The Kynix Blog

IntroductionA stable power supply is necessary for normal operation of the electrical system. Except for the use of solar cells or chemical batteries in certain special occasions, the direct current of most circuits is converted from the alternating current of the grid. The bridge rectifier is commonly used to convert AC into DC, which is the most commonly used circuit that uses the unidirectional conductivity of diodes for rectification. There are many types of bridge rectifiers: flat, round, square, bench-shaped (plug in and SMD), etc., having GPP and O/J structures. The maximum rectified current ranges from 0.5A to 100A, and the maximum reverse peak voltage ranges from 50V to 1600V.What is Bridge Rectifier?CatalogIntroductionⅠ Bridge Rectifier Diode CircuitⅡ Bridge Rectifier Circuit FeaturesⅢ Single Phase Rectification vs Three Phase Rectification3.1 Single Phase Bridge Rectifier Circuit3.2 Three Phase Bridge Rectifier CircuitⅣ Role of Bridge RectificationⅤ Bridge Rectifier Wiring DiagramⅥ Difference between Bridge Rectifier and Full-wave Rectifier CircuitⅠ Bridge Rectifier Diode CircuitThe bridge rectifier uses four semiconductor diodes to be connected in pairs. When the positive half of the input sine wave is turned on, the two tubes are turned on, and the positive output is obtained; on the contrary, when the negative half of the sine wave is input, the other two tubes are turned on. Since the two tubes are reversely connected, the output is still the positive part of the sine wave. In addition, the utilization efficiency of the input sine wave by the bridge rectifier is twice as high as that of the half-wave rectifier.The rectifier bridge stack is generally used in a full-wave rectifier circuit, and it is divided into a full bridge and a half bridge. The full bridge is composed of 4 rectifier diodes connected in the form of a bridge full-wave rectifier circuit and packaged as a whole. The half bridge is to seal the half of the two diode bridge rectifiers together. Two half bridges can form a bridge rectifier circuit, and a half bridge can also form a full wave rectifier circuit with a center tap of the transformer. When choosing a rectifier bridge, the rectifier circuit and operating voltage must be considered carefully.The forward current of the full bridge has various specifications such as 0.5A, 1A, 1.5A, 2A, 2.5A, 3A, 5A, 10A, 20A, 35A, 50A, etc. The withstand voltage (the highest reverse voltage) is 25V, 50V, 100V, 200V, 300V, 400V, 500V, 600V, 800V, 1000V, etc.In this chapter, the rectifier diode is regarded as an ideal component, that is, its forward conduction resistance is considered to be zero, and its reverse resistance is infinite, because of the convenience of analyzing the rectifier circuit. However, in practical applications, it should be considered that the diode has internal resistance, and the output amplitude of the waveform obtained after rectification will be reduced by 0.6~1V. When the input voltage of the rectifier circuit is large, this part of the voltage drop can be ignored. On the contrary, if the input voltage is small, for example, if the input is 3V, the output is only 2V, and the influence of the diode forward voltage drop needs to be considered.Current Direction of the Bridge Rectifier CircuitFigure 1.In the positive half cycle of u2, D1 and D3 are turned on, D2 and D4 are turned off, and the current returns from the upper end of the TR secondary to the lower end via D1→RL→D3, and a half-wave rectified voltage is obtained on the load RL.In the negative half cycle of u2, D1 and D3 are off, D2 and D4 are on, and the current returns from the lower end of Tr secondary to the upper end of Tr secondary via D2→RL→D4, and the other half-wave rectified voltage is obtained on the load RL. Ⅱ Bridge Rectifier Circuit Features(1) The rectification device used is twice that of full-wave rectification.(2) Rectified voltage pulse changing direction is the same as full-wave rectification.(3) The reverse voltage that each device bears is the peak value of the power supply voltage.(4) The utilization rate of the transformer is higher than that of the full-wave rectifier circuit. Ⅲ Single Phase Rectification vs Three Phase Rectification3.1 Single Phase Bridge Rectifier CircuitFigure 2.The single phase bridge rectifier circuit is composed of four diodes connected in the form of a bridge. Its disadvantage is that it only uses half a cycle of the power supply, and at the same time the rectification voltage has a large pulsation.The above Figure 2 (a) shows the direction of current in the single-phase bridge rectifier circuit. The solid arrow indicates the situation when the AC power supply is in the positive half cycle, and the dotted arrow indicates the situation when the AC power supply is in the negative half cycle.It can be seen that the four diodes are divided into two parts: positive half cycle and negative half cycle. However, the current direction on the load does not change. This is full-wave rectification. In addition, the single-phase bridge rectifier circuit can be implemented with an integrated device "bridge stack" in practice.In Figure 3. shows the waveform diagram of the single phase bridge rectifier circuit. According to the diagram, the average voltage is: Uo ≈ 0.9U2 (where U2 is the effective value of the output voltage of the transformer secondary side).Figure 3. Wave Form (single phase)3.2 Three Phase Bridge Rectifier CircuitFigure 4.The three phase bridge rectifier circuit is developed from a uncontrolled half-wave rectifier circuit, which is essentially a series connection of a set of common cathode and a set of common anode with three semiconductor diodes.In addition, the three phase bridge circuit must have two thyristors turned on at the same time, one in the common cathode area and the other in the common anode area to form a loop.Circuit Analysis LawThe diode with the highest anode potential in the common cathode group is turned on.The diode with the lowest cathode potential in the common anode group is turned on.Circuit Analysis ExamplesFigure 5. t1 ~ t2In the common cathode group, the potential at point U is the highest, and V1 is on.In the common anode group, the potential at point V is the lowest, and V4 is on.The voltage across the load is the line voltage Uuv. Figure 6. t2~t3In the common cathode group, the potential at point U is the highest, and V1 is on.In the common anode group, the potential at point W is the lowest, and V6 is turned on.The voltage across the load is the line voltage Uuw. Figure 7. t3~t4In the common cathode group, the potential at point V is the highest, and V3 is on.In the common anode group, the potential at point W is the lowest, and V6 is turned on.The voltage across the load is the line voltage Uvw.......SummeryIn a full-wave cycle, it can be divided into 6 intervals, each of which is powered by a pair of phase wires to the load.In a full-wave cycle, each diode is turned on for one-third of the time (the conduction angle is 120°).During the 6 periods in a cycle, the voltage of the load can be seen as a periodic change. Ⅳ Role of Bridge Rectification1. Convert the alternating current generated by the alternator into direct current to power the electrical equipment and charge the battery.2. Limit the battery current to flow back to the generator to protect the generator from being burnt out by the reverse current.Figure 8. Bridge Rectifier AC to DC Flow ChartⅤ Bridge Rectifier Wiring DiagramThe bridge rectifier circuit overcomes the shortcomings that the full-wave rectifier circuit requires the transformer secondary to have a center tap and the diode to withstand large reverse voltage, but two diodes are used. With the rapid development of semiconductor devices and low cost today, this shortcoming is not obvious, so bridge rectifier circuits are widely used in practice.It needs to be pointed out that the diode as a rectifier component should be selected according to different rectification methods and load values. If choose improperly, you may not be able to work safely, or even burn the pipe, causing waste.Figure 9. Schematic Diagram of Bridge Rectifier CircuitThe bridge rectifier circuit can also be considered as a kind of full-wave rectifier circuit. The transformer is connected to four diodes according to the method shown in Figure 9. D1～D4 are four identical rectifier diodes connected in the form of a bridge, so they are called bridge rectifier circuits. Using the guiding function of the diode, the secondary output can be directed to the load even in the negative half cycle. It can be seen from the figure that D1 and D2 lead the current through RL from top to bottom during the positive half cycle, and D3 and D4 lead the current through RL from top to bottom during the negative half cycle. In this structure, if the same DC voltage is output, the secondary winding of the transformer needs only half of the winding compared with the full-wave rectification. However, if the same amount of current is to be output, the diameter of the winding should be increased accordingly.Because the output voltage of the rectifier circuit contains larger pulsating components. In order to reduce the pulsation component as much as possible, on the other hand, it is necessary to keep the DC component as much as possible to make the output voltage close to the ideal DC. This measure is filtering. Filtering is usually achieved by using the energy storage effect of capacitors or inductors.Figure 10. Bridge Rectifier Circuit with CapacitorIn this experimental circuit, capacitor filtering is used, that is, a filter capacitor C is connected in parallel with the load resistance RL. The circuit is shown in Figure 11, and the filtered waveform is as shown in the figure below.Figure 11. Full-wave Rectification Filter WaveformThe DC component of the full-wave rectified output voltage (compared to the half-wave) is increased, and the pulsation is reduced, but the transformer needs a center tap, which is troublesome to manufacture, and the rectifier diode needs to withstand high reverse voltage, so it is generally suitable for the low output voltage.Figure 12. Half-wave Rectification Filter WaveformHalf-wave rectification is the most commonly used circuit that uses the unidirectional conductivity of a diode for rectification. Ⅵ Difference between Bridge Rectifier and Full-wave Rectifier Circuit1) Don't need a center tap on the secondary side of the bridge rectifier circuit transformer, but use 2 more rectifier diodes.2) The full-wave rectifier circuit uses less than 2 rectifier diodes, but the secondary side of the transformer should be center-tapped.3) The reverse withstand voltage of the rectifier diode used in the full-wave rectifier circuit is twice that of the bridge rectifier.4) Rectification and full-wave rectification have different requirements for the number of secondary transformers. The former requires only 1 set of coils, while the latter requires 2 sets.5) Rectification and full-wave rectification have different requirements for the secondary current of the transformer, the former is twice the latter. Frequently Asked Questions about Bridge Rectifier Circuit1. What does a bridge rectifier do?A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding. ... Diodes are also used in bridge topologies along with capacitors as voltage multipliers. 2. How does a bridge rectifier convert AC to DC?Bridge rectifiers convert AC to DC using its system of diodes made of a semiconductor material in either a half wave method that rectifiers one direction of the AC signal or a full wave method that rectifies both directions of the input AC. 3. What happens when a bridge rectifier fails?Without capacitor smoothing, when 1 diode fails open in a bridge rectifier, both voltage and current reduce. With capacitor smoothing, when 1 diode fails open in a bridge rectifier, the voltage remains fairly constant but the current increases. 4. Why do we use 4 diodes in bridge rectifier?The bridge rectifier consisting of four diodes enables full wave rectification without the need for a centre tapped transformer. The bridge rectifier is an electronic component that is widely used to provide full wave rectification and it is possibly the most widely used circuit for this application. 5. Why is a bridge rectifier more preferable than a full wave rectifier?Bridge rectifier is driven by a single winding which carries current both cycles in load. ... Full wave is better than bridge in one more aspect i.e. the output DC voltage is slightly higher than bridge. This is because it has only 1 diode drop from AC to DC.

IntroductionPCB exists in every electronic device. A fully functional PCB is mainly used to create connections between components, such as resistors, capacitors, inductors, diodes, transistors, integrated chips, etc. It is the carrier of the entire logic circuit. Sound PCB design can save production costs, and achieve good circuit performance and heat dissipation effect. PCB designs vary in complexity according to product needs. This article mainly talks about wiring, one of the basics of PCB design.PCB Design: From Idea to Schematic to PCBCatalogIntroductionⅠ PCB Basics: Wiring RulesⅡ Three PCB Wiring MethodsⅢ PCB Design: Wire InspectionⅣ Complete PCB Design Projects Inspection4.1 General PCB Design Inspection Projects4.2 PCB Electrical Characteristics Checking Projects4.3 PCB Physical Characteristics Checking Projects4.4 PCB Mechanical Design Factors4.5 PCB Installation Requirements4.6 PCB Pull-out Requirements4.7 PCB Mechanical Considerations4.8 PCB Electrical Considerations4.9 Electronics Inspection Before Into A PCBⅤ ConclusionⅠ PCB Basics: Wiring Rules1. The area within 1mm from the edge of the PCB board and within 1mm around the mounting hole will not take wiring.2. The power line width should not be less than 18mil; the signal line width should not be less than 12mil; the cpu input and output lines should not be less than 10mil (or 8mil); the line spacing should not be less than 10mil.3. It is necessary noted that the power line and the ground line should be as radial as possible, and the signal line must not be looped.4. Ground circuit rulesThe loop area formed by the signal line should be as small as possible. The smaller the loop area, the less external radiation and the less interference from the outside. An example is shown in the figure below:5. Crosstalk controlHere crosstalk refers to the mutual interference caused by long parallel wiring between different networks on the PCB, which caused by the distributed capacitance and inductance between the parallel lines. The main measures to overcome it are:a. Increase the spacing of parallel wiring and follow the 3W rule. To ensure that the distance between the lines is large enough, when the distance between the line and the center of the line is not less than 3 times the line width (as shown in the figure below). If the line center distance is not less than 3 times the line width, 70% of the line electric fields will not interfere with each other, which is called 3W rule.b. Insert a grounded isolation wire between the parallel wires. Reduce the distance between the wiring layer and the ground plane.6. The direction control rules of routing:The routing directions of adjacent layers are orthogonal. Different signal lines in the same direction on adjacent layers should be avoided to reduce unnecessary interlayer crosstalk. When the signal rate is high, use a ground plane to isolate each wiring layer, in other words, isolate each signal line with ground line. The neighbouring wires used in the input and output end of the circuit shouldn’t be parallel to prevent the feedback, and it is best to add a ground wire between these wires.7. Open loop inspection rules for wiring:Generally, it is not allowed to have a floating wiring at one end, because of the "antenna effect" and unnecessary interference radiation and reception, which may bring unpredictable results.8. Impedance matching inspection rulesThe wiring width of the same network should be kept the same. Line width variations will bring uneven line characteristic impedance, and reflection will occur when the transmission speed is high. This situation should be avoided in the design. Under certain conditions, such as the lead wires of the connector and the similar structure of the lead wires of the BGA package, the change of the line width may not be avoided, so that the length of the middle inconsistent part should be minimized.9. Wiring closed loop inspection rules:Prevent signal lines from forming self-loops between different layers. Such problems are prone to occur in multilayer board design, and it will cause radiation interference. As shown below:10. The branch length control rule of wiring:Try to control the length of branches, and the general requirement is Tdelay≤Trise/20.11. Resonance rules of wiring:For high-frequency signal design, the wiring length must not be an integer multiple of its wavelength to avoid resonance.12. Line length control rules:In fact, it refers to the short-circuit rule. When designing, you should keep the wiring length as short as possible to reduce interference problems caused by unnecessary lines. Especially for some important signal lines, such as clock lines, be sure to place oscillators close to the device. In the case of driving multiple devices, the network topology should be decided according to the specific situation.13. Parallel input and output wires on the PCB board should be avoided as far as possible to avoid parallel. It is best to place a ground wire between the two wires to avoid circuit feedback coupling.14. Digital ground and analog ground should be separated. For low-frequency circuits, single-point parallel grounding should be used. High-frequency circuits should be grounded in series with multiple points. For digital circuits, the ground wire should be closed into a loop to improve anti-noise capability.15. The wiring and via distribution of the whole circuit board should be uniformity. When the outer signal of the circuit board has a large blank area, auxiliary lines should be added to make the lines distribution on the board basically balanced.16. The low-frequency circuit can be grounded at a single point in parallel, and the actual wiring can be connected in series and then grounded in parallel. The high-frequency circuit can be grounded in series with multiple points. The ground wire should be short and thick. For high-frequency components, a large area ground foil can be used. The ground wire should be as thick as possible. If the ground wire is a very thin, the ground potential will change with the current, which reduces the noise resistance.17. Multilayer boards should be as symmetrical as possible when designing the laminated structure, as well as the wiring density and copper layout of each layer to reduce warpage and reduce EMI during soldering.18. The signal line should not cross the power supply and ground. The signal reference plane should be as complete as possible.19. Impedance controlThe signal lines that need impedance control must be wired in strict accordance with the calculated data, in addition, it is necessary to tell manufacturers it. For signal lines that do not require it, the impedance should be calculated to prevent unnecessary interference.20. Grid copper should be used less in low frequency circuits. Although it can effectively reduce the problem of large area copper skin blistering. When using grid copper, you need to consider the electrical length of the grid line and the working frequency of the circuit board. If using grid copper, the power supply should also be coated with solid copper as much as possible.21. A group of buses with the same attribute should be wired side by side as much as possible, and the length should be as equal as possible. Ⅱ Three PCB Wiring MethodsThe wires should take the shortest route between components according to the specified wiring rules. Limit the coupling between parallel wires as much as possible. Good PCB design requires the minimum number of wiring layers, and also requires fair use of the widest wire and the largest pad size corresponding to packaging density. For example, rounded corners and smooth inner corners design may avoid some electrical and mechanical problems, therefore, sharp corners and sharp corners in the wire should be avoided. Here introduces three main PCB routing methods; right-angle wiring, differential wiring, and serpentine wiring to illustrate PCB layout:A. The influence of right-angle wiring on the signal is mainly reflected in three aspects:1. The corner can be equivalent to the capacitive load on the transmission line to slow down the rise time.2. Discontinuous impedance will cause signal reflection.3. The EMI generated by the right-angle tip reaches the RF field above 10GHz. Such a right-angle is likely to develop into the source of high-speed problems. B. To figure out what is differential wiring, you must first understand what is differential signal. In a word, the driving end sends two equal and inverted signals, and the receiving end judges the logic state "0" or "1" by comparing the difference between the two voltages. The pair of traces carrying differential signals is called differential traces. Compared with ordinary single-ended signal traces, differential signals have the most obvious advantages in the following three aspects:1. Have Strong anti-interference ability. Because the coupling between the two differential traces occurs, when there is noise interference from the outside, they are almost coupled to the two lines at the same time. However, the receiving end only cares about the difference between the two signals. Therefore, the external common mode noise can be completely canceled.2. It can effectively suppress EMI. Due to the opposite polarity of the two signals, the electromagnetic fields radiated by them can cancel each other out. What’s more, the tighter the coupling, the less the electromagnetic energy leaked to the outside world.3. The timing positioning is accurate. Because the switch change of the differential signal is located at the intersection of the two signals. Unlike ordinary single-ended signals, which rely on the high and low threshold voltages to judge. Timing positioning is less affected by the process and temperature, and also more suitable for circuits with low amplitude signals. The current popular LVDS (low voltage differential signaling) refers to this small amplitude differential signaling technology. C. Serpentine line is a type of wiring method often used in PCB layout. Its main purpose is to adjust the delay to meet the system timing design requirements. The two most critical parameters are the parallel coupling length (Lp) and the coupling distance (S). Obviously, when a signal is transmitted on a serpentine trace, the parallel line segments will be coupled in a differential mode. The smaller the S, the greater the Lp, the greater the coupling. It may cause the transmission delay to be reduced, also the signal quality is greatly reduced due to crosstalk. The mechanism can refer to the analysis of common mode and differential mode crosstalk. The following are some suggestions when dealing with serpentine wring:1. Try to increase the distance (S) of parallel lines, at least more than 3H(H refers to the distance from the signal trace to the reference plane). As long as S is large enough, the mutual coupling effect can be almost completely avoided.2. Reduce the coupling length Lp. When the double Lp delay approaches or exceeds the signal rise time, the crosstalk generated will reach saturation.3. The signal transmission delay caused by the strip-line or embedded micro-strip line is less than that of the micro-strip. Theoretically, the strip-line will not affect the transmission rate due to differential mode crosstalk.4. For signal lines with high-speed and strict timing requirements, try not to take serpentine lines, especially in a small area.5. You can often use s-shaped routing at any angle, which can effectively reduce the mutual coupling.6. In high speed, the serpentine line has no ability so-called filtering or anti-interference, and can only reduce the signal quality, so it is better to use for timing matching.7. Sometimes you can consider the spiral routing method for winding. Simulation shows that its effect is better than normal serpentine routing.Ⅲ PCB Design: Wire Inspection1.Wire SpacingThe minimum spacing of wires must be determined to eliminate voltage breakdown or arcing between adjacent wires. The spacing is variable, it mainly depends on the following factors:1) Peak voltage between adjacent wires2) Atmospheric pressure (maximum working altitude)3) Coating layer4) Capacitive coupling parametersComponents with critical impedance or high-frequency components should be placed very close to reduce the critical stage delay. There is something need to pay attention to. Transformers and inductive components should be isolated to prevent coupling. Inductive signal wires should be laid orthogonally at right angles. Components that generate any electrical noise due to magnetic field movement should be isolated or rigidly installed to prevent excessive vibration.2. Whether the wire is short and straight without sacrificing function.3. Whether the restrictions on the wire width are complied with.4. There must be a minimum distance between wires, wires and mounting holes, wires and pads.5. Whether to avoid all the wires (including component leads) closer to parallel wiring.6. Whether sharp corners (≤90℃) are avoided in the wire pattern. Ⅳ Complete PCB Design Projects Inspection4.1 General PCB Design Inspection Projects1) Has the circuit been analyzed? Is the circuit divided into basic units to smooth the signal?2) Does the circuit allow short or isolated key leads?3) Where must be shielded, are they effectively shielded?4) Have you made full use of the basic grid graphics?5) Is the best size of the printed circuit board?6) Do you use the available wire width and spacing as much as possible?7) Has the preferred pad size and hole size been used?8) Are the base plate and the sketch consistent?9) Is less cross-wiring used? Do cross wires pass through components and accessories?10) Are the letters visible after assembly? Are their size and model correct?11) In order to prevent blistering, is there any window on the large area of copper foil?12) Are there tool positioning holes?4.2 PCB Electrical Characteristics Checking Projects1) Have you analyzed the influence of wire resistance, inductance, and capacitance, as well as the critical voltage drop on the ground?2) Does the wire spacing and shape meet the insulation requirements?3) Has the insulation resistance value been controlled and specified in key areas?4) Is the polarity fully recognized?5) According to geometric view, has the effect of wire spacing on leakage resistance and voltage been measured?6) Has the medium for changing the surface coating been identified?4.3 PCB Physical Characteristics Checking Projects1) Are all pads and their positions suitable for final assembly?2) Can the assembled PCB meet the shock and vibration conditions?3) What is the required spacing of standard components?4) Are the components that are not firmly installed or the heavier parts fixed?5) Is the heating element heat dissipation and cooling normally? Or is it isolated from the printed circuit board and other heat-sensitive elements?6) Are the voltage divider and other multi-lead components placed correctly?7) Is the arrangement and orientation of components easy to check?8) Has it eliminated all possible interference on the printed circuit board?9) Is the size of the positioning hole correct?10) Are the tolerances complete and reasonable?11) Have you controlled and signed the physical properties of all coatings?12) Is the ratio of via hole and lead diameter within an acceptable range?4.4 PCB Mechanical Design FactorsThe printed circuit board adopts mechanical methods to support the components, however, it cannot be used as an unique structural part of the entire device. On the edge of the printing plate, at least every 5 inches for a certain support. The factors that must be considered when selecting and designing printed circuit boards are as follows:1) The size and shape of the printed circuit board.2) The type of mechanical accessories and plug (seat) required.3) The environmental adaptability of circuits.4) According to some factors, such as heat and dust, install the printed circuit board vertically or horizontally.5) Some environmental factors that require special attention, such as heat dissipation, ventilation, shock, vibration, and humidity, dust, and radiation, etc.6) Physical support7) Install and fix.8) Disassemble4.5 PCB Installation RequirementsAccording to practical experience, the distance between the supporting points of a printed circuit board with a thickness of 0.031-0.062 inches should be at least 4 inches. For a printed circuit board with a thickness greater than 0.093 inches, the distance between the supporting points should be at least 5 inches. Taking this measure can improve the rigidity of the printed circuit board and avoid possible resonance. The following factors should be considered before deciding which mounting technology they use.1) PCB structure.2) Input and output terminals.3) Available equipment space.4) Convenience of loading and unloading.5) Type of attachments.6) Required heat dissipation.7) Required shieldability.8) The type of circuit and its relationship with other circuits.4.6 PCB Pull-out Requirements1) The influence of plugging tools on the installation distance between two printed circuit boards.2) When the plug-in tool used in the equipment, its size should be considered.3) A plug-in device is required, which is usually fixed to the printed circuit board assembly with rivets.4) As for the mounting frame of the printed circuit board, special design such as load bearing flange is required.5) The adaptability of the plug-in tool used and the size, shape and thickness of the printed circuit board.4.7 PCB Mechanical ConsiderationsThe characteristics of the board substrate that have an important influence on the printed circuit assembly are: water absorption, thermal expansion coefficient, heat resistance, flexural strength, impact strength, tensile strength, shear strength and hardness. All these characteristics affect the function and the production efficiency of the printed circuit board structure. For most applications, the dielectric substrate materials of the printed circuit board are as following:1) Phenolic impregnated paper2) Acrylic-polyester impregnated randomly arranged glass mat3) Epoxy impregnated paper4) Epoxy impregnated glass clothEach substrate can be flame retardant or combustible. The first 3 types mentioned above can be processed. The most common used material for printed circuit boards with metalized holes is epoxy-glass cloth. Its dimensional stability is suitable for high-density circuits and can minimize the occurrence of cracks in the metalized holes. One disadvantage of epoxy-glass cloth laminate is that it is difficult to punch in the usual thickness range of printed circuit boards. For this, all holes are usually drilled and copied and milled to form a print shape of the circuit board.4.8 PCB Electrical ConsiderationsIn DC or low-frequency AC applications, the most important electrical characteristics of insulating substrates are: insulation resistance, anti-isolation, printed wire resistance, and breakdown strength. In high frequency and microwave applications, include: dielectric constant, capacitance, and dissipation factors. In all applications, the current carrying capacity of printed wires is important.4.9 Electronics Inspection Before Into A PCB1) Check the rationality and correctness of the schematic diagram.2) Check the correctness of the component packaging of the schematic.3) The distance between strong and weak current lines, and the distance between isolation areas.4) Check the schematic diagram and PCB diagram to prevent the loss of the network table.5) Whether the package of the component matches the physical object.6) Whether the placement of the components is appropriate.7) Whether the components are easy to install and disassemble.8) Whether the temperature sensitive element is too close to the heating element.9) Whether the distance and direction of the mutual inductance components are appropriate.10) Whether the placement between the connectors is smooth.11) Easy to plug in and plug out12) Input and output13) Strong current and weak current14) digital and analog should be interlaced.15) Arrangement of elements on the upside and downside16) Check whether the directional component has been wrong flipped instead of rotated.17) Check whether the mounting holes of the component pins are suitable and whether it is easy to insert.18) Check whether the empty pin of each component is normal and whether it is a missing line.19) Check whether there are vias between the upper and lower wiring of the same net table. And the pads are connected through the holes, to prevent disconnection and ensure the integrity of the circuit.20) Silk screen printing should be clear, so that the operation of welding or maintenance can be easy.21) The arrangement of power and signal lines in the socket should ensure signal integrity and anti-interference.22) Pay attention to the proper ratio of pads and solder holes.23) Each plug should be placed on the edge of the PCB board as much as possible and easy to operate.24) Whether the size and distribution of the mounting holes on the PCB are appropriate to reduce the PCB bending stress.25) Pay attention to the height distribution of the components on the PCB to ensure easy assembly.Ⅴ ConclusionBased on the above mentioned rules, drawing the PCB schematics you need becomes easier. Decide what PCB you want to and install a PCB design software. PCB software is really helpful and powerful. Also a software can check your design to make sure the design does not contain errors such as traces that incorrectly touch, traces too skinny, or drill holes that are too small. For example, run the Electrical Rules Checker (ERC) to see if you’ve made any typical errors. There is less thing stopping you from making your first PCB, right? Frequently Asked Questions about PCB Design Diagram1. Which side of PCB is correct for soldering?The bottom side of the PCB is usually the side without components and the side that touches the solder wave during assembly. That is why sometimes it is also called SOLDER side. However more often, PCB are populated on both sides and the assembly process does not require wave soldering. 2. Which soldering method is suitable for soldering printed circuit board?Soldering Iron – Used to melt solder and connect component pins to board pads. A cheap soldering pencil may be sufficient, but a temperature-controlled solder station is best for high performance boards. Solder – An alloy of tin and lead with a low melting point. 3. What is PCB diagram?A PCB schematic is a simple two-dimensional circuit design showing the functionality and connectivity between different components. ... Once the blueprint has been completed, the PCB design comes next. The design is the layout, or physical representation of the PCB schematic and includes the copper track and hole layout. 4. Why we use PCB in soldering?PCB soldering is another term for the process of soldering electrical circuit boards. ... As the soldering iron melts this metal, it is then used a bit like glue to stick to pieces together. As the solder metal cools, it will re-harden into one large shape that connects the two parts. 5. How do you read a PCB board?Start with an easy analog circuit, such as a guitar distortion pedal, and work your way up to more complicated versions. Make a drawing of the top of the circuit board. Show the positions of the capacitors, integrated circuits, resistors, transistors and other components. Review it to make sure everything is included.

IntroductionAlarm Circuits and Control Circuits are pretty common in daily life. A control circuit is a special type of circuit used to control the operation of a completely separate power circuit. Alarm circuit is a security circuit to reduce life loss and poverty under the excepted prevailing conditions. Both are quite famous and you probably could have seen plenty of different versions of them. Here, we will introduce several available home/office hobby circuits for smoking alarm, temperature controlling and timing, with their design principles, and component selection. They will provide more convenience for your daily life.A Simple Guide to Electronic Components in CircuitsCatalogIntroductionⅠ Indoor Monitoring Circuit DesignⅡ Smoke Alarm Circuit DesignⅢ Temperature Controlled Circuit Using NE555Ⅳ Temperature Sensor Circuit for Temp MeasuringⅤ Water Tank Temperature Controlled ProjectⅥ Cyclic Timing Circuit DiagramⅦ Indoor Overvoltage Protection Circuit DesignⅧ Temperature Fan Controller DiagramⅨ Water Boiling Alarm Circuit DesignⅩ FAQEvery alarm circuit and control circuit is composed of a number of basic components connected together to achieve the desired performance. The following lists some common and simple alarm and control circuits diagrams to share different ideas for protecting your home/office and making your life more easier.Ⅰ Indoor Monitoring Circuit DesignThe monitor can detect infrared rays emitted by the human body, and when a person enters the monitoring area, it can sound for alarm. It is suitable for homes, offices, warehouses, laboratories and other important occasions.👍 Circuit Working ModelFigure 1. Infrared Detection Alarm CircuitThe device consists of an infrared sensor, a signal amplifier circuit, a voltage comparator, a delay circuit and an audio alarm circuit. When the sensor IC1 detects the infrared signal radiated by the human body in front, it outputs a weak electrical signal from the pin②. It is amplified by the first-stage amplifying circuit formed by the transistor VT1, and then input to the operational amplifier IC2 through C2 with high gain and low-noise amplification. IC3 acts as a voltage comparator. Its pin⑤ reference voltage is provided by R10 and VD1. When the signal voltage output by IC2 pin① pass to the IC3 pin⑥, the voltages of the two input terminals are compared. At this time, IC3 pin⑦ changes from the high level to the low level. IC4 is an alarm delay circuit, formed by R14 and C6. Its continuous time is about 1 minute.When IC3 pin⑦ becomes low level, C6 discharges through VD2, IC4 pin② becomes low level,  which is compared with IC4 pin③ reference voltage. When it is lower than its reference voltage, IC4 pin① changes to high level, VT2 is turned on, and the buzzer BL is powered on and emits an alarm sound. After the infrared signal of the humans disappears, IC3 pin⑦ outputs to high level, and VD2 is cut off at this time. Since the voltage at both ends of C6 cannot change suddenly, charge C6 slowly through R14. When the voltage at both ends of C6 is higher than its reference voltages, IC4 pin① becomes low level for about 1 minute. That is, the alarm time lasts for 1 minute.The power-on delay circuit is composed of VT3, R20, and C8. It is mainly to prevent alarming immediately when powering on, so that the user has enough time to leave the monitoring site, and at the same time can prevent a false alarm occurred during a power cut. The device uses 9-12V DC power supply, with T step-down, full-bridge rectification, and C10 filtering. The detection circuit uses IC5 for power supply, and automatic non-stop conversion with AC and DC. 👉 Components SelectionIC1 adopts imported device Q74, the wavelength is 9~10um. IC2 uses op-amp LM358, which has high gain and low power consumption. IC3 and IC4 are dual voltage comparators LM393 with low power consumption and low offset voltage. Among them, C2 and C5 must use tantalum capacitors with small drain electrodes, otherwise the debugging will be affected. R12 is the key element to adjust sensitivity, and linear high-precision sealed type should be selected. Other components can be selected as shown in the circuit diagram. 👉 DIY and AdjustmentWhen making, a Fresnel lens is installed in front of the IC1 sensor. Since the frequency range of the human body is 0.1~10Hz, it is necessary to use the Fresnel lens to multiply the frequency of the human body. After installation finished, connect the power supply for debugging. Let a person walk about 7-10m in front of the detector, adjust R12 in the circuit, and make the buzzer alarm. As long as the other parts are of good quality and welded correctly, they can work normally without debugging. The static working current of this machine is about 10mA. It will enter the waiting state about 1 minute after the power is turned on. As long as someone enters the monitoring area, it will alarm, and stops in 1 minute. In addition, if the buzzer is changed to a relay to drive other devices, it will be used for other controls. Ⅱ Smoke Alarm Circuit DesignThis smoke alarmer can be used in family rooms or various places where smoking is forbidden (such as hospitals, conference rooms, etc.). When someone smokes, the no-smoking warning device will emit a warning sound of "No Smoking!" to remind the smoker to stop smoking consciously.👍 Circuit Working ModelFigure 2. Smoke Alarm CircuitThe no-smoking warning circuit is composed of a smoke detector, a monostable trigger, a voice generator and a power amplifier circuit. The smoke detector consists of potentiometer RP1, resistor R1 and gas sensor. The monostable trigger has time-base integrated circuit IC1, resistor R2, capacitor C1, and potentiometer RP2. The voice generator circuit is composed of voice integrated circuit IC2, resistors R3-R5, capacitor C2 and Zener diode VS. The audio power amplifier circuit includes transistor V, boost power amplifier module IC3, resistors R6 and R7, capacitors C3 and C4, and speaker BL.When the gas sensor doesn’t detect smoke, the resistance value between A and B is relatively large. IC1 pin2 is high level (higher than 2VCC/3), pin3 outputs low level, while voice generator circuit and the audio power amplifier circuit does not work. When someone smokes and the gas sensor detects the smoke, the resistance value between the A and B becomes smaller, causing the voltage of IC1 pin2 to drop. When the voltage of this pin drops to VCC/3, IC1 pin3 changes from low level to high level. Pass through current limiter R3, filter C2 and Zener diode VS, the high level will generate 4.2V DC voltage, which is supplied to voice IC2 and crystal arm. After IC2 energizes and works, it outputs a voice electrical signal. After the signal is amplified by V and IC3, it makes BL to emit a voice warning sound of "No Smoking!" 👉 Components SelectionRl~R7 selects 1/4W carbon film resistor or metal film resistor for use. RP1 and RP2 can choose small linear potentiometer or variable resistor. C1, C2 and C4 all use aluminum electrolytic capacitors with a withstand voltage of 16V; C3 uses monolithic capacitors. VS selects the silicon Zener diode of 1/2W, 4.2V for use. V uses S9013 or C8050 silicon NPN transistors. IC1 uses the NE555 timer IC; IC2 uses the voice integrated circuit; lC3 uses the WVH68 boost power amplifier thick-mode IC. BL selects 8Ω, 1~3W electrodynamic speakers. The gas sensor is MQK-2 type sensor. 👉 DIY and AdjustmentThis no-smoking warning device can be used as a smoke alarm to detect fires or harmful gases, and combustible gases. Adjusting the RP1 resistance can change the heating current of the gas sensor (usually about 130mA). And adjusting the RP2 resistance can change the sensitivity of the monostable trigger circuit. Ⅲ Temperature Controlled Circuit Using NE555This circuit is an automatic temperature controller composed of a 555 timer IC and a few peripheral components. Because the voltage at each point in the circuit comes from the same DC power supply, it does not need a high-performance regulated one. Using the capacitor step-down method can work reliably. The circuit components are low in price, small in size, and easy to self-made under amateur conditions. The automatic temperature controller made by this circuit can be used for electric heating control in industrial production and household use, with good effect.👍 Circuit Working ModelFigure 3. 555 Timer Based Circuit for Temperature ControlWhen the temperature is low, the resistance of the thermistor Rt with a negative temperature coefficient is large, the potential of pin2 of the 555 timer IC is lower than 1/3 of the voltage of Ec (about 4V), and its pin3 output high level. At this time, V conducts, the heater RL is heating, and the timing cycle starts. When the temperature of the thermistor Rt is higher than the set value and the timing cycle has not been completed, the heater RL will cut off after the timing cycle stops. When the Rt temperature drops below the set value, V will conduct again and turn on the heater RL for heating. In this way, automatic temperature control can be achieved. 👉 Components SelectionIn this circuit, the thermistor Rt can be a negative temperature coefficient type MF12 or MF53, or other types of negative temperature coefficient thermistors with different resistance values, as long as Rt＋VR1= 2R4 is satisfied under the temperature condition to be controlled. A larger potentiometer VR1 can have a larger adjustment range, but its sensitivity will decrease. The bidirectional thyristor V can also be selected according to the size of the load current. There are no special requirements for other components. Choose according to the parameters given in the circuit diagram. 👉 DIY and AdjustmentThe whole circuit can be installed on PCB. Generally, debugging is not required. The time interval is 1... .1R2×C3, which should be smaller than the thermal time constant of the heating system, but not too small, otherwise it will cause excessive radio frequency interference due to the thyristor V turns on or off rapidly. After installation and debugging, it can be put into a small plastic box, and the thermistor Rt can be led to the required place. Ⅳ Temperature Sensor Circuit for Temp MeasuringThis circuit is a thermometer made by AD590 special integrated temperature sensor, which has the characteristics of simple structure, reliable use and high precision.👍 Circuit Working ModelFigure 4. Digital Thermometer CircuitAfter the 100V AC voltage passes through the transformer T1, the rectifier bridge stack UR and the capacitor C1, the DC voltage is obtained, and then the adjustable voltage regulator circuit μA723C provides a stable working voltage for the temperature sensor AD590. AD590 is a new type of current output temperature sensor, composed of multiple transistors and resistors with the same parameters. When a specific DC working voltage is applied to both ends of the sensor, if the sensor temperature is 1 degree Celsius, the output current of the sensor changes by 1 μA. The changing current of the sensor is converted into a voltage signal through the resistor R5 and the variable resistor RP2, and then output to the digital meter, which displays the temperature change. 👉 Components SelectionThe IC selects AD590-series temperature sensor. There are no special requirements for other components of this circuit, and can be selected according to the parameters given in the circuit diagram. 👉 DIY and AdjustmentBy adjusting the value of resistor R5 and variable resistor RP2, the sensitivity of the circuit output can be improved. Ⅴ Water Tank Temperature Controlled ProjectAn automatic fish tank water temperature controller uses a negative temperature coefficient thermistor as a temperature sensor to automatically heat the fish tank through heating gas. The transient time of this circuit is small, which is beneficial to the accuracy of temperature control. And it is suitable for various sizes of fish tanks.👍 Circuit Working ModelFigure 5. Automatic Control of Fishbowl Water TemperatureAfter being rectified by diodes VD2~VD5 and filtered by capacitor C2, a voltage of about 12V is provided to the control part of the circuit. 555 timer is connected as a monostable flip-flop, the transient state is 11s. Set the control temperature to 25ºC, adjust the potentiometer RP, to get RP + Rt = 2R1 ( Rt is the thermistor with negative temperature coefficient). When the temperature is lower than 25ºC, the Rt resistance value increases, and the pin2 of the 555 timer is low level, then the pin3 output changes from low level to high level. The relay K is turned on, and its contact is closed. The heating tube starts to heat until the temperature returns to 25ºC, the Rt resistance value becomes smaller, the pin2 of the 555 timer is at high level, and the pin3 outputs low level. The relay K loses power, its contact is open, and the heating stops. 👉 Components SelectionIC uses NE555, NA555, SL555 and other 555 timer ICs; VD1 uses IN4148 silicon switching diodes; LED uses common light-emitting diodes; VD2~VD5 uses IN4001 silicon rectifier diodes; Rt uses 470Ω MF51-type negative temperature coefficient thermistors at room temperature; RP uses WSW organic solid trimming potentiometer; R1and R2 uses RXT-1/8W carbon film resistors; C1 and C3 uses CD11-16V electrolytic capacitors; C2 uses CT1 ceramic dielectric capacitors; K uses 12V JZC-22F electromagnetic relay. 👉 DIY and AdjustmentThe temperature sensor probe connects the thermistor Rt with wires, and then seals the solder joint with epoxy glue, to avoid water erosion. As long as the circuit is correct in the DIY process, this circuit is easy to operate. If the component performance is good, it can be used without debugging after installation. Ⅵ Cyclic Timing Circuit DiagramThe circuit can set the cycle time of the equipment and each time it works, allowing the equipment to work continuously according to the set time. This circuit can be applied to control occasions such as timing pumping, timing ventilation, and timing cut off.👍 Circuit Working ModelFgiure 6. Cycle Timing CircuitAfter the circuit is stepped down through the capacitor C2 and the bleeder resistor R3, and then rectified by the bridge stack IC2, and stabilized by VD2, a DC voltage of about 12V is obtained to supply power to IC1 and other circuits. IC1 is a 14-bit binary counter/frequency divider integrated circuit. A clock oscillator with a certain frequency is formed by the internal circuits of R1, R2, C1 and IC1 to provide clock pulses for timing IC1. When the circuit is powered on, it first enters the working gap waiting time of the device. IC1 internally realizes the delay by counting and dividing the clock pulse.  When the timing is up (according to the parameters in the figure, about 3 hours), the Q14 terminal of IC1 outputs high level, making the transistor V conducts. The relay KA gets to work, and drives the controlled equipment to start working. At this time, IC1 starts to count the working time of the device again. When the timing expires (according to the parameters in the figure, about 20 minutes), the Q14 terminal outputs low level. So that V is cut off and the device stops working. And meanwhile, IC1 automatically resets and starts the next timing. So that the device can perform timing cycle according to requirements. In the figure, VL is a working indicator. 👉 Components SelectionIntegrated circuit IC1 chooses 14-bit binary counter/frequency divider CD4066, or CC4066 or other digital circuit integrated blocks with the same function. IC2 selects a 1A, 50V bridge stack, or can be connected with four 1N4007 diodes. Transistor V uses NPN-type transistor 8050, and other transistors such as 9013 or 3DG12 can also be used. VD1 selects rectifier diode 1N4007; VD1 selects 1W, 12V silicon regulator tube, such as 1N4742; VD3 ~VD5 use switching diodes 1N4148; VL selects ordinary light-emitting diodes. Resistors R1, R2, R4, R6 and R7 use 1/4W metal film resistors; R3 and R5 use 1/2W carbon film resistors. C1 selects polyester or monolithic capacitors; C2 selects polypropylene capacitors with a withstand voltage of 450V and above; C3 selects aluminum electrolytic capacitors with a withstand voltage of 16V. Relay KA chooses a miniature relay with a coil voltage of 12V, and the contacts capacity is determined according to the power of the controlled device. 👉 DIY and AdjustmentAfter the circuit is installed, it can work normally without debugging. When you need to adjust the control time, you can adjust the parameters of R1, and C1. Also you can change the position of the IC1 output control terminal (Q4 ~Q14). Ⅶ Indoor Overvoltage Protection Circuit DesignBecause the instability of the mains, the household appliances often affected, their service life may reduce. In serious cases, it is easy to burn out due to voltage surge. The circuit described in this example can solve this problem well.👍 Circuit Working ModelFigure 7. Overvoltage Protection Circuit for AppliancesThe mains supply provides a stable 12V working voltage for the switch integrated circuit via C1, VD1, and DW1. VD3, R2 and RP1 form a voltage divider sampling circuit. When the mains voltage is normal, DW2 cannot be turned on, the working voltage of TWH8778 pin⑤ is lower than 1.6V. The relay J does not pull in, and the mains supplies the CZ socket through the J-1 normally closed contact. When the mains voltage is high than the normal setting, DW2 breaks down, the potential of TWH8778 pin⑤ rises to 1.6V, causing the IC to flip, pin ③ outputs high level. At this time, the relay is pulled in, and the electrical power supply is immediately cut off, avoiding the overvoltage affects electrical appliances. 👉 Components SelectionC1 uses 0.47µ/400V electrolytic capacitor, relay J uses 6V DC contactor; RP uses ordinary trimming potentiometer, chip IC can be TWH8778-type electronic switch or TWH8752-type electronic switch. 👉 DIY and AdjustmentAfter the device is welded correctly, connect the mains power to the input end of the voltage regulator, cooperate with the voltage regulator and carefully adjust RP1, so that the relay J is closed when the voltage is 250V, and then the circuit is connected to the mains power grid. Ⅷ Temperature Fan Controller DiagramThis is an automatic fan temperature controlled governor, which can automatically adjust the speed according to the temperature change. The circuit can be adjusted, so it can be used for the control of other electrical equipment.👍 Circuit Working ModelFigure 8. Automatic Temperature Control and Speed Regulation in Fan CircuitThe IC in the picture is a 555 timer IC, which forms a multivibrator with components of R2, R3 and C2. It can send out a rectangular wave signal with an adjustable duty cycle. When the temperature changes, the resistance value of the thermistor changes, so the duty cycle of the square wave output by the multivibrator changes. Adjusting the conduction angle of the bidirectional thyristor VT changes the voltage across the fan electrodes, which automatically adjusts the speed of the electric fan. 👉 Components SelectionThe integrated circuit IC selects NE555 timer, and models such as LM555 and TLC555 can also be used. VT is a bidirectional thyristor, its withstand voltage should be above 400V, and the rated current should be reasonably selected according to the capacity of the electric fan to be controlled. Resistor R1～R5 can choose ordinary 1/8 or 1/4W carbon film resistors; Rt is a negative temperature coefficient thermistor, and can choose a thermistor with a resistance of about 10KΩ at room temperature. Capacitor C1 uses ordinary aluminum electrolytic capacitors; Capacitors C2 and C3 are polyester capacitors. VD is a Zener diode with a steady voltage of 9.1V. 👉 DIY and AdjustmentYou can make your own PCB, or use a universal one. After the circuit is installed, the temperature of the thermistor Rt can be artificially changed to observe the speed of the fan motor. If the temperature control effect is not ideal, the resistance value or temperature change range of the thermistor can be adjusted appropriately. Ⅸ Water Boiling Alarm Circuit DesignOnce the water boils in the kitchen, if it is not turned gas off in time, the boiling water will overflow and extinguish the flame. The gas may spill, which is very unsafe. This problem can be solved by using the water alarm.👍 Circuit Working ModelFigure 9. Boiling Water Alarm CircuitThis circuit uses thermistor as the temperature sensing element. When the water temperature rises, the resistance of the thermistor decreases and the potential at point A increases. When the potential at point A is higher than the conversion voltage of the IC-1 inverter, the IC -1 will output low level, IC-2 will output high level. Making the audio oscillator composed of IC-3 and IC-4 work, and the piezoelectric ceramic sheet makes sound. When IC-2 outputs low level, the audio oscillator doesn’t work, and the piezoelectric ceramic chip is silent. 👉 Components SelectionIC uses C066 two input terminal four NAND gate, working voltage 3V~18V, power supply is 3V~6V; RT thermistor selection resistance value is about 1kΩ; piezoelectric ceramic chip diameter is 27mm; resistor selection is ordinary 1/8 or 1/4W metal film resistors. 👉 DIY and AdjustmentFind two starter shells of waste fluorescent lamps, use iron sheet as a clip, close the tops of the two starters, and fasten them with screws. One of the starters can be set on the mouth of the kettle to obtain the temperature of the water. The two pins of the thermistor are welded on the cover of the other starter and put into the shell. Note that the thermistor must be close to the inner shell wall to facilitate heat transfer. Solder the outer lead of the thermistor and the temperature sensor. After all the components are welded and checked, you can turn on the power for debugging. Put the temperature sensor on the mouth of the kettle, and adjust the RP when the water boils to make the piezoelectric ceramic sheet sound. Repeat it several times before this circuit can be used normally. If you want to change the sound frequency, you can change the C2 capacity. If you feel that the sound is light, you can connect an external transistor to the IC-4 output terminal to amplify the sound.  Ⅹ FAQ1. How do you make a security alarm circuit?The cathode of the photodiode is connected to the supply while the anode is connected to a 10KΩ resistor. Another end of the resistor is connected to the ground. The anode terminal of the photodiode is also connected to pin 5 of the LM358 op-amp, which is the non-inverting terminal. 2. What is the technique of alarm circuits?In a closed-circuit system, the electric circuit is closed when the door is shut. This means that as long as the door is closed, electricity can flow from one end of the circuit to the other. But if somebody opens the door, the circuit is opened, and electricity can't flow. This triggers an alarm. 3. What is a security alarm circuit?This circuit will help you to guard your precious documents as well as jewelry from intruders or theft. All you need is just to place this circuit in front of the locker or below the mat so when any unknown person comes and walks over the switch, the circuit will trigger and the sound of an alarm comes. 4. What type of circuits are security alarms made of?The simplest type of contact-operated security circuit consists of an alarm bell (or a buzzer or electronic 'siren sound' generator, etc.), wired in series with a normally-open (n.o.) close-to-operate switch; the combination being wired across a suitable battery supply, as shown in the basic 'door-bell' alarm circuit ... 5. What are the three basic parts of an alarm system?The main components of an alarm system would be a sensor, a camera, a motion detector, a buzzer a flash light and batteries. It is a component that is usually used to detect noise or movement. Sensors are usually connected to the circuit. 

IntroductionOperational amplifier (op amp for short) is basically a voltage amplifying device designed to be used with components like capacitors and resistors, between its in/out terminals, or is simply a linear Integrated Circuit (IC) having multiple-terminals. In electronics, the open-loop voltage gain of the actual operational amplifier is very large, which can be seen a differential amplifier with infinite open loop gain, infinite input resistance and zero output resistance. In addition, it has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions. And meanwhile, it can be further simplified into an ideal op amp model, referred to as an ideal op amp (also called ideal OPAMP).CatalogIntroductionⅠ Ideal Op Amp Characteristics1.1 Infinite Input Resistance1.2 Zero Output Impedance1.3 Infinite Open-loop Gain1.4 Infinite Common-mode Rejection Ratio1.5 Infinite BandwidthⅡ Assumptions of Ideal Op AmpⅢ Working Characteristics of Ideal Operational Amplifiers3.1 Work in Linear Region3.2 Work in Nonlinear RegionⅣ Analysis of Ideal Operational Amplifier CharacteristicsⅤ Balanced Resistance Presets5.1 The Role of Balanced Resistance5.2 Input Balancing Resistor ExplanationⅥ Ideal Op Amp EquationsⅦ Several Common Op Amp CircuitsⅧ Difference Between Ideal Op-amp and Practical Op-ampⅠ Ideal Op Amp CharacteristicsWhen analyzing various application circuits of operational amplifiers, the integrated operational amplifier is often regarded as an ideal operational amplifier. The so-called ideal op amp is to idealize various technical indicators of op amps, and it must have the following characteristics.Characteristics of An Ideal Op-Amp1.1 Infinite Input ResistanceThe input terminal of an ideal operational amplifier does not have any current to flow in. In electronics, op amps are voltage gain devices. They amplify a voltage fed into the op amp and give out the same signal as output with a much larger gain. In order for an op amp to receive the voltage signal as its input, the voltage signal must be dropped across the op amp. If you know the concept of a voltage divider, voltage drops primarily across components with high impedances, proportionally according to ohm’s law by the formula V=IR. So the greater the resistance (or impedance) of a device, the greater the voltage drop across that device is. To make sure that the voltage signal drops fully on the op amp, it must have a very high input impedance, so that the voltage drops fully across it. If it had a low input impedance, the voltage may not drop across it and it would not receive the signal. This is why op amps must have high-input impedances.It’s also easy to make the input impedance lower (put a resistor in parallel) or the source impedance higher (put a resistor in series).Figure 1. Ideal Op Amp Symbol and Transfer Characteristic Curve 1.2 Zero Output ImpedanceThe output of an ideal op amp is a perfect voltage source, no matter how the current flowing to the amplifier load changes, the output voltage of the amplifier is always a certain value, that is, the output impedance is zero. In practice, zero output impedance is actually a distinct property from infinite input impedance, but for a very long time infinite input impedance was approached only with compromises in offset voltage and noise. 1.3 Infinite Open-loop GainIn an open-loop state, the differential signal at the input has an infinite voltage gain. This feature makes the operational amplifier very suitable for practical applications with upper negative feedback configuration. 1.4 Infinite Common-mode Rejection RatioAn ideal operational amplifier can only respond to the difference between the voltages at both ends of V+ and V-. In addition, the same part of the two input signals (ie common mode signal) will be completely ignored. What’s more, a high CMRR is required when a differential signal must be amplified in the presence of a possibly large common-mode input, such as strong electromagnetic interference (EMI). An example is audio transmission over balanced line in sound reinforcement or recording. 1.5 Infinite BandwidthThe ideal operational amplifier will amplify the input signal of any frequency with the same differential gain, which will not change with the change of signal frequency.Ⅱ Assumptions of Ideal Op AmpThe op amp can be considered a voltage controlled current source, or it is an integrated circuit that can amplify weak electric signals. Based on it, for an ideal OPAMP, what is the relationship between it and these electrical signals?First, assume that the current flowing into the input of the op amp is zero. This assumption is almost completely correct for FET op amps, because the input current for FET op amps is below 1pA. But for dual high-speed op amps, this assumption is not always correct, because the input current of it can sometimes reach tens of microamperes.Second, assume that the gain of the op amp is infinite, so the op amp can swing the output voltage to any value to meet the input requirements. It means that the output voltage of the op amp can reach any value. In fact, when the output voltage is close to the power supply voltage, the op amp will saturate. Maybe this hypothesis does exit, but needs a limit in practical. For example, at higher frequencies, the internal junction capacitors of transistor come into play, thus reducing the output and therefore the gain of amplifier. The capacitor reactance decreases with increase in frequency bypassing the majority of output. The opamp is in saturation state.Figure 2. Op Amp SaturationFor example, as per datasheet of LM741, large signal voltage gain is 200V/mv. It means an open loop gain of 200,000. If you operate an op-amp in open-loop condition(i.e. without negative feedback) ,even microvolts of input voltage (input offset voltage of LM741 is 3mv) will drive the output to saturation.In most of the amplifier circuits op-amp is configured to use negative feedback which greatly reduces the voltage gain (i.e. closed loop gain). In oscillators and schmit triggers, Op-amp is configured to use positive feedback. Comparator circuit is an example of the circuit which utilizes open-loop gain of op-amp. Its output will be always at saturation either positive or negative saturation. In an integrator circuit, the DC gain should be limited by adding a feed back resistor in parallel with capacitor ;else the output will get saturated .Even in amplifier circuits, the amplitude of the input signal and the voltage gain of the circuit should be balanced so that the output voltage does not exceed power supply voltage . For example for a non-inverting amplifier with a voltage gain of 100, the maximum permissible input voltage will be 150 mv if the VCC is 15 Volts. If you apply a signal of 200 mv ,the op-amp output will goto saturation as the required output will be 20 volts which exceeds the VCC of 15 Volts.Third, the assumption of infinite gain also means that the input signal must be zero. The gain of the op amp will drive the output voltage until the voltage (error voltage) between the two input terminals is zero. The voltage between the two input terminals is zero. The zero voltage between two input terminals means that if one input terminal is connected to a hard voltage source like ground, the other input terminal will also be at the same potential. In addition, since the current flowing into the input terminal is zero, the input impedance of the op amp is infinite.Fourth, of course, the output resistance of an ideal op amp is zero. An ideal op amp can drive any load without any voltage drop due to its output impedance. At low currents, the output impedance of most op amps is in the range of a few tenths an ohm, so this assumption is true in most cases. Ⅲ Working Characteristics of Ideal Operational Amplifiers3.1 Work in Linear RegionWhen the ideal op amp works in the linear region, the output and the input voltage show a linear relationship. Where u0 is the output voltage of the integrated op amp; u+ and u- are the voltages at the non-inverting input terminal and the inverting input terminal, respectively. Auo is the open loop differential voltage magnification. According to the characteristics of the ideal op amp, two important characteristics of the ideal op amp in the linear region.1) Zero differential input voltageSince the open-loop differential voltage magnification of an ideal op amp is equal to infinity, and the output voltage is a certain value, the voltage values at the non-inverting input terminal and the inverting input terminal are approximately equal. Just like short circuit between input and output, but it is fake. Because it is an equivalent short circuit, not a real short circuit, so this phenomenon is called "virtual short".2) Zero input currentSince the open-loop input resistance of an ideal op amp is infinite, no current flows into the op amp at either input. At this time, the current at the non-inverting input terminal and the inverting input terminal are both equal to zero. Like an disconnection, but an equivalent disconnection, so this phenomenon is called "virtual break". Virtual short and virtual break are two important concepts for analyzing the ideal op amp working in the linear region.In fact, the ideal operational amplifier has the characteristics of "virtual short" and "virtual break". These two characteristics are very useful for analyzing linear amplifier circuits. The necessary condition for virtual short is negative feedback. When negative feedback is introduced, at this time, if the forward terminal voltage is slightly higher than the reverse terminal voltage, the output terminal will output a high voltage equivalent to the power supply voltage after the amplification of the op amp. In fact, the op amp has a respond time changing from the original output state to the high-level state (the golden rule of analyzing analog circuits: the change of the signal is a continuous change process). Due to the feedback resistance of the reverse end change will inevitably affect its voltage, when the reverse end voltage infinitely close to the forward end voltage, the circuit reaches a balanced state. The output voltage does not change anymore, that is, the voltage at the forward end and the reverse end is always close. (Note: The analysis method is the same when the voltage decreases.) 3.2 Work in Nonlinear RegionWhen the op-amp operates in the nonlinear region, the output voltage no longer increases linearly with the input voltage, but saturates. The ideal op amp also has two important characteristics when operating in the nonlinear region.1) When u+ ≠ u-, the output voltage of the ideal op amp reaches the saturation value.When u+ > u-, the op-amp operates works in positive saturation region with a positive output voltage.When u+ < u-, the op-amp operates works in negative saturation region with a negative output voltage.Ideal op amp operates in the nonlinear region, u+ ≠ u-, there is no “virtual short”.2) The input current is equal to zero.Although the input voltage u+ ≠ u- above, the input current is considered to be zero. Ⅳ Analysis of Ideal Operational Amplifier CharacteristicsAs for Op-amp, there's probably a description like this: three-terminal element (circuit structure with double-ended input, single-ended output), ideal transistor, high-gain DC amplifier.(1) High input resistanceUnder this situation, the current flowing into the input terminal is close to 0, almost no signal source current is used, which is close to the voltage control characteristic. And virtual break is derived from this.(2) Lower output resistanceIt has the characteristics of adapting to any load. And the impedance of the subsequent load circuit will not affect the output voltage.(3) Infinite voltage amplification(4) Under a certain supply voltage condition, the amplifier can only work in closed-loop (negative feedback) mode, and the actual amplification is limited. Because op-amps themselves don't have a 0V connection but their design assumes the typical signals will be more towards the center of their positive and negative supplies. Thus, if your input voltage is right at one extreme or forces the output toward one supply, chances are it won't work properly. Working in open-loop mode is the like a comparator, and the output is high level orlow level.In the closed-loop (limited amplification) state, the amplifier is randomly compare the potentials of the two input terminals. The output stage makes immediate adjustments when they are not equal. So the final purpose of amplification is to make the potentials of the two input terminals equal. And virtual short is derived from this. Ⅴ Balanced Resistance Presets5.1 The Role of Balanced Resistance1) A suitable resistance is generally required to ensure that the input impedance is matched.2) In order to reduce the input current imbalance, the in-phase resistor should be equal to the parallel value of the two resistors at the reverse end in theory. In practice, as a result of the closed loop, especially in deep negative feedback conditions, the misalignment is not obvious at the output. And there is no need of in-phase grounding resistor when the misalignment is not the main problem. Because a balanced resistor is the starting point for an ideal op amp. In-phase grounding resistance is useful for bipolar op amps, and has no meanings for MOS-type op amps.3) Ground input termination resistance: it is necessary for impedance matching and high frequency setting.4) Bias current and offset current.For operational amplifiers with bias current greater than offset current, input resistance matching can be reduced, and precision circuits can compensate bias current to a minimum. If the bias current and offset current are similar, the matching resistance will increase the error.5) Set for the bias current at the input, the purpose of which is to equalize the impedance of the invertingand non-inverting inputs, so that two inputs with equal bias currents are assumed to have equal voltage drops, thereby counteraction can be made. 5.2 Input Balancing Resistor ExplanationA op-amp is connected to an inverting amplifier:Set the input resistance for R1, feedback resistance for Rfi,Assume that the non-inverting end is not connected to a balanced resistor, but grounded directly.Set the input bias current for the op-amp IB (same voltage in inverting and non-inverting end).The current flows through R1 and Rf are represented by I1 and If.Inverting voltage is V-, The op-amp gain is A.Use KCL in the inverting end (set the input signal to 0).Where (0-V-)/R1- (A+1)V- /Rf=IBFrom the above equation, it follows that V-=-(IB×R1×Rf/(Rf+(A+1)R1))At this time, the output voltage of the op-amp is Vo=A×(IB×R1×Rf/(Rf+(A+1)R1))The above formula can be approximated as Vo=IB×((A×R1)/Rf)If the in-phase terminal passes through a resistor R2 to ground and R2=R1/Rf, then the voltage at the in-phase terminal is V+=-IB×R2KCL is applied to the inverted terminal, where (0-V-)/R1+(A×(V+-V-)-V-)/Rf=IBAt this time the output voltage of the op-amp is Vo=0. Ⅵ Ideal Op Amp EquationsUnderstanding the basic conditions of an ideal op amp, and combining it with the Kirchhoff's current law (KCL) node voltage method and the superposition theorem of the node, is an effective method to analyze the ideal op amp circuit.As shown below, find the output voltage uoFigure 3. OPAMP Circuit1) Equation based on KCLFrom the concept of virtual break, i+=i-=0, then i1=i2, i3=i4, so (a)Based on virtual break, u+=u-, then (b)2) Node voltage methodList the node voltage equations for node 1 and node 2, and get (c)Note: Because the output current of the op amp is unknown at 1) and 2), it is not possible to list the KCL equation or node voltage equation at the output of the op amp. In addition, the op amp output uo in 2) should be treated as an independent voltage source. 3) Superposition theoremWhen there are multiple signal inputs, choosing the superposition theorem to solve can simplify the analysis and calculation process. The size of the output signal uo can be regarded as the superposition of the output signal obtained by the independent action of u1 and u2. When u1 acts alone, the u2 terminal is grounded, and the op amp output is: (d)Therefore, the final output of the operational amplifier is:   (e) Ⅶ Several Common Op Amp CircuitsNon-inverting Amplifier CircuitA non-inverting amplifier is an op-amp circuit configuration which produces an amplified output signal. It provides a high input impedance along with all the advantages gained from using an operational amplifier. Inverting Amplifier CircuitAn inverting amplifier (also known as an inverting operational amplifier or an inverting op-amp) is a type of operational amplifier circuit which produces an output which is out of phase with respect to its input by 180 degrees out of phase with respect to input signal. In the following figure, two external resistors to create feedback circuit and make a closed loop circuit across the amplifier. Op-amp as AdderAn adder circuit can be made by connecting more inputs to the inverting op amp. The circuit diagram of a summing amplifier is as shown in the following figure. Differential AmplifierDifferential amplifier is an analog circuit with two inputs and and one output in which the output is ideally proportional to the difference between the two voltages. It is a very useful op-amp circuit and by adding more resistors in parallel with the input resistors as shown in the following. Composite AmplifierThe composite amplifier is termed as a combination of multiple operational amplifiers that are cascaded together with a negative-feedback loop around the entire network. The resistance in the circuit is generally selected at the K ohm level, the ratio of the resistance affects the gain and bias, in addition, the supply current, frequency response and capacitive load driving capability of the op amp determine their specific values in circuits. If it is used in a high-frequency circuit, the resistance needs to be reduced to obtain a better high-frequency response, but it will increase the input bias current, thereby increasing the current of the power supply. Ⅷ Difference Between Ideal Op-amp and Practical Op-ampIdeal op amps use no power, have infinite input impedance, unlimited gain-bandwidth and slew rate, no input bias current, and no input offset. They have unlimited voltage compliance.Practical op amps consume some power, have very high input impedance have limited gain-bandwidth and limited slew rate, have some input bias current and input offset voltage. Voltage compliance is limited by the power supply rail, or frequently even less.Still practical op amps are very useful because most of the limitations listed above are way better than what your circuit needs.For an ideal amplifier, it does not draw any current at all from its input. Assuming a two input amplifier the signal current in both input probes is zero. In other words the input impedance must be infinite. The output, should operate as the output of an ideal voltage source. This means that the potential between the output and the ground must be A(v2−v1), no matter how much current would a load connected to the output would draw. In other words the output impedance must be zero.For a real amplifier, the input impedance must be as large as possible while the output impedance must be as low as possible.In fact, An op-amp in real life, however, cannot operate with zero current flow. Frequently Asked Questions about Ideal Op Amp1. What is characteristic of ideal opamp?Ideal op amps will have infinite voltage gain, infinitely high impedance, zero output impedance, its gain is independent of input frequency, it has zero voltage offset, its output can swing positive or negative to the same voltages as the supply rails, and its output swings instantly to the correct value. 2. How does an ideal op amp work?An operational amplifier, or op amp, generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance (no greater than 100 Ω). ... Open-loop voltage gain runs very high, on the order of 1 million. 3. Why are op amps not ideal?Op-amps with FET inputs have an Ibias that is so small that this method becomes less practical. Instead of measuring the voltage drop across a resistor, one can monitor the change in voltage across a capacitor as it is charged by the bias current. 4. How are real op amps different from ideal op amps?In real op amps, the amplified signal will not fully reach the DC supply rails. They will fall short of it. In an ideal op amp, the output will swing instantly to the amplified voltage value. There will be no time delay between the time the voltage is input into the op amp till the time it is output. 5. What are the four main ideal characteristics of an open-loop op amp?An ideal op amp is usually considered to have the following characteristics:Infinite open-loop gain G = vout / vInfinite input impedance Rin, and so zero input currentZero input offset voltageInfinite output voltage rangeInfinite bandwidth with zero phase shift and infinite slew rateZero output impedance R

Executive Summary: Proximity Sensors in 2026What is a proximity sensor? A non-contact device that detects the presence or distance of an object using electromagnetic fields, light, or sound waves. Essential for Industry 4.0 automation, robotics, and consumer electronics.Key Types: Inductive (Metals), Capacitive (Non-metals/Liquids), Ultrasonic (Distance/Clear objects), Photoelectric (Long-range), and IR (Short-range).2026 Trends: Integration with IO-Link for predictive maintenance, miniaturized MEMS technology, and AI-driven signal processing for higher accuracy in harsh environments.Ⅰ What is a Proximity Sensor? (2026 Overview)A proximity sensor is a non-contact electronic instrument that detects the presence, proximity, or exact distance of an object without physical contact. In the 2026 landscape of industrial automation, these sensors serve as the "eyes" of machines, ensuring precise control in manufacturing, robotics, and smart devices.While there are many types of proximity sensors, they share a common operational principle: they transmit an electromagnetic field, electrostatic field, or beam of light, and analyze the reflection or field disruption to confirm if an object (the target) is approaching, leaving, or present. The maximum detection limit is defined as the "rated range." Modern smart sensors allow this range to be dynamically adjusted via software protocols like IO-Link. Proximity sensors are renowned for high reliability and zero mechanical wear, as the lack of physical contact prevents component fatigue, giving them a functional lifespan often exceeding 100,000 hours in industrial settings. The five primary categories utilized in 2026 include:Inductive: For ferrous and non-ferrous metals.Capacitive: For liquids, plastics, and powders through barriers.Ultrasonic: For sound-based distance measurement.Photoelectric: For long-range light detection.Hall Effect: For magnetic field detection. Ⅱ How Does a Proximity Sensor Function?Proximity sensors work by emitting a specific field or signal (electromagnetic, electrostatic, or acoustic) and measuring changes in the return signal caused by a target object.2.1 Inductive Sensor PrincipleInductive sensors generate an electromagnetic field via an internal oscillator. When a conductive metal object enters this field, eddy currents are induced in the target, causing a dampening of the oscillation amplitude. The sensor detects this energy loss to trigger a switch.2.2 Capacitive Sensor PrincipleCapacitive sensors function as an open capacitor. They generate an electrostatic field between the sensing electrode and the ground. When any object (metal, water, plastic) enters this field, the capacitance increases, changing the oscillation frequency. Once this frequency crosses a DC voltage threshold, the sensor activates. Ⅲ Detailed Types of Proximity SensorsChoosing the right sensor depends on the target material and environment. Below is the breakdown of the industry standards for 2026.3.1 Inductive Proximity Sensor (Metal Detection)Best for: Harsh industrial environments, detecting machine parts, gears, and cams. Inductive sensors remain the backbone of heavy industry. They utilize a coil-wound oscillator to create a high-frequency magnetic field. They are robust, impervious to oil, dirt, and water (often rated IP67/IP69K), and rely on the principle of induction (Faraday's Law).  Key Characteristics:Target: Metals only (Iron, Steel, Aluminum, Copper).Range: Short (typically 1mm to 60mm).Speed: High switching frequency (up to 5 kHz), ideal for counting rotating gears.Ferrous vs. Non-Ferrous: Detection distance is greatest for ferrous metals (iron) and reduced for non-magnetic metals (aluminum) unless "Factor 1" sensors are used. 3.2 Capacitive Proximity Sensor (Versatile Detection)Best for: Level detection through container walls, detecting plastics, liquids, and granulars. Unlike inductive sensors, capacitive units detect changes in dielectric constant, allowing them to sense virtually any material. They contain two charging plates (internal and external/sensing face). When a target approaches, it alters the dielectric capacity, triggering the switch. Pros & Cons:See-Through Ability: Can detect water inside a plastic tank or powder inside a glass tube.Speed: Slower than inductive (10 to 50 Hz).Sensitivity: Can be adjusted to ignore thin container walls while detecting the contents. 3.3 Ultrasonic Proximity Sensor (Sound Waves)  Best for: Transparent objects (glass, clear plastic), long distances, and difficult lighting conditions. Ultrasonic sensors utilize echolocation—similar to bats or dolphins. A piezoelectric transducer emits a high-frequency sound pulse (chirp) and measures the "Time of Flight" (ToF) for the echo to return. Advantages in 2026:Color Immunity: Unlike optical sensors, color or transparency does not affect accuracy.Distance: Capable of detecting objects several meters away.Blind Spots: While effective, they have a "dead zone" immediately in front of the sensor face.  Limitations: Performance can be impacted by air turbulence, foam on liquids, or extreme temperature fluctuations (which alter the speed of sound), though modern units include temperature compensation. 3.4 IR Proximity Sensor (Infrared) Best for: Short-range detection, security systems, and mobile devices. IR sensors emit a beam of infrared light. If an object is present, the light reflects back to a photodetector at a specific angle (triangulation). These are cost-effective but can be confused by ambient sunlight or dark surfaces that absorb light rather than reflect it. 3.5 Photoelectric Sensor (Optical)Best for: Long-range detection, packaging lines, and logistics.  Photoelectric sensors use a light transmitter (LED or Laser) and a receiver. They are modulated to specific frequencies to avoid interference from ambient light.  Three Key Configurations:Through-Beam: Emitter and receiver are separate. Detects when the beam is broken. Longest range (up to 50m+).Retroreflective: Emitter and receiver in one unit; requires a reflector. Medium range.Diffuse: Light reflects off the object itself. Short range, but easy to install. Ⅳ Key Applications in Industry 4.0  By 2026, proximity sensors are integral to the Industrial Internet of Things (IIoT):Automotive & EV Manufacturing: Inductive sensors detect chassis positioning and gear rotation speeds with extreme precision.Food & Beverage: Capacitive sensors monitor liquid levels in bottles and grain levels in silos through sight glass.Logistics & Warehousing: Photoelectric sensors trigger conveyor belts and size parcels for automated sorting.Smart Electronics: Mobile phones use proximity sensors (often IR or Time-of-Flight/LiDAR) to disable touchscreens during calls or for facial recognition.Vibration Monitoring: Analog proximity sensors measure shaft runout and vibration in large turbines to predict maintenance needs.  Ⅴ Buyer's Guide: How to Choose a Proximity SensorSelecting the correct sensor requires analyzing the target material, environmental constraints, and required range. Use this 2026 decision matrix: Selection CriteriaKey ConsiderationsRecommended Sensor TechnologyTarget Material• Is the object Metal?• Is it Non-Metal (Plastic, Liquid, Wood)?• Is it Transparent (Glass, Clear Film)?• Metal: Inductive (Best reliability)• Non-Metal/Liquids: Capacitive• Transparent: UltrasonicEnvironment• Is it dirty, oily, or dusty?• Are there extreme temperatures?• Is washdown required (IP69K)?• Dirty/Oily: Inductive or Capacitive (Excellent immunity)• Clean/Dry: Photoelectric or IR• Avoid in Dust/Smoke: Optical sensorsSensing Range• Very Close (<50mm)• Medium Range (50mm - 2m)• Long Range (>2m)• Close: Inductive / Capacitive• Medium: Diffuse Photoelectric / Ultrasonic• Long: Through-beam Photoelectric / LiDAR  Ⅵ Frequently Asked Questions (FAQ)1. What does a proximity sensor do in simple terms?It detects if an object is nearby without touching it. This triggers an action, like stopping a machine for safety, counting items on a conveyor, or turning off your phone screen when you hold it to your ear. 2. Which sensor detects plastic or water?Capacitive proximity sensors are the industry standard for detecting non-metallic objects like plastic, glass, wood, and liquids (water, oil, chemicals). 3. Can inductive sensors detect aluminum?Yes, but with reduced range compared to ferrous metals like iron or steel. However, modern "Factor 1" inductive sensors can detect aluminum and steel at the same distance. 4. What is the typical range of a proximity sensor?Inductive and Capacitive sensors typically work between 1mm and 60mm. Ultrasonic sensors can measure up to several meters, and Photoelectric sensors can reach 50+ meters in through-beam configurations. 5. Are ultrasonic sensors affected by color?No. Since they use sound waves, ultrasonic sensors are color-blind. They are ideal for detecting clear glass, black plastic, or highly reflective surfaces that confuse optical sensors. 6. What is the difference between NPN and PNP sensors?This refers to the output transistor type. PNP sensors switch the positive voltage to the output (common in Europe/USA), while NPN switches the negative/ground (common in Asia). 7. How accurate are modern proximity sensors?High-end inductive sensors in 2026 offer repeatability down to 0.001mm (1 micron), making them suitable for precision CNC machining and quality control.{ "@context": "https://schema.org", "@type": "Article", "headline": "Proximity Sensors Explained: Types, Principles, and Applications (2026 Guide)", "datePublished": "2021-04-14", "dateModified": "2026-01-07", "description": "A comprehensive guide to proximity sensors in 2026. Learn about Inductive, Capacitive, Ultrasonic, and Photoelectric sensors, their working principles, and how to choose the right one for industrial automation.", "articleBody": "What is a Proximity Sensor? A proximity sensor is a non-contact electronic instrument that detects the presence, proximity, or exact distance of an object without physical contact...", "mainEntity": { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What does a proximity sensor do?", "acceptedAnswer": { "@type": "Answer", "text": "A proximity sensor detects the presence or absence of an object without physical contact. It emits an electromagnetic field, light, or sound and measures the reflection or disruption to trigger a signal. Common uses include industrial automation, safety systems, and mobile phone screen control." } }, { "@type": "Question", "name": "How do I choose between inductive and capacitive sensors?", "acceptedAnswer": { "@type": "Answer", "text": "Choose an **Inductive Sensor** if you need to detect **metal** targets in dirty environments (oil/dust). Choose a **Capacitive Sensor** if you need to detect **non-metallic** objects like plastic, wood, or liquids, or if you need to see through a non-metallic container wall." } }, { "@type": "Question", "name": "What are the limitations of ultrasonic sensors?", "acceptedAnswer": { "@type": "Answer", "text": "Ultrasonic sensors can be affected by extreme air temperature changes (affecting the speed of sound), air turbulence, and soft sound-absorbing materials (like foam or cloth). 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CatalogⅠ Isolation Transformer DefinitionⅡ Isolation Transformer ConstructionⅢ How Isolation Transformers Work?Ⅳ What's the Main Function of an Isolation Transformer?Ⅴ Special Purpose Isolation Transformers 5.1 Pulse Transformers 5.2 Austin Transformers 5.3 Instrument TransformersⅥ What are the Benefits of Isolation Transformers?Ⅶ Isolation Transformers VS AutotransformersⅧ FAQⅠ Isolation Transformer DefinitionTwo copper coils that are wrapped around each other and are each supplied by their own power source make up an isolation transformer. While the term "isolation transformer" applies technically to any transformer, it is specifically a transformer that isolates an alternating current from a circuit. By separating two circuits with an induction loop or lowering the voltage of the alternating current until it enters the circuit itself, an isolation transformer does this. Transformers isolated from each other with main (input) and secondary (output) windings are known as isolation transformers. Under this configuration, a dielectric insulation barrier electrically separates the input power and output power.Ⅱ Isolation Transformer ConstructionTransformers can be described as two coils surrounding a core of ferromagnetic material, as shown in Figure 4.The main and secondary coils are shown in the schematic representation; the electric source is connected to the primary, and the isolated output is taken from the secondary. Physically, the coils are distinct from each other and the heart. An early transformer was first used by Michael Faraday during his studies studying electromagnetism. Faraday found that a current-carrying wire generates a magnetic field surrounding the wire and that a current in one generated a magnetic field when two different wires were coiled around a toroid of soft iron, and the changing flux, in turn, induced a voltage in the other. Now known as mutual induction, Faraday is credited with finding that a shifting magnetic flux is caused in a circuit by an electromotive force according to the formula:Sometimes this is shown using the absolute value of E:  The negative indicating the electromotive force opposes the current.Although isolation is provided by any transformer consisting of two separate coils and no grounding shields, the term isolation transformer applies to transformers specifically designed for electrical insulation, the primary purpose of which is to isolate the AC source from circuits, devices and primary and secondary windings. They also have special insulation between the primary and secondary coils and are built between windings to withstand high voltages. Since the capacitance and resistive paths of the coils can be connected to power line/transient voltage noise, isolation transformers have additional features to minimize common-mode noise (which occurs on both hot and neutral ground-referenced wires), transverse mode noise (which occurs between hot and neutral wires) and electromagnetic noise. DC signals and interference caused by ground loops are blocked by the transformer. To reduce any capacitance between the windings, electrostatic shields are used for sensitive equipment (computers or measuring instruments). The insulation transformers used for protection generally have a 1:1 turn ratio, with the number equal to the turns in the primary and secondary windings, but when the voltage still needs to be changed, step-up and step-down isolation transformers are used. Check the specifications for the included features, the scores, and how they are designed when selecting an isolation transformer.Ⅲ How Isolation Transformers Work?Isolation transformers act in the same manner as other transformer types. To allow the primary coil to induce a current in the secondary coil, the isolation transformer is made of two electromagnets that are wrapped around each other. If more than the secondary coil is wound in the primary coil, the voltage is diminished. If more than the primary coil is wound into the secondary coil, the voltage is increased. In order to maintain the same voltage but to distinguish two circuits, an isolation transformer could have primary and secondary coils that are wound the same by causing a current from one coil to the other rather than providing a direct link.Ⅳ What's the Main Function of an Isolation Transformer?Its main role is to include certain circuits that are not capable of directly handling an alternating current safely. Not only does this ensure the full protection of your system, but it also helps to prevent short-circuits or fire accidents. It is included in most of the equipment to reduce the voltage until it hits the application for safety purposes. Another essential feature of using this transformer is that it helps to manage any required amount of voltage.Ⅴ Special Purpose Isolation TransformersIsolation transformers have been developed for specialized applications. Some examples are:5.1 Pulse Transformers: Optimized for the propagation of rectangular electrical pulses and to provide digital signal electrical isolation. These are used in the networking of computers.5.2 Austin Transformers: These power the air-traffic obstacle lamps you see on antenna structures, invented by Arthur O. Austin. The lighting circuitry on the antenna mast would conduct radio-frequency energy to the earth, if not isolated. The AC building mains are also completely separated from the tower by these transformers.5.3 Instrument Transformers: They are used to provide reliable voltage for meters and to securely isolate control circuits from high voltages/current. The transformer's primary winding is linked to the high voltage/current circuit and the meter, much like the connections shown in Figure 3, is linked to the secondary circuit.Note: Some transformers are manufactured with only one winding that is tapped on the winding at various locations to split it into main and secondary portions. Known as auto-transformers, as the single winding is shared, these devices do not provide isolation. Separate coils have isolation transformers, with no physical connection between the coils, no ground on earth.Ⅵ What are the Benefits of Isolation Transformers?Because of their diverse uses and advantages, different industries and companies use isolation transformers. Some of its most significant advantages are listed here.• Isolation can be replaced by isolation transformers in various circuits. With a 1:1 ratio, the main and secondary windings can be separated by insulation transformers.• Transformers of isolation allow direct current power isolation simpler. In the case of telephone lines, where amplifiers are needed at different intervals, the separation of direct current components from the signal is performed by isolation transformers to control every amplifier on the line.• By uniting a vessel with the electric power source, isolation transformers eliminate the possibility of electric shock. They allow the isolation of the person from the resource in such a way that the electrical wires do not directly contact the power line.• Without isolation in electronics testing and servicing, it can prove dangerous to contact a live portion of the circuit. For isolation, 1:1 ratio transformers are therefore used to provide protection. For gadgets that use electricity, isolation transformers have therefore proven to be an excellent choice.• With the aid of isolation transformers, all kinds of noise and sound produced by connecting the signal from the audio amplifier to the speaker output circuit are minimized.• The amount created by a radio frequency on wide circuit devices is separated from the transmitter line by isolation transformers. They facilitate the relation to the transmitted signals of the amount generated by the radio frequency amplifier and direct it toward the antenna.Ⅶ Isolation Transformer VS AutotransformerAn isolation transformer is a main and secondary coil winding electrical transformer. By insulation, these windings are isolated. This insulation reduces the possibility of electrocution by simultaneously contacting the active components and the ground.An autotransformer is a single-winding electrical transformer. The term "auto" applies not to any kind of automatic system but single-coil working alone. Portions of the same winding serve as both the main and secondary sides of the transformer in an autotransformer.• Operation of an Isolation TransformerAn isolation transformer's primary function is to separate circuits. These transformers are designed and produced between the two windings with attention to capacitive coupling. Alternating current (AC) current from the primary to the secondary will also be coupled by the capacitance between primary and secondary windings.• Operation of an AutotransformerAn autotransformer's primary function is to control the transmission line voltage and can be used to convert voltages. An autotransformer automatically changes the voltage according to the load, with only one winding. Such transformers require the correct operation of AC currents and will not operate on direct current.• Common Applications for an AutotransformerBoost at end of the long transmission line to compensate for line lossesReduced starter voltage for an induction motorTo enable rectifier output control, multi-tap feeding the primaryFluorescent light fixture start-up• Common Applications for an Isolation TransformerComputers and peripheralsMedical EquipmentRemote control equipmentTelecommunication equipment Ⅷ FAQ1. What is an isolation transformer?Isolation transformer is basically a transformer with winding ratio of 1:1, i.e., it has same number of primary as well as secondary windings.Isolation transformer provides electrical isolation between two circuits by transfering energy in magnetic form from one circuit to another.First circuit is connected in primary of transformer. Electric supply on this circuit is converted to magnetic field on primary winding and magnetic field magnetises secondary winding which is converted into electrical energy again in secondary circuit. Since it has 1:1 winding ratio voltage and current level of secondary circuit are same as that of primary circuit. So both circuits are electrically isolated yet energy is being transferred between them. 2. Where and why are isolation transformers used?As the name suggests, they are used to isolate the two circuits electrically by providing a galvanic isolation between them. There are many reasons to use an isolation transformer.Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass.Isolation transformers are used for impedance matching to get the most efficient power transfer between stages and to keep different stages electrically isolated to prevent ground loops.Isolation transformers prevents harmonics from transferring from one side to other side. 3. How does an isolation transformer protect against an electric shock?It doesn’t always protect against an electric shock but it will protect against an electric shock to earth for a single fault in a Multiply Earthed Neutral (MEN) system. Current needs a return path to the source and if teh secondary windings of the isolating transformer are not earthed then there is no return path for current flowing through the person back to the other terminal of the secondary winding. All that happens is that the contacted winding assumes the earth potential.You will still get shocked if you contact both terminals or if you have multiple devices with earth faults that provide a return path for the current.The benefit is that the isolating transformer continues to supply current even in the event of a short to earth on one of its secondary windings. 4. What are the disadvantages of isolation transformer?The Isolation Transformer is a specially designed transformer which is used to isolate two different electrical circuits. The Isolation Transformer is mainly used to isolate the load or powered device from the power supply.Some Disadvantages of Isolation Transformer are given below.• When the Isolation Transformer operating as Pulse Transformer and it operate at low frequency there is distortion produces in secondary or output waveform.• When isolation transformer operating at DC pulse signal, the saturation property of the core reduces.• Isolation Transformer specially designed, that is why it is costlier than a normal transformer. 5. What's the difference between an isolation transformer and a regular transformer?• The transformers having primary and secondary winding which are separated from each other known as Isolation transformer where as Regular Transformer are used for sending and receiving electricity .• Isolation transformers are not used to increase or decrease voltage and Regular Transformer is used to increase or decrease the voltage and current in an electrical circuit.• There are used to breaking the circuit into primary and secondary, so direct current noise can’t get through. Regular Transformers are designed to modify an alternating current voltage that runs from one electric circuit to another through electromagnetic induction. 6. What is the difference between isolation transformer and step up transformer?Main purpose of isolation transformer is to electrically isolate two sides or circuits. This is done mostly for safety reasons. You may make the second side shock proof, or it may have its own DC supply.Usually the turns ratio of isolation transformer is one, meaning input and output will be same in magnitude, though occasionally it could be different.While primary of transformer may be connected to live wire, secondary becomes safe from electric shock. Two different circuits can be connected this way.Step up transformer is used for increasing the voltage from one level to a higher one. Main purpose is to have higher voltage level for the circuit on secondary side. The two sides may or may not be isolated, and turns ratio is greater than one. 7. What is the working principle of an isolating transformer?Isolation transformer is just similar to our normal transformer but the difference is in the transformation ratio. It is 1:1 in isolation transformer. So it also works on the Faraday's law of mutual induction. It says that the emf induced in the secondary coil due to te production of magnetic flux by the voltages and currents of the primary coil. 8. What are the applications of isolating transformers?• The main application of Isolation Transformer is, to make the isolation between a power supply and a powered circuit or powered device for the safety purpose.• Isolation Transformer is used to transform electrical power between two circuits which are not connected electrically to each other. Those two circuits are may have the same voltage level or different voltage level.• Isolation transformers are can be used as Pulse Transformer.• Isolation transformers are used for computer network design. Here isolation transformer act as Pulse Transformer.• Sometimes the Isolation Transformer used in electrical circuits as well as an electronic circuit to provide protection against Electrical shock. 9. Why do we need an isolation transformer to connect an oscilloscope?The scope input shield is connected to the power outlet ground via the scope chassis for safety. It should never be connected to any point not at the same potential as that ground.Either the device under test should also be grounded, or completely isolated from ground. The isolation transformer is the preferred method in most cases.When testing circuits solely using DC power, a lab type DC supply may have outputs isolated from ground. This is also acceptable.It is important to think of all possible paths that arise through connections to other equipment, or parts of a system. The isolation transformer is safe in the most situations.  10. What is the working process of an isolation transformer?Isolation transformers are very important for providing isolation in medical instruments powered by the mains grid (220 V or 110 V AC), which is connected to the primary of an isolation transformer, but where the electronic network connected to the patient is connected to the secondary of the transformer. Since the secondary network is isolated from the primary, there is no path for an AC current from the mains to go to the ground through the patient.