circuit and the various functional parts are still applicable and can be designed accordingly. (3) Nowadays, the application of single-chip microcomputers can completely replace the various logic circuits in the past. In the case of a single-chip microcomputer, the entire circuit design may vary greatly. For example, the oscillation source can be digitized (crystal oscillator frequency division may be directly generated by a single-chip microcomputer), and the measurement result is digitized (via A/D conversion), and a large number of analog comparators, triggers can be replaced by program judgment methods.  Furthermore, with the precise timing and synchronization function of the single-chip microcomputer, A/D conversion can be directly performed on the AC signal sampling, and the phase-sensitive rectifier circuit can be omitted. After the measurement results are digitized, data transmission can be used instead of analog transmission, thus precision will not be lost, interference will not exist and transmission distance will be long. Ⅸ FAQ1. Why does LVDT use high voltage?It is a type of electrical transformer used for measuring linear displacement.The linear variable differential transformer has three solenoidal coils placed end-to-end around a tube. The center coil is the primary, and the two outer coils are the top and bottom secondaries. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube. An AC current drives the primary and causes a voltage to be induced in each secondary proportional to the length of the core linking to the secondary.Cutaway view of an LVDT. Current is driven through the primary coil at A, causing an induction current to be generated through the secondary coils at B. When the core is displaced toward the top, the voltage in the top secondary coil increases as the voltage in the bottom decreases. The resulting output voltage increases from zero. This voltage is in phase with the primary voltage. When the core moves in the other direction, the output voltage also increases from zero, but its phase is opposite to that of the primary. The phase of the output voltage determines the direction of the displacement (up or down) and amplitude indicates the amount of displacement.  2. What are the advantages of using an LVDT?• Very reliable: Long sensor lifespan due to near frictionless operation of most models.• Very high resolution: Because of the near-frictionless movement they provide virtually infinite resolution. Even the smallest changes can be detected.• Damage resistant: In some models, both ends of the tube are open, preventing sensor damage if the test article pushes the rod farther than expected (except for collision with the tube itself).• Null point stability: The zero or null point of the sensor is extremely repeatable due to the construction of the sensor itself.• Wide range of operating temperatures: There are LVDT models available that can withstand cryogenic temperatures (-200℃/ -328℉) as well as high temperatures (650℃/ 1200℉)• Low hysteresis/ high positional accuracy and repeatability• Absolute reading output device: As opposed to an incremental output device, the reading from an LVDT will be the same before and after its power is cycled (assuming that the object under test did not move).  3.What are the disadvantages of using an LVDT?• Limited measurement distance: Even the largest LVDTs are limited to less than 1m (~27'') measurement ranges.• Can be affected by magnetic fields (models with shielding are common as a result).• AC models require a precise AC excitation from an LVDT signal conditioner.• DC LVDT models have an inferior shock, vibration and temperature specifications compared to AC LVDT models. 4. How do I interface an LVDT output with PLC?The output is voltage so you will need an analog input card which can take in a voltage input and then inside the PLC you will scale what that voltage corresponds to. For eg 10 V could mean 10 mm or 10 degrees etc. If the output is current them you would need an analog IP card which accepts current. Most common current used is 4–20 mA. 5. What are the applications of the Bourdon tube and the LVDT method for pressure measurement?A bourdon tube is a curved, hollow, closed end tube which can be pressurized. The pressure will attempt to straighten out the tube as it is increased. The amount of movement is typically very small but can be mechanically amplified. The translation of the end of the tube can be a linear indication of the pressure applied to the other end.Pressure gauges have used this technique for over a century and a half to indicate pressure manually on a dial gauge with a linkage that moves a dial pointer.To make electronic readouts of pressure to remote dials or to computers, a linear movement to electrical voltage is needed. An LVDT satisfies this need. An LVDT is a variable transformer consisting of a movable magnetic core sliding inside a tube with a primary and secondary winding. As the core is displaced the coupling between windings is varied linearly. If a small AC voltage is applied to the primary then the amplitude of the secondary output can be measuered in amplitude to indicate proportional to the pressure.So this makes a hybrid sensor or transducer, pressure to displacement connected to a displacement to variable voltage resulting in a pressure to variable voltage device.Technically this is an older way of converting pressure to volts… and is subject to hysteresis or mechanical backlash. Most modern P-V transducers use strain gauge bridge followed by an instrumentation amplifier to have fewer moving parts and less hysteresis. 6. Discuss various applications where LVDT’s can be used?They can be used in any application where a highly accurate measurement of linear displacement or position is needed. This includes precision gaging systems for measurement and metrology, feedback transducers for precision servomechanisms, torque, force and moment transducers, materials testing equipment (tensile testers, rheometers, fatigue testers, etc.). 7.What is the accuracy of a LVDT and an inductance transducer in a displacement measurement?Accuracy for both devices depends on the way they are designed, made and used, and the materials from which they are made. As well as calibration.However, neither on their own give “readings”. They need conditioning and interface circuitry. (I do recognise that the “inductance transducer” is a two-word item, and that the second word - transducer - implys that at least some form of signal conditioning exists therein.)That cicuitry is at least as important as the device itself.To give typical values for accuracy, is difficult without more specifics, though it is usual to be able to achieve several significant figures of accuracy out of each. 8. What is LVDT in measurement?A Linear Variable Differential Transducer is a sensor based on the idea of transformers. As its name shows it's a Linear sensor used in measuring displacements.  It has an iron core that moves up and down in the gap separating the primary and secondary coils. So the coils are not physically connected. The secondary coils are connected in opposition such that the output voltage is the difference between the voltages induced in the first and second secondary coils. The components whose Displacement is required to be measured should be connected to the core, so the input to the sensor is the displacement، the output would be the differential voltage output and after some manipulation using the sensitivity and sensor resolution, the displacement can be obtained. 9. How does a DC LVDT work?An oscillator/demodulator circuit built into the displacement transducer supplies the excitation and converts the return signal to a dc voltage. ... As the transducer contains internal signal conditioning electronics, there is no need for external signal conditioning. 10. Is LVDT an active transducer?The active transducer is also called a self-generating type transducer. ... Example of an active transducer is the bourdon tube. An example of a passive transducer is LVDT (linear variable differential transformer). It generates electric current or voltage directly in response to environmental stimulation.

CatalogⅠ IntroductionⅡ What is an infrared sensor?Ⅲ How does the infrared sensor work?Ⅳ The basic law of infrared radiationⅤ The working principle of the infrared sensorⅥ Types of infrared sensors  6.1 Thermal sensor  6.2 Photon sensorⅦ Application and Prospect of the infrared sensorⅧ SummaryⅨ FAQⅠ IntroductionAny object in the universe can produce infrared radiation as long as its temperature exceeds zero. In fact, like visible light, its radiation can be refracted and reflected, which leads to infrared technology. Infrared detector is widely used in military and civil fields because of its unique advantages. In the military, infrared detection is used for guidance, fire control tracking, alert, target detection, weapon thermal sight, ship navigation, etc.; in the civil field, it is widely used in industrial equipment monitoring, safety monitoring, disaster relief, remote sensing, traffic management, medical diagnosis technology, etc.With the development of science and technology, the proportion of automatic control and automatic detection in people's daily life and industrial control is more and more heavy, which makes people's life more and more comfortable and the efficiency of industrial production higher and higher. The sensor is an important component of the automatic control, and an important component of the information acquisition system.  Through the sensor, the feeling or response is measured and converted into a signal suitable for transmission or detection (generally electrical signal), and then the computer or circuit equipment is used to process the signal from the sensor to achieve the function of automatic control. Because the response time of the sensor is generally short, the real-time control of industrial production can be carried out through the computer system. The infrared sensor is a common type of sensor.  Because an infrared sensor is a kind of sensor to detect infrared radiation, and any object in nature will radiate infrared energy as long as its stability is higher than absolute zero, so infrared sensor is called a very practical type of sensor. Many practical sensor modules can be designed by using infrared sensors, such as infrared temperature measurement Instruments, infrared imagers, infrared human detection alarms, automatic door control systems, etc.Ⅱ What is an infrared sensor?Infrared sensor is a sensor that uses the physical properties of infrared to measure. Infrared light, also known as infrared light, has the properties of reflection, refraction, scattering, interference, absorption, etc. It is a kind of invisible light, its spectrum is located outside red in visible light, so it is called infrared. In engineering, the position (band) of infrared rays in the electromagnetic spectrum is divided into four bands: near infrared band, mid infrared band, far infrared  band and extremely far infrared band. Any substance can radiate infrared ray, as long as it has a certain temperature (higher than absolute zero).Ⅲ How does the infrared sensor work?First of all, let's learn about infrared light. Infrared light is a part of the solar spectrum. The biggest characteristic of infrared light is its photothermal effect and radiant heat. It is the largest photothermal effect area in the spectrum. An invisible light, like all electromagnetic waves, having the properties of reflection, refraction, scattering, interference, absorption, etc. The propagation speed of infrared light in a vacuum is 300000 km / s. The transmission of infrared light in the medium will produce attenuation, and the transmission attenuation in the metal is very large, but the infrared radiation can pass through most semiconductors and some plastics, and most liquids absorb the infrared radiation very much.Different gases have different absorption levels, and the atmosphere has different absorption bands for different wavelengths of infrared light. The results show that the infrared light with the wavelength of 1-5 μ m and 8-14 μ m has a relatively large "transparency". That is to say, these wavelengths of infrared light can penetrate the atmosphere well. Any object in nature, as long as its temperature is above absolute zero, can produce infrared radiation. The photothermal effect of infrared light is different for different objects, and the intensity of heat energy is also different.  For example, blackbody (an object that can fully absorb the infrared radiation projected on its surface), mirror body(an object that can fully reflect the infrared radiation), transparent body(an object that can fully penetrate the infrared radiation) and gray body (an object that can partially reflect or absorb the infrared radiation) will produce different photothermal effects. Strictly speaking, there are no blackbody, mirror body and transparent body in nature, and most of the objects belong to gray body. These characteristics are the important theoretical basis for the application of infrared radiation technology in military and scientific research projects such as satellite remote sensing and infrared tracking. The physical essence of infrared radiation is thermal radiation. The higher the temperature of an object, the more infrared it radiates, the stronger the energy of the infrared radiation. It is found that the thermal effect of various monochromatic light in the solar spectrum increases gradually from violet light to red light, and the largest thermal effect occurs in the frequency range of infrared radiation, so people call infrared radiation as thermal radiation or thermal ray.Ⅳ The basic law of infrared radiation① Kirchhoff's Law: at a certain temperature, the ratio of the radiation flux W per unit area of the ground object to the absorption rate is a constant for any object, and is equal to the radiation flux w of a blackbody of the same area at that temperature. At a given temperature, the emissivity of the object = the absorptivity (the same band); the higher the absorptivity, the higher the emissivity. The thermal radiation intensity of the ground object is directly proportional to the fourth power of the temperature, so the small temperature difference of the ground object will cause the obvious change of the infrared radiation energy. This feature constitutes the theoretical basis of infrared remote sensing.② Boltzmann's Law: that is, the total radiation flux of blackbody increases rapidly with the increase of temperature, which is proportional to the fourth power of temperature. Therefore, a small change in temperature will cause a great change in radiation flux density. It is the theoretical basis of measuring temperature with an infrared device. ③ Wien displacement law: with the increase of temperature, the peak wavelength corresponding to the maximum radiation value moves to the short wave direction.Ⅴ The working principle of the infrared sensorThe working principle of the infrared sensor is not complicated. The entities of each part of a typical sensor system are as follows:• Target to be tested: the infrared system can be set according to the infrared radiation characteristics of the target to be tested.• Atmospheric attenuation: when the infrared radiation of the target to be measured passes through the earth's atmosphere, the infrared radiation from the infrared source will be attenuated due to the scattering and absorption of gas molecules, various gases and various colloidal particles.• Optical receiver: it receives part of the infrared radiation of the target and transmits it to the infrared sensor. Equivalent to radar antenna, usually objective lens.• Radiation modulator: it can modulate the changed radiation light from the target to be tested, provide the target orientation information, and filter out large-area interference signals. Also known as modulation disk and chopper, it has a variety of structures.• Infrared detector: This is the core of the infrared system. It is a sensor that uses the physical effect of the interaction between infrared radiation and matter to detect infrared radiation. In most cases, it uses the electrical effect of the interaction. These detectors can be divided into two types: photon detector and heat-sensitive detector.• Detector Cooler: because some detectors must work at low temperatures, the corresponding system must have refrigeration equipment. After refrigeration, the equipment can shorten the response time and improve the detection sensitivity.• Signal processing system: amplify and filter the detected signals, and extract information from these signals. Then, this kind of information is transformed into the required format, and finally transmitted to the control equipment or display.• Display device: This is the terminal device of infrared device. Commonly used displays include oscilloscopes, picture tubes, infrared sensitive materials, indicating instruments and recorders.According to the above process, the infrared system can complete the corresponding physical quantity measurement. The core of infrared system is infrared detector. According to the different detection mechanism, it can be divided into two categories: thermal detector and photon detector. The thermal detector absorbs all the radiant energy of all kinds of incident wavelengths. It is an infrared sensor with no choice for infrared light wave. The common photon effects of photon detectors are external photoelectric effect, internal photoelectric effect (photovoltaic effect, photoconductive effect) and photoelectromagnetic effect. The thermal detector uses the radiation heat effect to make the temperature rise after the detector receives the radiation energy, and then the temperature-dependent performance of the detector changes.  Radiation can be detected by detecting a change in one of the properties. In most cases, radiation is detected by thermoelectric changes. When the element receives radiation and causes the physical change of non electric quantity, the corresponding electric quantity change can be measured after appropriate transformation. The response time of thermal detector to infrared radiation is much longer than that of photodetector. The response time of the former is generally more than MS, while that of the latter is only ns. Thermal detectors do not need to be cooled, most photon detectors need to be cooled.Ⅵ Types of infrared sensorsCommon infrared sensors can be divided into thermal sensors and photon sensors.6.1 Thermal sensorThe thermal sensor uses the incident infrared radiation to change the temperature of the sensor, and then make the relevant physical parameters change accordingly. The infrared radiation absorbed by the infrared sensor is determined by measuring the changes of the relevant physical parameters. The main advantage of the thermal detector is that it has a wide band, can work at room temperature and is easy to use. However, the thermal sensor has a long response time and low sensitivity, which is generally used in low frequency modulation.The main types of thermal sensors are thermal sensor type, thermocouple type, gaolai pneumatic type and heat release electric type. ① Thermistor sensorThe thermistor is made of manganese, nickel and cobalt oxides. The thermistor is usually made into thin sheet. When the infrared radiation irradiates the thermistor, its temperature increases and the resistance decreases. By measuring the change of the thermistor value, we can know the intensity of the incident infrared radiation, thus we can judge the temperature of the object generating the infrared radiation.② Thermocouple sensorThermocouples are made of two materials with a great difference in thermal power. When infrared radiation reaches the contact of the closed circuit composed of these two metal materials, the contact temperature increases. The other contact which is not irradiated by infrared radiation is at a lower temperature, at this time, the temperature difference current will be generated in the closed circuit. At the same time, thermoelectric potential is generated in the loop, and the magnitude of thermoelectric potential reflects the strength of infrared radiation absorbed by the contact. The infrared sensor made of thermoelectric potential is called thermocouple infrared sensor. Because of its large time constant, long corresponding time and poor dynamic characteristics, the modulation frequency should be limited below 10Hz.③ Lai pneumatic sensorAfter absorbing the infrared radiation, the temperature and volume of the gas are increased to reflect the intensity of the infrared radiation. It has an air chamber connected to a flexible sheet by a small pipe.  One side of the back pipe of the sheet is a reflector. The front of the gas chamber is attached with an absorption mode, which is a thin film with low heat capacity. The infrared radiation is incident on the absorption mode through the window, and the absorption mode transmits the absorbed heat energy to the gas, which makes the gas temperature and pressure increase, so that the flexible mirror moves.  On the other side of the chamber, a beam of visible light is focused on the flexible mirror through the grating light bar, and the grating image reflected by the flexible mirror is projected onto the photoelectric cell through the grating light bar. When the flexible mirror moves due to the change of pressure, the relative displacement between the grating image and the grating light bar will change the amount of light falling on the photocell, and the output signal of the photocell will also change, which reflects the intensity of the in-out infrared radiation.  This sensor is characterized by high sensitivity and stable performance. But the response time is long, the structure is complex and the intensity is poor, so it is only suitable for laboratory use. ④ Pyroelectric sensorPyroelectric sensor is a kind of thermal crystal or ferroelectric with polarization phenomenon. The polarization intensity (charge per unit area) of ferroelectrics is related to temperature. When infrared radiation irradiates the surface of the polarized ferroelectric sheet, the temperature of the sheet increases, the polarization intensity decreases, and the surface charge decreases, which is equivalent to releasing part of the charge, so it is called pyroelectric sensor.  If the load resistor is connected to a ferroelectric sheet, an electrical signal output is generated on the load resistor. The size of the output signal depends on the speed of the temperature change of the chip, which reflects the intensity of the incident infrared radiation. It can be seen that the voltage response rate of the pyroelectric infrared sensor is directly proportional to the change rate of incident radiation. When the constant infrared radiation irradiates on the pyroelectric sensor, the sensor has no electrical signal output.  Only when the temperature of ferroelectrics is in the process of change can the electrical signal be output. Therefore, it is necessary to modulate the infrared radiation (or chopping light) so that the constant radiation becomes the alternating radiation, which constantly causes the temperature change of the sensor, so as to generate pyroelectric and output the alternating signal.6.2 Photon sensorThe photon sensor uses some semiconductor materials to produce photon effect under the illumination of incident light, which changes the electrical properties of materials. By measuring the change of electrical properties, we can know the intensity of infrared radiation. The infrared sensors made by photon effect are called photon sensors. The main characteristics of photon sensor are high sensitivity, fast response speed and high response frequency, but generally it must work at low temperature and the detection band is narrow. According to the working principle of photon sensor, it can be divided into internal photoelectric sensor and external photoelectric sensor. The latter is divided into photoconductive sensor, photovoltaic sensor and magnetoelectric sensor. ① External photoelectric sensorWhen the light radiates on the surface of some materials, if the photon energy of the incident light is large enough, the electrons of the materials can escape from the surface. This phenomenon is called external photoelectric effect or photoelectron emission effect. Photodiode, photomultiplier tube and so on belong to this type of electronic sensor. Its response speed is relatively fast, generally only a few nanoseconds. However, electron escape requires a large amount of photon energy, which is only suitable for near-infrared radiation or visible light. ② Photoconductive sensorWhen infrared radiation irradiates on the surface of some semiconductor materials, some electrons and holes in the semiconductor materials can change from the original non-conductive bound state to the conductive free state, which increases the conductivity of the semiconductor. This phenomenon is called the photoconductivity phenomenon. The sensors made of photoconductive phenomena are called photoconductive sensors.  For example, lead sulfide, lead selenide, indium antimonide, mercury telluride and other materials can be used to make photoconductive sensors. When using photoconductive sensor, we need to cool and add a certain bias voltage, otherwise, the response rate will be reduced, the noise will be large, the response band will be narrow, and the infrared sensor will be damaged.③ Photovoltaic sensorWhen the infrared radiation irradiates on the PN junction of some semiconductor materials, the free electrons move to the N-region under the action of the electric field in the junction. If the PN junction is open, an additional potential will be generated at both ends of the PN junction, which is called the photogenerated electromotive force.  The sensors or PN junction sensors based on this effect are usually made of materials such as indium arsenide, indium antimonide, mercury telluride, lead-tin telluride, etc. ④ Magnetoelectric sensorWhen the infrared radiation irradiates on the surface of some semiconductor materials, some electrons and holes in the semiconductor materials will diffuse to the interior. If the diffusion is affected by a strong magnetic field, the electrons and holes will each deviate to one side, resulting in an open circuit voltage. This phenomenon is called the optical magnetoelectric effect. The infrared sensor made of this effect is called magnetoelectric sensor. The response band is about 7 μ m, the time constant is small, the response speed is fast, there is no bias, the internal resistance is very low, the noise is small, and it has good stability and reliability. However, its sensitivity is low and it is difficult to make low noise preamplifier, which affects its use.Ⅶ Application and Prospect of the infrared sensor (1) The application of infrared sensor is mainly reflected in the following aspects:    1. Infrared radiometer: used for radiation and spectral radiation measurement.    2. Search and tracking system: used to search and track the infrared target, determine its spatial position and track its motion.    3. Thermal imaging system: it can form the infrared radiation distribution image of the whole target.    4. Infrared ranging system: to measure the distance between objects. (it uses the non-proliferation principle of infrared propagation, because the refractive index of infrared is very small when it passes through other substances, so infrared will be considered in long-distance distance distance rangefinders.)    5. Communication system: infrared communication as a way of wireless communication.    6. Hybrid system: refers to two or more combinations of the above systems.Infrared sensor applications can be used for non-contact temperature measurement, gas composition analysis, nondestructive testing, thermal image detection, infrared remote sensing and military target reconnaissance, search, tracking and communication. With the development of modern science and technology, the application prospect of infrared sensor will be more broad. In the future, the performance and sensitivity of infrared sensor will be improved greatly.  (2) Development trend    1. Intellectualization: at present, the infrared sensor is mainly used in combination with peripheral equipment. The built-in microprocessor of the intelligent sensor can realize the two-way communication between the sensor and the control unit. It has the advantages of miniaturization, digital communication, simple maintenance, etc., and it can work independently as a module.     2. Miniaturization: an inevitable trend of sensor miniaturization. Now in application, because of the volume problem of infrared sensor, its use degree is far worse than that of thermoelectric corner. Therefore, whether the infrared sensor is miniaturized and portable or not can't be ignored.     3. High sensitivity and high performance: in medicine, the infrared sensor has been widely used for the measurement of human body temperature, but it can not replace the existing temperature measurement method due to its low accuracy. Therefore, the high sensitivity and high performance of infrared sensor is the inevitable trend of its future development.Ⅷ SummaryAlthough there are many deficiencies in the current infrared sensor, the infrared sensor has played a huge role in modern production practice. With the improvement of detection equipment and other parts of the technology, the infrared sensor can have more performance and better sensitivity and will have a broader application range. Ⅸ FAQ1. What is the working principle of the IR sensor?Active infrared sensors both emit and detect infrared radiation. Active IR sensors have two parts: a light-emitting diode (LED) and a receiver. When an object comes close to the sensor, the infrared light from the LED reflects off of the object and is detected by the receiver. 2. Why is an infrared sensor important?An infrared sensor is an electronic instrument that is used to sense certain characteristics of its surroundings. It does this by either emitting or detecting infrared radiation. Infrared sensors are also capable of measuring the heat being emitted by an object and detecting motion. 3. What is an IR sensor for kids?Light waves longer than red light waves are called infrared light (IR). We cannot see either UV and IR light without special equipment or photography. In the case of infrared sensors, an infrared light source, which is typically an IR LED, is used to transmit light to a receiving infrared sensor. 4. Can IR sensors detect humans?The Passive Infrared (PIR) sensor is used to detect the presence of humans. But this detects the human only if they are in motion. Every human radiates the infrared energy of a specific wavelength range. The absorbed incident radiation changes the temperature of a material. 5. Where are IR sensors used?A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. PIR sensors are commonly used in security alarms and automatic lighting applications. 6. How do you bypass an infrared sensor?Most motion detectors, even newer ones, use infrared to detect significant changes in the surrounding room's temperature, Porter said. Normally, walking around in a room would set off these sensors, but using something as simple as a piece of styrofoam to shield your body can trick them, he said. 7. What is the difference between an IR sensor and an ultrasonic sensor?The biggest difference between IR sensors vs. ultrasonic sensors is the way in which the sensor works. Ultrasonic sensors use sound waves (echolocation) to measure how far away you are from an object. On the other hand, IR sensors use Infrared light to determine whether or not an object is present. 8. What is the range of the IR sensor?An infrared sensor (IR sensor) is a radiation-sensitive optoelectronic component with spectral sensitivity in the infrared wavelength range 780 nm ...50 µm. IR sensors are now widely used in motion detectors, which are used in building services to switch on lamps or in alarm systems to detect unwelcome guests. 9. Can an IR sensor detect temperature?Infrared temperature sensors sense electromagnetic waves in the 700 nm to 14,000 nm range. ... Because the emitted infrared energy of any object is proportional to its temperature, the electrical signal provides an accurate reading of the temperature of the object that it is pointed at. 10. How do IR sensors detect obstacles?An infrared sensor emits and/or detects infrared radiation to sense its surroundings. ... The basic concept of an Infrared Sensor which is used as an Obstacle detector is to transmit an infrared signal, this infrared signal bounces from the surface of an object and the signal are received at the infrared receiver. 

Introduction Diodes are widely used in electronics, such as rectification in power supply, as detection and mixing, etc. in communications, and are often used in voltage regulation and protection in various circuits (such as freewheeling diodes, TVS and so on). Due to the wide variety and versatility, the following is an analysis of the simple application of Schottky diodes in digital circuits.In this video, the Schottky diode has been explained.CatalogIntroductionⅠ Schottky Diodes CharacteristicsⅡ Schottky Diode Applications2.1 As Dual Power Supply2.2 As AND Gate2.3 As OR GateⅢ Schottky Diode ParametersⅣ Example AnalysisⅠ Schottky Diodes CharacteristicsThe Schottky diode is structurally different from the PN junction diode. It is made of an anode metal (a barrier layer made of a material such as molybdenum or aluminum), SiO2 (electric field eliminating material), and N- epitaxial layer (arsenic material), the N-type silicon substrate, N+ cathode layer, and the cathode metal, which are as shown in the following figure. A Schottky barrier is formed between the N-type substrate and the anode metal. When a forward bias is applied to both ends of the Schottky barrier (anode metal is connected to the positive electrode of the power supply, and the N-type substrate is connected to the negative electrode), the Schottky barrier layer is narrowed, and the internal resistance becomes small. On the contrary, when a reverse bias is applied across the Schottky barrier, it becomes wider and its internal resistance becomes larger. Figure 1. Schottky Diode Structure Ⅱ Schottky Diode ApplicationsThe problem with Schottky diodes is that the withstand voltage is relatively low and the reverse leakage current is large. At present, the general condition of the Schottky diode used in the power conversion circuit is that the withstand voltage is below 150V, the average current is below 100A, and the reverse recovery time is between 10 and 40ns. Therefore, Schottky diodes are ideal device for use in high frequency and low voltage circuits.2.1 As Dual Power SupplyAt present, in the electronic design with the main controller, the real-time clock (RTC) is basically used, and the RTC needs an additional button battery to support, to avoid information lost after the system is powered off. And meanwhile, after the system is started, in order to extend the battery life, the main system is often supplied with power. Therefore, RTC often requires dual power supply, and the diode can be used for power isolation due to its single-conductivity. Taking the small-signal Schottky diode BAT54C as an example, the forward voltage drop is only 0.24v (the forward current is 0.1mA), and the RTC current consumption is uA-level, after adding the Schottky diode to isolate power supply to save info security.2.2 As AND GateAs shown in the figure below, n Schottky diodes form the AND gate of the n input. As long as there is a signal output logic 0 in A1~An, the Output is logic 0, only all signals in A1~An output logic 1, Output can output logic 1. That is, the phase sum of the signals A1~An is realized. Since the chip signal input stage is basically high-resistance in the digital circuit, the overall current of the AND gate circuit composed of the Schottky diode is uA-level, and the Schottky diode voltage drop is extremely small. In the case of it, the flat can still meet the design requirements.  Figure 2. Schottky Diode as AND Gate2.3 As OR GateAs shown in the figure below, n Schottky diodes form an n-input OR gate. As long as there is a signal output logic 1 in A1~An, Output outputs a logic 1. Only all signals in A1~An output logic 0, and Output can output logic 0. That is, the phase sum of the signals A1~An is realized.  Figutre 3. Schottky Diode as OR Gate Ⅲ Schottky Diode ParametersNote: Because Schottky diodes are used differently in different electronic circuits, we also need to consider the following parameters when using them.1）Forward voltage drop VFVF is the forward voltage drop when the diode is forward conducting. The greater the current through the diode, the larger the VF, in addition, the higher the diode temperature, the smaller the VF.2）Reverse saturation drain current IRIR refers to the current flowing through the diode when a reverse voltage is applied to the diode. The Schottky diode has a large reverse leakage current, therefore, selecting a Schottky diode with a smaller IR.3）Rated current IFIt refers to the average current value calculated from the allowable temperature rise when the diode is in a long time operation.4）Maximum surge current IFSMExcessive forward current that is allowed to flow. It is not a normal current, but an instantaneous current, which is quite large.5）Maximum peak inverse voltage VRMEven if there is no reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later. This reverse voltage is not the instantaneous voltage, but the reversed voltage that is added repeatedly. Since the rectifier is supplied with an alternating voltage, its maximum value is a specified important factor. And the maximum reverse peak voltage VRM refers to the maximum reverse voltage that can be applied to avoid breakdown. At present, Schottky's highest VRM value is 150V.6）Maximum DC reverse voltage VRVR is the value when the DC voltage is continuously applied. For DC circuits, the maximum DC reverse voltage is important to determine the allowable and upper limits.7）Maximum operating frequency FMDue to the junction capacitance of the PN junction, when the operating frequency exceeds a certain value, its unidirectional conductivity will deteriorate. And Schottky diodes have high FM values up to 100 GHz.8）Reverse recovery time TrrWhen the operating voltage changes from a forward voltage to a reverse voltage, the ideal operation of the diode is that the current can be instantaneously turned off. In fact, it usually takes a little delay. The amount that determines the current cut-off delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it does not mean that this value is small. That is, when the diode is suddenly reversed by conduction, the reverse current is greatly attenuated to a time required to approach IR. This indicator is important when the high-power switch is operating in the high-frequency state.9）Maximum dissipation power PWhen a current flows through the diode, it absorbs heat and raises its temperature. In reality, the external heat dissipation condition also has a great influence on P. Specifically, the voltage applied across the diode is multiplied by the current flowing through and the reverse recovery loss. Schottky Diode Symbols Ⅳ Example AnalysisIn digital circuit design, it is often necessary to make simple phase, or phase inversion of some signals. If the logic chip such as the 74 series is directly used, not only the layout area is greatly increased, but also the wiring is not flexible. The use of small-signal Schottky diodes and OR gates is more flexible and easy to use. The following figure shows a simple two-way reset circuit. JTAG generating a reset signal needs to reset the master, and the external reset button also needs to reset the master when pressed. If the JTAG reset and button reset directly to the reset pin of the master, it may cause damage to the JTAG emulator. For example, when the reset button is pressed, the JTAG output reset pin will be directly lowered. The phase and circuit are formed by the Schottky diode BAT54A , and the signal outputs do not affect each other. The following figure allows the master to reset as long as the JTAG output logic 0 or pressing the button reset output logic 0.Figure 4. Schottky Diode BAT54A ApplicationIf it is to be used as a non-gate, a triode can be used. Of course, the triode is widely used in electronics, such as a switching device in a digital circuit, as a current drive, level shifter, and the like. Frequently Asked Questions about Small Signal Schottky Diodes1. What is the Schottky diode and how it works?A typical diode combines p-type and n-type semiconductors to form a p-n junction. In a Schottky diode metal replaces the p-type semiconductor. This metal can range from platinum to tungsten, molybdenum, gold, etc. When metal is combined with an n-type semiconductor an m-s junction is formed. 2. What does small signal mean?A small signal is an AC signal (more technically, a signal having zero average value) superimposed on a bias signal (or superimposed on a DC constant signal). This resolution of a signal into two components allows the technique of superposition to be used to simplify further analysis. 3. Which statement is correct for Schottky diode?Explanation: The majority charge carriers in a Schottky diode are electrons not holes. Explanation: Due to the metal-silicon junction there are no stored charges hence, no reverse recovery time, due to which the switching is faster. 4. What are the two important features of a Schottky diode?We have seen here that the Schottky Diode also known as a Schottky Barrier Diode is a solid-state semiconductor diode in which a metal electrode and an n-type semiconductor form the diodes ms-junction giving it two major advantages over traditional pn-junction diodes, a faster switching speed, and a low forward bias.

DescriptionIt's not weird to discover that applications are becoming more complex,with connectivity just one of the drivers. And,as it become more complex.the number of sensors grows,as does the need for more capable user interfaces. At the same time,algoriths need more processing power,wireless stacks mandate larger memories and power budgets are shrinking.In order to coping with the growing list of demands, a great number of leading MCU manufacturers have recently launched Micro Controller Unit built around the ARM Cortex-M4 core. BodyThe M3 is general purpse and the M0+is low cost but the M4 is a more capable core in general if look at the Cortex range. Oivind Loe,a senior strategic marketing manager with Sillicon Laboratories said. Microchip's product marketing manager--Anand Rangara commented:“Something that sat around without the need to communicate now needs connectivity. When that happens, you need more flash and RAM, as well as graphics capability and perhaps the ability to support a touch interface. All this has to be offered at good power/performance and an attractive price.”  'Industrial Strength' MCUsSilicon Labs has expanded its EFM32 Gecko portfolio with what it calls ‘industrial strength’ MCUs. It says the EFM32GG11 Giant Gecko MCU family offers the ‘most advanced’ feature set available in the low-power MCU market.Loe noted that MCU development isn’t just about power. “It’s also about executing tasks efficiently. A simple program with a few clocks will run efficiently on an M0+ core. But if the workload is larger, the M4 core has some special instructions that can allow it to use less energy than the M0+ and more efficiently than some larger cores – and that's crucial for a range of application.” GG11 Geckos offer up to 2Mbyte of flash and 512kbyte of RAM to accommodate more code and comms stacks, such as a 10/100 Ethernet MAC and a dual CAN interface. Looking to meet power budgets, the parts boast an active power consumption of 77μA/MHz, while drawing 1.6μA in deep sleep mode. FPU to Increase System EffiencyMicrochip’s SAM D5x/E5x MCUs also take advantage of the Cortex-M4’s floating point unit (FPU) to increase system efficiency. Running at up to 120MHz, the D5x and E5x MCUs come with up to 1Mbyte of dual-panel flash and up to 256kbyte of SRAM. Rangarajan noted: “We’ve listened to our customers, so we’ve included more connectivity in these MCUs. But it's not just about adding memory , it’s also about more performance and the ability to provide more flexible peripherals, interfaces and connectivity options.” Meanwhile,he  pointed out that the original SAM D MCUs – developed by Atmel prior to its acquisition by Microchip – were based on the Cortex-M0+. “But we’ve always wanted to take the product line to the next level of performance. This allows Microchip to address a broader range of consumer and industrial automation applications.” Limited the Clock RateBucking the trend to a certain extent, both Silicon Labs and Microchip have limited the clock rate in their latest MCUs. Giant Geckos, for example, have a maximum clock of 72MHz. “These products are focused on energy efficiency,” Loe claimed. “If you build an MCU to run at 200MHz, for example, then each clock cycle will consume more energy than in an MCU running at 72MHz. A lot of MCUs will be used in battery powered apps, so we need to be energy efficient and to enable the CPU to sleep a lot.” Rangarajan agreed that clock rate is not always the primary factor when it comes to developing MCU portfolios. “We hear our customers saying don’t give me faster clock rates, make sure the MCUs meet my requirements. An app that runs from a battery requires a power efficient MCU. If you want a fast MCU, then you have to make trade offs.” In Loe’s views, MCU selection is all about the ability to perform certain tasks at a particular power efficiency. “That is always going to involve trade offs, but an M4 based MCU will generally be good for embedded applications with challenging energy consumption requirements.” Adopt the Concept of Smart PeripheralsBoth companies have adopted the concept of smart peripherals in their recent products. Loe explained: “Twenty years ago, most MCUs saw the CPU doing everything. That took a lot of CPU cycles, which meant you couldn’t do as much as you might have liked.“Today, most apps will take advantage of DMA, which offloads the CPU. In turn, this allows the CPU to do more.” Rangarajan said Microchip provides what he called ‘sleepwalking’ peripherals. “If there’s a requirement for them to do small numbers of transactions, this can be done without waking the CPU.” On the other hand,Sillicon Loe Noted that It’s all about when you have to wake up the M4 core. We’re trying to allow it to sleep for as much as possible. More than half of the peripherals in a Giant Gecko can run autonomously in deep sleep mode. Both Companies are Keen to Highlight Their Provision Silicon Labs has launched a starter kit to support Giant Gecko based application development(following picture) With this approach, a Giant Gecko’s A/D converter can operate while the CPU is in deep sleep mode. “It can sample and use DMA to pull the data into RAM,” Loe continued.Loe highlighted a couple of aspects. “We have included a cyrotimer that runs in shut off; the lowest energy mode. It’s a simple timer that’s useful when you need the CPU to be asleep for minutes. there’s the Peripheral Reflex System, which allows peripherals to talk. For example, the real time clock could tell the A/D converter to take a sample. It gives a level of determinism which you don’t get from a CPU.  Microchip's Product brings better power efficiency How does an MCU developer differentiate their products from similar devices with an M4 core? Rangarajan pointed to the integration of a buck regulator. “This brings better power efficiency,” he claimed, “which means lower active power consumption; as little as 65µA/MHz. The parts also support flexible pin options.”“We’re offering the best integrated security features,” Rangarajan contended. “SAM Dx/Ex MCUs have crypto hardware acceleration – symmetrical and asymmetrical – and public key encryption, amongst other features. It’s something Microchip has taken to heart and has made sure it’s all in the MCU.“We’re offering the best integrated security features,” Rangarajan contended. “SAM Dx/Ex MCUs have crypto hardware acceleration – symmetrical and asymmetrical – and public key encryption, amongst other features. It’s something Microchip has taken to heart and has made sure it’s all in the MCU.  EndLoe pointed to the security management unit (SMU) as an ‘upgrade’ to the memory protection unit (MPU) associated with the M4’s core. “While the MPU allows you to segment memory into eight regions, the SMU takes that further. The MPU is restricted to eight regions, so there is limited granularity. The SMU allows you to selectively say which pieces of code can access each peripheral.” “All of this is important,” Rangarajan concluded, “as security will become standard in the next few years.” 

The simplest semiconductor component, the diode, has an astonishing number of applications that are enabled by a number of practical and unique types of diodes that are vital in modern electronics.Now let's get start to learn about diodes.   Applications of Diodes While only two pin semiconductor devices, there are a number of applications of diodes that are vital in modern electronics. Diodes are known for only allowing current to move in one direction through the component.   This lets a diode acts as a one-way valve, keeping signals where they need to be or routing them around components. While diodes only let current move in one direction, each type of diode acts differently, making a number of useful applications for diodes.   Some of the typical applications of diodes include:   ·  Rectifying a voltage, such as turning AC into DC voltages ·  Isolating signals from a supply ·  Voltage Reference ·  Controlling the size of a signal ·  Mixing signals ·  Detection signals ·  Lighting ·Lasers diodes   Power Conversion One significant application of diodes is to convert AC power to DC power. A single diode or four diodes can be used to transform 110V household power to DC by forming a half-way (single diodes) or a full-wave (four diodes) rectifier. A diode does this by allowing only half of the AC waveform to travel through it. When this voltage pulse is used to charge a capacitor, the output voltage appears to be a steady DC voltage with a small voltage ripple.   Using a full wave rectifier makes this process even more efficient by routing the AC pulses so both the positive and negative halves of the input sine wave are seen as only positive pulses, effectively doubling the frequency of the input pulses to the capacitor which helps keep it charged and deliver a more stable voltage. Diodes and capacitors can also be used to create a number of types of voltage multipliers to take a small AC voltage and multiply it to create very high voltage outputs. Both AC and DC outputs are possible using the right configuration of capacitors and diodes.   Demodulation of Signals The most common use for diodes is to remove the negative component of an AC signal so it can be worked with easier with electronics. Since the negative portion of an AC waveform is usually identical to the positive half, very little information is effectively lost in this process. Signal demodulation is commonly used in radios as part of the filtering system to help extract the radio signal from the carrier wave.   Over-Voltage Protections Diodes also function well as protection devices for sensitive electronic components. When used as voltage protection devices, the diodes are non-conducting under normal operating conditions but immediately short any high voltage spike to ground where it cannot harm an integrated circuit. Specialized diodes called transient voltage suppressors are designed specifically for over-voltage protection and can handle very large power spikes for short time periods, typical characteristics of a voltage spike or electric shock, which would normally damage components and shorten the life of an electronic product.   Current Steering The basic application of diodes is to steer current and make sure it only flows in the proper direction. One area where the current steering capability of diodes is used to good effect is in switching from power from a power supply to running from a battery. When a device is plugged in and charging, for example, a cell phone or uninterruptible power supply, the device should be drawing power only from the external power supply and not the battery and while the device is plugged in the battery should be drawing power and recharging. As soon as the power source is removed, the battery should power the device so no interruption in noticed by the user.   Ref. MN3306 MURB1520 SBG1030L-T-F