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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. 

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. 

CatalogCatalogⅠ Oscillation DefinitionⅡ Definition of Voltage Controlled OscillatorⅢ Types of Voltage Controlled Oscillator  3.1 Harmonic Oscillators  3.2 Relaxation OscillatorsⅣ Working Principle of Voltage Controlled OscillatorⅤ Voltage Controlled Oscillator Requirements  5.1 VCO tuning range  5.2 VCO tuning gain  5.3 VCO V/f slopeⅥ Voltage Controlled Oscillator FeedbackⅦ Colpitts & Clapp Voltage Controlled Oscillator CircuitsⅧ Voltage Controlled Oscillator Varactor Issues  8.1 Abrupt  8.2 Hyper-abruptⅨ FAQⅠ Oscillation DefinitionAn oscillator is a circuit that, without any input, generates a continuous, repeated, alternating waveform. Basically, oscillators transform unidirectional current flow from a DC source into an alternating waveform that, as determined by its circuit components, is of the desired frequency. By observing the behavior of the LC tank circuit shown in Figure 1 below, which uses an inductor L and a completely pre-charged capacitor C as its components, the basic theory behind the operation of oscillators can be understood. In this case, the capacitor initially begins discharging through the inductor, which results in the conversion of its electrical energy into an electromagnetic field that can be stored in the inductor. There will be no current flow in the circuit until the capacitor discharges fully.The stored electromagnetic field, however, would have created a back-emf by then, which results in the flow of current through the circuit in the same direction as before. This flow of current through the circuit continues until the electromagnetic field collapses, resulting in the electromagnetic energy back-conversion into electrical form, allowing the cycle to repeat. Now, however, the capacitor would have been charged with the opposite polarity, because of which an oscillating waveform is obtained as the output. However, because of the resistance of the circuit, the oscillations that occur due to the inter-conversion between the two energy-forms will not continue indefinitely as they will be subject to the impact of energy loss. The amplitude of these oscillations gradually decreases to zero as a result, making them damp. This means that the energy loss needs to be balanced to achieve continuous oscillations and constant amplitude. However, in order to achieve oscillations of constant amplitude, it should be noted that the energy supplied should be precisely regulated and must be equal to that of the energy lost.Ⅱ Definition of Voltage Controlled OscillatorA voltage-controlled oscillator (VCO) is an output signal oscillator whose output can be varied over a particular frequency range that is controlled by the DC voltage input. It is an oscillator whose output frequency is directly connected by its input to the voltage applied (FM control).A main parameter of the VCO is the sweeping time: this is the minimum time required to turn or sweep from minimum frequency to maximum frequency or reverse. From an external analog signal, the VCO can be modulated by amplitude (AM). To produce the requested RF power level, an external power amplifier may be required.Ⅲ Types of Voltage Controlled OscillatorThe VCOs can be categorized based on the output waveform:• Harmonic Oscillators• Relaxation Oscillators3.1 Harmonic OscillatorsThe output waveform that harmonic oscillators generate is sinusoidal. This can also apply to the oscillator that regulates the linear voltage. The LC and Crystal oscillators are examples. Here, the capacitance of the diode varies according to the voltage around the diode. This in turn alters the LC circuit's capacitance. Hence, the frequency of the output will change. The advantages are frequency stability in terms of power supply, noise and temperature, and frequency control precision. The only downside is that this form of the oscillator on monolithic ICs can not be implemented effortlessly.3.2 Relaxation OscillatorsThe waveform output produced by harmonic oscillators is a screwed tooth. Using the decreased amount of components, this type may provide a wide range of frequency. It can primarily be used in ICs that are monolithic. The oscillators for relaxation may have the following topologies: • Delay-based ring VCOs • Grounded capacitor VCOs • Emitter-coupled VCOs Here: In delay-based ring VCOs, in a ring shape, the gain stages are connected. As the name implies, in every single point, the frequency is connected to the delay. The VCOs of the second and third types act almost equally. The time taken in each stage is directly linked to the capacitor's charging and discharging time.Ⅳ Working Principle of Voltage Controlled Oscillator Using several voltage regulation electronic components such as varactor diodes, transistors, Op-amps, etc., VCO circuits can be built Here, using Op-amps, we are going to address the function of a VCO. Below, the circuit diagram is shown.A square wave is going to be the output waveform of this VCO. The output frequency is, as we know, connected to the control voltage. The first Op-amp will act as an integrator inside this circuit. The arrangement of the voltage divider is applied here. Because of this, half of the control voltage given as input is supplied to the Op-amp 1 positive terminal. At the negative terminal, the same voltage level is retained. This is to maintain the voltage drop, R1 as half of the control voltage, across the resistor. The current flowing from the R1 resistor passes through the MOSFET when the MOSFET is in good condition. The R2 has half of the resistance, the same drop in voltage and twice the current as of the R1's. So, the attached capacitor is charged by the extra current. To supply this current, the Op-amp 1 should have a gradually increasing output voltage. The current flowing from the R1 resistor passes through the capacitor and gets discharged when the MOSFET is out of order. The output voltage obtained at this time from the Op-amp 1 will decrease. A triangular waveform is therefore produced as the output of Op-amp 1. The Op-amp 2 will act as a catalyst for Schmitt. A triangular wave that is the output of the Op-amp 1 is the input to this Op-amp. If the input voltage is greater than the threshold level, VCC will be the output from the Op-amp 2. If the input voltage is lower than the threshold level, the Op-amp 2 output is zero. The output of the Op-amp 2 is therefore going to be square waves. LM566 IC or IC 566 is an instance of VCO. In fact, it is an integrated 8-pin circuit that can generate double-square wave and triangular wave outputs. Below, the internal circuit is depicted.Ⅴ Voltage Controlled Oscillator RequirementsThere are several parameters that must be considered before the design begins when designing a voltage-regulated oscillator, VCO. These describe the parameters of key performance required for the VCO. 5.1 VCO tuning rangeIt is clear that the oscillator that is powered by voltage must be able to tune over the range that the loop is supposed to work over. This requirement is not always simple to satisfy and, in certain extreme situations, can require the VCO or resonant circuit to be switched. 5.2 VCO tuning gainThe gain of the oscillator regulated by voltage is important. It is calculated per Hz (or V/MHz, etc) in terms of volts. It is the tuning shift for a given change in voltage, as indicated by the units. Any of the overall loop design factors and measurements are influenced by the voltage-controlled oscillator gain.At lower frequencies, the VCO response curves can be shown to be relatively straight. They typically flatten out at higher voltages, however, where the capacitance changes from the variable diodes decrease. 5.3 VCO V/f slopeFor any voltage-driven oscillator used in a phase-locked loop, it is a crucial requirement that the voltage to frequency curve is monotonic, i.e. it always shifts in the same context, usually increasing voltage frequency. If ti alters, as can generally occur in some instances due to spurious resonances, etc., this can cause the loop to become unstable. This must therefore be avoided if the phase-locked loop is to work satisfactorily. This curve shows a slight dip which will result in an unstable phase-locked loop.Phase noise efficiency: In some PLL applications, the phase noise performance of the voltage regulated oscillator is of particular importance - particularly where it is used in frequency synthesizers. Outside of the PLL loop bandwidth, the phase noise output of the voltage-regulated oscillator is the dominant factor in phase noise. While the operation of the PLL reduces close-in noise, there is no reduction in VCO phase noise outside the loop bandwidth. These are some of the main specifications that must be understood from the outset of the VCO design. Careful optimization of the tuned circuit Q, especially the use of variable diodes with as high a Q as possible, selection of the active system, optimization of the oscillator feedback.Ⅵ Voltage Controlled Oscillator FeedbackA VCO can be considered, like any oscillator, as an amplifier and a feedback loop. It is possible to denote the amplifier's gain as A and the feedback as B. For the circuit to oscillate, 360 ° must be the complete phase shift around the loop and unity must be the gain. Signals are fed back around the loop in this manner so that they are addictive and, as a result, any slight disturbance in the loop is fed back and builds up. Because the feedback network is frequency-dependent, the signal is based on one frequency, the feedback network is resonant, and a single frequency signal is produced. A typical emitter circuit is used by many oscillators and thus by VCOs. This in itself generates a 180° phase shift, leaving a further 180° to be given by the feedback network. A typical base circuit where there is no phase shift between the emitter and collector signals (assuming a bipolar transistor is used) can be used by other oscillator or VCO circuits and the phase shift network must provide either 0 ° or 360 °. The device requires a resonant circuit for the oscillator to oscillate on a given frequency to ensure that the oscillation happens on a given frequency. The resonant circuit may be one of a variety of LC resonant circuit configurations, depending on the circuit, or a quartz crystal, etc., in either series or parallel resonance.Ⅶ Colpitts & Clapp Voltage Controlled Oscillator CircuitsThe Colpitts and Clapp oscillator circuits are two commonly used formats for the VCO. Of the two, the most commonly used is the Colpitts circuit, but both are somewhat similar in their configuration. These circuits serve as oscillators because an active device such as a bipolar transistor with capacitors positioned between the base and the emitter (C1) and the emitter and the ground (C2) has been found to fulfill the requirements needed to provide adequate feedback for the output of the oscillator in the correct step. The C1:C2 ratio must be greater than one for the oscillation to take place. The resonant circuit is rendered between the base and ground by adding an inductive function. This consists of only an inductor in the Colpitts circuit, while an inductor and capacitor in series are used in the Clapp circuit.The resonance conditions are that:The capacitance for the overall resonant circuit consists of a series of combinations of the two C1 and C2 series capacitors. The capacitor in the series with the inductor is also used in the series with C1 and C2 in the case of the Clapp oscillator.The capacitance of the series is thus:It is important to change the resonant point of the circuit to make the oscillator tune. This is better accomplished in the case of the Colpitts oscillator, by inserting a capacitor across the indicator. Alternatively, the capacitor may be in series with the inductor for the Clapp oscillator. A circuit where the inductive reactance is located between the base and ground is often favored for high-frequency applications because it is less vulnerable to spurious oscillations and other anomalies.Ⅷ Voltage Controlled Oscillator Varactor IssuesIn order to ensure that the drive frequency in the tuned circuit is not too high, caution must be taken in the design of the circuit when varactor diodes are used inside a voltage-driven oscillator. If this is the case, then the varactor diodes, reducing the Q and increasing the number of spurious signals, can be forced into forwarding conduction. Within a VCO, there are two main types of varactor diode that can be used-the name refers to the diode junction and this impacts their output.8.1 Abrupt: Abrupt diodes have a relatively sharp transition between the areas of the diode, as the name implies. They are able to give a higher Q than their hyper-abrupt relatives, while abrupt varactor diodes do not offer such a high tuning range or linear transfer characteristic. This results in a better oscillator phase noise output regulated by voltage. The other point to note is that in order to have the appropriate tuning range, abrupt varactor diodes may need a high tuning voltage, as certain diodes may need a tuning voltage for the VCO to differ up to 50 volts or slightly more. This can cause problems with supplying the drive circuits with a voltage supply with a sufficiently high voltage.8.2 Hyper-abrupt: There is a relatively linear voltage for hyper-abrupt diodes: the capacitance curve. As a consequence, in some applications, they give a very linear tuning characteristic that may be needed. They can also tune over a wide range, and can normally tune over an octave range with less than a 20-volt tuning voltage shift. They do not give an especially high Q standard, however. Since this will deduct from the tuned circuit's overall Q, this will mean that the output of the phase noise is as good as that which can be obtained using an abrupt varactor diode. Despite the apparent simplicity of the circuit, the voltage-controlled oscillator design is far from trivial. A design would also involve careful optimization of the levels of input coupled with the system and layout. The VCO's design will need to carefully balance the requirements of sometimes conflicting requirements, such as a large tuning range and low noise phase. The standards of efficiency that can be achieved are surprisingly good once the design has been completely configured and the design has been completed.Ⅸ FAQ1. What is a Voltage Controlled Oscillator?A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. 2. What is the use of VCO in PLL?VCO stands for Voltage Controlled Oscillator. PLL operation is simple. VCO creates a high-frequency clock that is divided by some factor. This divided frequency is compared against a stable, reference, frequency using a phase comparator and difference (in-phase or frequency) is converted into voltage and fed back into VCO.Depending on voltage difference VCO frequency will be higher or lower.For example, let’s suppose we have VCO generating 10000 at 5V and divide by 100 dividers. The reference frequency is 90. The phase comparator will subtract two frequencies, 100 - 90 = 10 and will produce some voltage proportional to the frequency difference. This voltage is fed back into VCO and will increase 5V to 6V. Voltage increase will result in frequency drop. The process will continue as long as VCO generated frequency is equal to reference, in our case 9000.From above we see PLL output frequency is: Out = Ref * DividerVCO in RF is produced using varicap diodes - diodes which capacity depends on reverse voltage. Varicap diodes are available with capacities ranging from 1pF up to 500pF and capacity change 2 - 20. How PLL is stable depends on the reference clock and a phase comparator. In the simplest case phase comparator are the XOR gate and RC filter. 3. Why is VCO better than DCO?Of course, the real answer depends on the application. But one important application for a VCO is to implement a so-called phase-lock-loop. In that application, the smoothly continuous frequency vs voltage characteristic of a VCO would allow the VCO to track some variable reference frequency much more precisely. A 'typical' DCO in the same application could only achieve a step-wise approximation to tight tracking. Another, historically more important, application of a VCO is as the primary component of an FM broadcast transmitter. Using a conventional DCO in this application would typically produce an unacceptable amount of weird, noisy distortion in the demodulated audio as the DCO control input attempted to track the audio signal. But yes, it is possible to conceptualize, and even practical to design, a DCO whose frequency control steps are so fine and rapid that, used in an FM broadcast transmitter, the listener would not notice the step-wise tuning of the carrier. 4. What is the function of a VCO voltage-controlled oscillator?A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. 5. How does voltage control oscillator work?A voltage-controlled oscillator is an oscillator with an output signal whose output can be varied over a range, which is controlled by the input DC voltage. It is an oscillator whose output frequency is directly related to the voltage at its input. The oscillation frequency varies from few hertz to hundreds of GHz. 6. How do you make a voltage-controlled oscillator?To make a VCO, the oscillator needs to be tuned by a voltage. This can be achieved by making the variable capacitor from varactor diodes. The tuning voltage for the VCO can then be applied to the varactors. 7. What is the output of VCO?The VCO has an output power level of -3 dBm into 50 Ω with phase noise of -101 dBc/Hz typical at 100 kHz offset. The control voltage range is 0.4 to 2.4 volts, and load pulling is typically 0.75 MHz, pk-pk. Power supply pushing is 280 kHz/volt (typical). 8. What is the VCO tuning range?The VCO is linearly tunable from 806 to 1,113 MHz with a 34% tuning range controlled linearly by the tuning voltage. The phase noise of the VCO is -100.4 dBc/Hz at 100-kHz offset frequency from a 903 MHz carrier. 9. What is VCO phase noise?Characterizing Phase Noise. The term phase noise is widely used for describing short-term random frequency fluctuations of a. signal. Frequency stability is a measure of the degree to which an oscillator maintains the same value. 10. Which is the input terminal in a VCO?It generates the square wave at the output whose frequency is determined by a control voltage. The first op-amp works as an integrator. The control voltage is applied at the input terminal and due to the voltage divider arrangement, half the control voltage is applied at the positive terminal of the first op-amp. 

Introduction: A Comprehensive Guide to Using a Multimeter in 2025When it comes to measuring instruments, the question often arises: how do you use a multimeter effectively? A Multimeter, also known as a VOM (volt-ohm-milliammeter) or DMM (Digital Multimeter), is the indispensable "Swiss Army Knife" for electronics. It is used to measure two or more electrical values—principally voltage (volts), current (amps), and resistance (ohms) in electronic and electrical circuits.In 2025, modern multimeters have evolved significantly. Beyond basic measurements, many now include features like capacitance testing, transistor checks, temperature sensing, and even Bluetooth connectivity for smartphone data logging. Whether you are troubleshooting a smart home device, checking automotive wiring, or testing a battery, the multimeter is your primary diagnostic tool.Multimeters are generally divided into two types: analog multimeters and digital multimeters (DMM). While analog meters use a moving needle, digital versions are now the industry standard, offering high accuracy, auto-ranging capabilities, and easy-to-read LCD or OLED displays. This guide is designed for beginners and will cover the basic parts, working principles, functions, and safety tips for using a multimeter in the modern era.Ⅰ What are the Parts of a Multimeter?The anatomy of a multitester generally includes a display (scale or screen), a selection knob, ports (jacks), and test probes. However, the interface differs between the older analog style and modern digital tools.Analog Multimeters: Use a microammeter with a moving pointer (needle) to display readings against a printed scale. They require the user to interpret the scale based on the selected range.Digital Multimeters (DMM): The current mainstream choice. They feature a numeric digital display, often with a backlight for dark environments. Modern DMMs may also include "True RMS" for accurate AC readings and auto-ranging features that automatically select the correct measurement scale for you.A common digital multimeter is composed of three main interface parts:1.1 The Display (Meter Head)On a digital multimeter, this is the LCD or LED screen where measurement values are shown. It often displays icons for battery life, high voltage warnings, and the unit of measurement (e.g., V, A, Ω). High-end models in 2025 may feature high-resolution color screens or bar graphs that mimic analog needles to show fluctuating signals.1.2 Measuring Circuit (Internal)Hidden inside the case, the measuring circuit converts incoming analog signals (voltage, current, resistance) into digital data. It is composed of precision resistors, an Analog-to-Digital (A/D) converter, and protective fuses to ensure safety during overload.1.3 Rotary SwitchThe central dial allows you to select the function (Volts, Amps, Ohms) and the range. In Auto-ranging multimeters, you simply select the function (e.g., DC Voltage), and the meter automatically adjusts to the scale of the signal. In Manual-ranging meters, you must select the specific range (e.g., 20V, 200V) yourself.Ⅱ Working Principle of MultimeterA Digital Multimeter (DMM) works by converting an analog input signal into a digital value using an A/D converter. The core logic involves comparing the input voltage against a reference voltage.To measure current and resistance, the multimeter actually uses voltage as the base reference:Current: The meter measures the voltage drop across a known internal shunt resistor.Resistance: The meter outputs a small, known current through the component being tested and measures the resulting voltage to calculate resistance (Ohm's Law).Modern DMMs use complex logic control circuits to manage the display, auto-ranging, and safety checks, ensuring that the reading on the screen is stable and accurate. Ⅲ Multimeter Operating ProceduresTo ensure accuracy and safety—especially with modern high-energy circuits—follow these steps:Safety Check: Inspect your test leads for damaged insulation. Ensure the multimeter is rated for the voltage you are testing (e.g., CAT III or CAT IV ratings for household mains).Select Function: Turn the rotary dial to the correct setting (Voltage, Current, or Resistance) before connecting the probes.Select Range: If using a manual-ranging meter and the value is unknown, always start at the maximum range and switch down to lower ranges to get a precise reading. Auto-ranging meters handle this automatically.Zero Calibration: For resistance measurements on analog meters, touch the probes together and zero the needle. Digital meters usually auto-zero, but you can check the "Rel" (Relative) mode on advanced models to null out lead resistance.Power Off for Resistance: Never measure resistance or continuity on a live circuit. Turn off the power to the device before testing.Probe Handling: Keep your fingers behind the finger guards on the test probes to avoid electric shock.Ⅳ Common Multimeter FunctionsMeasure Resistance (Ohms - Ω)Ensure the circuit power is OFF. Connect the test leads across the component (resistor, coil, etc.). Note: Measuring a component while it is soldered to a PCB may give inaccurate results due to parallel paths from other components.Measure Current (Amps - A/mA)Critical Step: You must physically move the red probe to the specific "Amps" or "mA" jack on the multimeter. The meter must be connected in series with the circuit (you must break the circuit and let current flow through the meter). Warning: Connecting a meter in current mode across a voltage source (parallel) will blow the meter's fuse.Measure Voltage (Volts - V)Connect the meter in parallel (across the component or power source). Ensure you select AC (V~) for wall outlets or DC (V=) for batteries.Detect Short Circuit (Continuity)Set the dial to the continuity mode (often marked with a sound wave symbol). Touch probes to two points. If resistance is near zero (a short), the multimeter will beep. This is excellent for checking broken wires or fuses.Non-Contact Voltage (NCV)Many modern multimeters (2020s era and later) include an NCV sensor at the tip. This allows you to detect the presence of live AC voltage in a wire or outlet without touching the metal contacts.Test ICs and ComponentsWhile multimeters can check supply voltage (VCC) and ground pins on Integrated Circuits (ICs), troubleshooting internal IC logic is often better done with an oscilloscope or logic analyzer. However, a multimeter is perfect for finding shorted pins. Ⅴ Multimeter Usage Tips1. Probe Safety: Never touch the metal tips of the probes during a test. Always hold the insulated handles behind the finger guards.2. Switching Gears: Never rotate the selection dial while the probes are connected to a live high-voltage circuit. This can cause internal arcing. Disconnect probes, switch modes, then reconnect.3. Battery Maintenance: If the multimeter will not be used for a long period, remove the internal battery to prevent leakage and corrosion.4. High Voltage Awareness: Be aware of the "CAT" rating of your meter. Do not use a CAT II meter for main service panels (which require CAT III or CAT IV ratings).Video: How to Use a Multimeter?Ⅵ How to Find Circuit Faults with Multimeter6.1 General Troubleshooting Strategy1. Visual InspectionBefore measuring, look for charred components, swollen capacitors, or loose wires. Touching components (cautiously) to check for overheating can also identify shorts.2. Voltage TracingMeasure the voltage at various points in the circuit starting from the power source. If voltage is present at point A but missing at point B, the fault lies between them (e.g., a broken trace or failed component).3. Hidden TroubleshootingIntermittent failures are often caused by "cold" solder joints or loose connectors. Continuity mode is vital here. Wiggle wires while testing continuity; if the beep stops, you have found a loose connection. 6.2 Measuring Techniques6.2.1 Voltage Measuring PointsTesting voltage against a "Ground" reference is the standard method. Connect the black probe to the circuit Ground (GND) and use the red probe to touch various test points (VCC, output pins). Deviations from the expected voltage (e.g., getting 2V on a 5V line) usually indicate a problem.6.2.2 Measuring Parameters Selection① Always check if you are measuring AC or DC. Measuring AC voltage while in DC mode (or vice versa) will give false readings.② For signal circuits, remember that standard multimeters measure "Average" or "RMS" voltage. They may not accurately show fast data pulses—an oscilloscope is required for that.③ Polarity: In DC mode, if you reverse the probes (Red on negative, Black on positive), the screen will simply show a negative sign (e.g., -12V). This is normal and safe for digital meters. Ⅶ How to Measure Current with Digital MultimeterMeasuring DC Current1. Insert the Red test lead into the jack marked "mA" (for low current) or "10A/20A" (for high current). Insert the Black lead into "COM".2. Turn the dial to the DC Current setting (A=).3. Break the circuit: You must physically interrupt the wire and place the multimeter probes in line with the circuit so current flows through the meter.4. Power on the circuit and read the value.Figure 1. Measuring Operating Current of a DC Relay If the reading is negative, your probes are reversed (current is entering the black probe). This does not damage a digital meter.Figure 2. Measuring DC Current in Series Measuring Current with an Analog MultimeterWith analog meters, polarity matters. If you connect probes backward, the needle will deflect to the left (below zero), potentially damaging the mechanism. Always ensure Red connects to the more positive side and Black to the negative side.Figure 3. Series connection with Analog Multimeter Figure 4. Reading the Scale on an Analog Multimeter Measuring AC CurrentThe process is similar to DC, but you must select the AC Current setting (A~). For high currents (e.g., household mains), it is highly recommended to use a Clamp Meter instead of a standard multimeter for safety. A clamp meter measures current via magnetic fields without breaking the circuit.Figure 5. AC Measurement Diagram Ⅷ Which is Better: Analog or Digital Multimeter?For 99% of users in 2025, the Digital Multimeter (DMM) is superior. It offers higher accuracy, higher input impedance (which means it doesn't affect the circuit you are testing), and easier readability. Analog meters are now a niche tool, primarily used by technicians who need to see real-time trends or rapid fluctuations that a digital digital might miss (though modern DMMs with "bar graphs" solve this).Analog MultimeterDigital MultimeterVisualizes trends/fluctuations easily via needle movement.Easy to read exact numbers; no parallax errors.Lower input impedance (can load down sensitive circuits).High input impedance (better for delicate electronics).Susceptible to damage from physical shock (drops).generally more rugged and durable.Often requires manual zeroing and range selection.Includes Auto-ranging, Auto-polarity, and specialized functions.Both meters have their place, but if you can only afford one, buy a Digital Multimeter. They are now available at very affordable price points without sacrificing essential accuracy. Ⅸ Best Multimeter Brands in 2025When selecting a multimeter, reliability and safety are paramount. Brands differ by their target audience: Professionals (industrial use) vs. Hobbyists (home use). Below are reputable brands recognized in the industry today.*Etekcity (Budget/Home)Mastech GroupInnova (Automotive)Klein ToolsKeysight Technologies (formerly Agilent)BrymenKaiweets / AstroAI (Budget)Fluke (Professional Gold Standard)ExtechAmprobeHioki Ⅹ Frequently Asked Questions1. What is a multimeter primarily used for?A digital multimeter is a diagnostic tool used to measure electrical values—principally voltage (Volts), current (Amps), and resistance (Ohms). It is standard equipment for electricians, automotive mechanics, and HVAC technicians. 2. What is "Auto-Ranging"?Auto-ranging is a feature on digital multimeters where the meter automatically selects the correct measurement range for the signal it detects. You simply select "Voltage," and the meter decides if it's millivolts or hundreds of volts. This saves time and prevents setup errors. 3. Why is "True RMS" important?True RMS (Root Mean Square) allows a multimeter to accurately measure AC voltage even when the sine wave is distorted (common in motor drives, HVAC systems, and computers). Non-True RMS meters are only accurate on perfect sine waves. 4. Can I use a multimeter to test a battery?Yes. Set the multimeter to DC Voltage (V=). Connect the red probe to the positive (+) terminal and black to negative (-). A fully charged 1.5V AA battery should read greater than 1.5V (usually 1.6V). If it reads below 1.2V, it is dead. 5. What are CAT ratings?CAT ratings (Category I, II, III, IV) define the safety level of the meter. CAT III or CAT IV is recommended for testing household wiring and mains power to protect against dangerous transient voltage spikes.

IntroductionThe mass air flow sensor, also known as the air flow meters, is one of the important sensors of the electronic jet engine. It converts the inhaled air flow into electrical signals and sends them to the Electronic Control Unit (ECU). As one of the basic signals to determine fuel injection, it is a sensor to measure the inhaled air flow into the engine.      CatalogIntroductionCatalogⅠ OverviewⅡ Structural PrincipleⅢ The Structure of the Valve Type Air Flow SensorⅣ Karman Scroll Air Flow SensorⅤ Measuring RangeⅥ Detection PrincipleⅦ Ultrasonic Karman Vortex Air Flow SensorⅧ Karman Vortex Type Air Flow Sensor for Pressure Change DetectionⅨ FAQⅠOverviewIn order to obtain the best concentration of the mixture under various operating conditions, the electronically controlled gasoline injection engine must accurately measure the amount of air inhaled into the engine at each moment, which is the main basis for the ECU to calculate (control) the amount of fuel injection.  If the air flow sensor or circuit fails and the ECU does not get the correct intake signal, it will not be able to control the fuel injection properly, which will cause the mixture to be too thick or too thin, and the engine will not operate properly. There are many types of air flow sensors in the electronic controlled gasoline injection system. According to their structure types, the common air flow sensors can be divided into blade (wing) type, core type, hot-wire type, hot film type, Karman vortex type, etc.                     Ⅱ Structural PrincipleIn the electronic controlled fuel injection device, the mass air flow sensor, which measures the amount of air absorbed by the engine, is one of the important components to determine the control precision of the system. When the control precision of the air-fuel ratio (A/F) of the air and mixture inhaled by the engine is specified as ±1.0, the allowable error of the system is ±6[%]~7[%]. When the allowable error is distributed to each component of the system, the allowable error of the air flow sensor is ±2[%]~3[%]. The ratio of the maximum value to the minimum value of the air flow rate inhaled by a gasoline engine is 40-50 in a natural intake system, and 60-70 in a supercharged system. In this range, the air flow rate of the sensor should be able to maintain a measurement accuracy of ±2~3[%]. The air flow sensor used in the electronic control fuel injection device should not only maintain the measurement accuracy over a wide measurement range, but also have excellent measurement response and can be measured. For pulsating air flow, the output signal processing should be simple. According to the different characteristics of the air flow sensor, the fuel control system is divided into L-type control for direct measurement of air intake volume and D-type control for indirect measurement of air intake volume (indirect measurement of air intake according to the negative pressure of the intake manifold and the engine speed).                                                           The microcomputer ROM in the D-type control mode stores in advance the intake air volume under various conditions based on the engine speed and the pressure in the intake pipe. The microcomputer is based on the measured operation. The intake pressure and speed in the state, referrring to the intake volume memorized by ROM, can calculate the fuel volume. The air flow meter used for L-type control is basically the same as the general industrial flow sensor, but it can adapt to the harsh environment of the car, but it is the response requirements for the rapid changes in the flow rate that occur during the throttle and the requirements for high-precision detection in the uneven airflow caused by the shape of the intake manifold before and after the sensor. The original electronic fuel injection control system did not use a microcomputer. It was an analog circuit. At that time, a valve-type air flow sensor was used, but several other air flow sensors emerged as microcomputers were used to control fuel injection.Ⅲ The Structure of the Valve Type Air Flow SensorThe valve type air flow sensor is mounted on the gasoline engine and installed between the air filter and the throttle. Its function is to detect the air intake of the engine and convert the detection results into electrical signals, which are then input into the microcomputer. The sensor is composed of an air flow meter and potentiometer. Look at the working process of the air flow sensor first. The air drawn in by the air filter rushes to the valve, and the valve turns to stop at the position where the intake is balanced by the return spring. In other words, the opening of the valve is proportional to the intake.  A potentiometer is also installed on the rotating shaft of the valve, and the sliding arm of the potentiometer rotates synchronously with the valve. The voltage drop of the sliding resistance is used to convert the opening of the measuring piece into an electrical signal, which is then input into the control circuit.Ⅳ Karman Scroll Air Flow SensorIn order to overcome the shortcomings of the valve type air flow sensor, that is, under the premise of ensuring measurement accuracy, expanding the measurement range and eliminating the sliding contact, a small and lightweight air flow sensor has been developed, namely the Karman Vortex Air Flow Sensor. The Karman vortex is a physical phenomenon. The vortex detection method and electronic control circuit have nothing to do with the detection accuracy. The air path area and the size change of the vortex column determine the detection accuracy. Because the output of such a sensor is an electronic signal (frequency), the AD converter can be eliminated when the signal is input to the control circuit of the system. Therefore, in essence, the Karman vortex air flow sensor is a signal suitable for microcomputer processing. This sensor has the following three advantages: high test precision, which can output linear signal and signal processing is simple; long-term use and performance will not change; because it detects volume flow, it does not need to correct temperature and atmospheric pressure.                                     The principle of flow detection of this air flow sensor is that when a Karman vortex is generated, it follows the change of speed and pressure. The basic principle of flow detection is to make use of the velocity change. The signal waveform output from the air flow sensor to the control module is shown in the figure. The signal is a square wave and a digital signal. The more air intake, the higher the frequency of the Karman vortex, and the higher the frequency of the output signal of the air flow sensor. The temperature and pressure compensation air flow sensor, mainly used for industrial pipeline flow measurement of medium fluid, such as gas, liquid, vapor and other media. It is characterized by small pressure loss, large range, high precision, and is almost unaffected by fluid density, pressure, temperature, viscosity and other parameters when measuring volume flow in working conditions.Features of the Karman Vortex Flow Meter                                There are no movable mechanical parts, so the reliability is high and the maintenance is small. The instrument parameters can be stable for a long time. This instrument adopts piezoelectric stress sensor, which has high reliability and can work in the working temperature range of -10℃~+300℃. There are analog standard signals and digital pulse signal outputs, which are easy to use with digital systems such as computers. It is a relatively advanced and ideal flow. The biggest advantage of the air flow sensor is that the meter coefficient is not affected by the physical properties of the measuring medium, and can be extended from a typical medium to other mediums. However, the frequency range is also very different because of the great difference between liquid and gas velocity ranges. In the amplifier circuit that processes the vortex signal, the passband of the filter is different, and the circuit parameters are also different. Therefore, the same circuit parameter cannot be used to measure different media.Ⅴ Measuring Range             Ⅵ Detection PrincipleOverhead power lines in the field whine when blown by the wind. The higher the wind speed is, the higher the sound frequency will be. This is because the air flows through the wire and forms a vortex. This phenomenon can occur in liquid, gas and other fluids, which can be used to make a vortex flow sensor. After the column is placed in the tube, two rows of vortices are formed, and the flow rate can be measured according to the frequency of occurrence of the vortices. Because the vortex turns into two parallel rows and alternates left and right, similar to the street lights on both sides of the street, it is called the vortex street. Because this phenomenon was first discovered by Karman, it is also called Karman Vortex Street.                                  Karman Vortex StreetⅦ Ultrasonic Karman Vortex Air Flow SensorThe ultrasonic air flow sensor is provided with two intake channels, the main channel and the side channel. The detection part of the intake flow is located on the main channel. The purpose of setting the side channel is to adjust the flow of the main channel so as to make the detection characteristics of the main channel present an ideal state. That is to say, for engines with different exhaust volume, one specification of air flow sensor can be used to cover a variety of engines by changing the cross-section size of the air flow sensor channel. The Karman vortex generator is composed of triangular columns and several vortex amplifiers on the main channel. On both sides of the place where the Karman vortex is generated, the ultrasonic transmitter and the ultrasonic receiver belonging to the electronic detection device are arranged oppositely. These two components can also be classified into the sensor. The electrical signal generated by the two electronic sensors is passed through the air. The control circuit (hybrid integrated circuit) of the flow sensor is shaped and amplified into an ideal waveform, and then input to the microcomputer. In order to detect vortices by ultrasound, sound-absorbing materials are glued to the inner wall of the vortex channel to prevent irregular reflections of ultrasonic waves.Ⅷ Karman Vortex Type Air Flow Sensor for Pressure Change DetectionThe vortex occurs alternately from both ends of the vortex generator, so the pressure at both ends of the vortex generator also alternately changes. This pressure change is guided to the mirror cavity through the pressure guide hole on the cone-shaped column on the downstream side of the vortex generator. In the mirror cavity, the mirror in the mirror cavity is tensioned with a very thin tension band, so distortion and vibration appear on the tension band. In addition, a leaf spring is used to apply appropriate tension to the tension band. Pressure changes other than vibration and scroll pressure are difficult to affect, so stable torsion and vibration can be obtained. The pressure formed by the vortex passes through the pressure guide hole to the reflector cavity, and the pressure changes synchronously with that in the reflector, and the reflector twists and vibrates in the tension band. The reflector is very lightweight and can operate even at low flow rates and very small pressure changes. On the upper part of the reflector, a light sensor composed of light-emitting diodes and phototransistors is correspondingly arranged. When the light emitted by the diode is reflected by the reflector and hits the phototransistor, it will become a current and output after the waveform circuit.Ⅸ FAQ1. What is the difference between the MAF sensor and the oxygen sensor?The MAF is the Mass Air Flow sensor and just as the name implies the sensor measures the mass of air going into the engine at the sensor (this is important because vacuum leaks or unmetered air is unaccounted for on the MAF sensor). Typically it uses a heated element and the air moving across the element cools it to "measure" the incoming air, however, vane style meters existed in the earlier days of electronic fuel injection. There are upstream and downstream oxygen sensors. The upstream sensor is responsible for checking the exhaust output of the engine. If there is too much fuel left in the exhaust the O2 sensor sends that information to the ECU and it will "trim" it out. If the O2 sensor samples the exhaust and there is too much oxygen in the exhaust stream then the sensor sends that info to the ECU and it will command more fuel. The downstream O2 sensor is present to monitor the condition of the catalytic converter(s). If it is out of range the ECU will flag it and the check engine light will illuminate. This is a very simple, quick, overview of the sensors but should give you a basic idea of their operation. 2. What are the symptoms of a bad mass airflow sensor?A faulty mass airflow sensor will cause problems similar to low compression or low vacuum, and will also show symptoms similar to when your vehicle has low fuel pressure from a faulty fuel pump. Here are some of the most common symptoms of a faulty mass airflow sensor:The engine is very hard to start or turn overThe engine stalls shortly after startingThe engine hesitates or drags while under load or idleHesitation and jerking during accelerationThe engine hiccupsExcessively rich or lean idling 3. How does a MAF sensor work?Installed in the intake pipe between the air filter housing and the intake manifold, most MAF sensors work on the hot wire principle. Put simply, a MAF has two sensing wires. One is heated by an electrical current, the other is not. As air flows across the heated wire, it cools down. When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases the current to the heated wire to compensate. The current is then changed to a frequency or a voltage that is sent to the ECU and interpreted as airflow. The quantity of air entering the engine is adjusted accordingly. 4. Can a car run without a mass airflow sensor?Well, the answer to that is no. If you disconnect the mass airflow sensor, then the car should keep running and still be able to start normally. This means that if your mass airflow sensor dies completely, then your car will stay running and surprisingly the car might run better without the mass airflow sensor. 5. Why a MAF sensor needs to be replaced?If the sensor gets dirty, it won’t be able to read the airflow. When the MAF sensor doesn’t work, the engine may idle roughly, hesitate, and have difficulty starting. It may even stall on you while driving, which is no fun. The most common cause for the sensor to become dirty is an air filter that doesn’t get replaced when needed. When the air filter is clogged, it allows more dirt and debris to slip by and accumulate on the sensor. Routine maintenance and air filter replacement can extend the life of your MAF sensor and ensure it continues to work correctly. While the exact timing varies based on where and how much you drive, a good rule to follow is every 10,000 to 12,000 miles. 6. What will a bad mass airflow sensor do?A contaminated or failed mass air flow sensor cannot measure the amount of air flow correctly. This causes the engine computer to miscalculate the amount of injected fuel. As a result, a bad mass air flow sensor causes various driveability problems, including a no-start, stalling, lack of power and poor acceleration. 7. Will a bad mass airflow sensor cause a misfire?If an oxygen sensor or mass airflow sensor is failing, it could give incorrect data to your engine's computer, causing the misfire. When a vacuum line is broken, it can cause a fuel-injected motor to misfire. ... Replacing a vacuum line that's gone bad can potentially resolve the misfire. 8. How long does it take for the mass air flow sensor to reset?When you change a MAF sensor, you need to disconnect the battery for about 10 minutes so the computer forgets the learned parameters and resets to the factory parameters. Then it goes into learn mode and may take a little while before it learns all the parameters of the new MAF sensor. 9. How long can I drive with MAF unplugged?When you unplug the MAF, the computer goes to a default value stored in your memory. Your fuel economy will probably suffer a little bit, but no big issues. You're OK for a week or two, but replace the MAF with a proper TDI unit. The long-term effect is that the car does not operate to its full potential. 10. Can you bypass a MAF sensor?There is a sensor on the air intake called the mass air flow sensor. This sensor calculates how much air to mix with the fuel. You can bypass the MAF sensor, and allow the O2 sensor to calculate how much air is needed. 

IntroductionA potentiometer is a three-terminal resistor with a sliding or rotating contact. It is an adjustable voltage divider with two static contacts and one moving contact. The moving terminal is a wiper that travels across the resistance element, usually in an arc controlled by a rotary knob. Rotating the knob gives a ratiometric division of the potential across the resistance element. Potentiometer generally used in speakers and receivers for volume control. In addition, it cannot directly control the motor because its power is too small. When potentiometer acting as a voltage divider, the absolute resistance of the potentiometer will not affect the output voltage, and its output voltage is proportional to the input voltage.Figure 1. Potentiometer StructureCatalogIntroductionⅠ Potentiometer WiringⅡ Potentiometer Symbol and Diagram DescriptionsⅢ Potentiometer Voltage Divider Circuit BasicsⅣ Potentiometer Resistance MeasuresⅠ Potentiometer WiringThe potentiometer can be used as a three-terminal component or a two-terminal component. The latter can be regarded as a rheostat. For a general potentiometer (three pins), the slider near the center which is a resistance wire. The two pins at both ends of the resistance wire are connected to the input and the ground (some are not connected), respectively. That is, one pin is connected to the input signal and the other pin is grounded. At this time, the resistance wire has a total resistance value on the two sections. You move the sliding piece to go across this resistance wire to get a variable resistance. If the input and output signals are reversed, the sliding direction of the slide is opposite to the resistance change.How to Wire a Potentiometer1) For a potentiometer (or a trimming resistors) with traditional pins (three pins), the resistance at both ends is fixed, and the resistance of the middle pin is variable. That is, the terminal on both sides of the potentiometer are total resistance, and the middle is changing. For example, the power supply is connect from any one contact on resistor sides and output from the middle contact, and the voltage changes with the rotation of the middle contact.Figure 2. Potentiometer Voltage Divider Output2) Although the resistance can vary with the slider, the total resistance value of pins is fixed. At this time, the potentiometer is equal to a current controller, and the selected current output terminals must be the sliding terminal. Commonly used potentiometers have poor resistance accuracy and poor temperature coefficient, but as long as the resistance of the potentiometer is uniform, so is the output voltage value.Figure 3. Potentiometer as Voltage Divider3) If a potentiometer used as a variable voltage divider, one contact connects to the input voltage, the middle contact connects to the output voltage, and the other contact can be grounded. When the rotary handle or sliding handle of the potentiometer take action, the movable contact slides on the resistor. At this time, an output voltage that has a certain relationship with the external voltage, wiper angle and travel stroke.4) If a potentiometer used as a variable resistor, one end connects to the input voltage, the middle end connects to the output, and the other end can be suspended or connected to the middle end to obtain a smooth and continuously changing resistance value.Figure 4. Potentiometer Connected as Variable Resistor As above mentioned, a potentiometer can be connected as a variable resistor, if you want to know more info, you can get it from The Differences Between Potentiometer and Adjustable Resistor. Ⅱ Potentiometer Symbol and Diagram DescriptionsNamePotentiometer SymbolDescriptionNormal PotentiometerUse RP (resistor potentiometer) to represent the potentiometer. The symbol in the figure mark the 3 pins of the potentiometer, indicating the chip pins.Potentiometer SwitchS1 is a switch attached to the RP, and S1 is controlled by the RP rotary handle. When you start to turn the handle, after the switch closes, this circuit is the same as a normal potentiometer. This kind of potentiometer is mainly used in volume control circuits with power switches.As a Variable ResistorThe potentiometer at this time can be regarded as a variable resistor.A Potentiometer with dual portDivide the 3 pins of the potentiometer into 4 ends to form a dual-port circuit. That is, terminals 1 and 2 input signals, terminals 3 and 4 output signals, and terminals 2 and 4 are common terminals, which usually connected to the ground of the line.Dual Gang PotentiometersIt has two single potentiometer circuit symbols, which are connected by a dotted line to indicate that the resistances of dual gang potentiometer are adjusted simultaneously, that is, their resistance values increase or decrease at the same time.Half Linear StrokeThis is a special dual gang potentiometer. Two potentiometer travel strokes are synchronized, but their resistance changes are not the same during adjustment. Only one mechanical stroke of this kind of potentiometer changes in resistance, and the resistance value of the silver zone is zero of another one. The silver zone with no resistance is indicated by shading in the circuit symbol. When the moving contact slides up from the middle, the moving piece RP-1 will enter the silver zone, and RP-2 will enter the varistor area; when the moving handle slides down from the middle position, the RP-2 will enter the silver zone, and RP-1 enters the varistor zone. This special potentiometer can be used in a stereo balance controller circuit (a control circuit in stereo equipment).With Central TapIt has one more pin than the ordinary potentiometer, that is, the tapping pin. The tapping pin is set at the middle resistance of the potentiometer, and the resistance between the tap and the two fixed contacts is equal. There are also potentiometers whose taps are not set in the middle position.Figure 5. Potentiometer CircuitsⅢ Potentiometer Voltage Divider Circuit Basics1) The resistor of the potentiometer is mostly made of polycarbonate synthetic resin. The following items should be avoided: ammonia, other amines, aqueous alkali solutions, aromatic hydrocarbons, ketones, lipid hydrocarbons, strong chemicals (excessive pH), etc., otherwise it will affect potentiometer performance.2) When soldering the potentiometer terminals, avoid using water-capacitive flux, which will cause metal oxidation and mold material. Using inferior flux, poor soldering may cause problems in soldering, resulting in poor contact or open circuit.3) If the soldering temperature of the terminal is too high or the soldering time is too long, it may cause damage to the potentiometer. The temperature range of the plug-in potentiometer is 235℃±5℃; the wire bonding type is 350℃±10℃, and the soldering point should be more than 1.5mm away from the potentiometer body. In addition, avoid heavy pressure on the terminals, otherwise it is easy to cause poor contact.4) During soldering, the height of the flux entering the printing machine board should be adjusted properly, and it should be avoided to affect the potentiometer. Because it will cause poor contact between the brush and the resistor, or result in noise.5) The potentiometer is better in the voltage adjustment structure.6) Avoid condensation or water droplets on the surface of the potentiometer, and avoid using potentiometer in a humid place to prevent insulation deterioration or short circuit.7) When fixing the screws of the rotary potentiometer, the strength should not be too strong to avoid poor rotation. For the direct-sliding potentiometer, avoid using too-long screws, otherwise it may hinder the movement of the sliding handle and even damage the potentiometer itself.8) In the process of putting the potentiometer on the knob, the pushing force should not be too large (don’t exceed the parameter index of the rated pushing and pulling force), otherwise it may cause damage to the potentiometer.9) The rotary force of the potentiometer will decrease as the temperature increases, and become smaller as the temperature decreases. If the potentiometer is used in a low temperature environment, it needs special low temperature resistant grease.Figure 6. Potentiometer Voltage Divider Circuit Connections10) If the shaft or sliding handle of the potentiometer is too long, it is easy to shake and cause the instability of the circuit signal.11) The carbon film of the potentiometer can withstand the ambient temperature of 70℃, and its function may be lost when the temperature is higher than 70℃.12) For a adjustable potentiometer, when the DC is allowed to pass through the movable contact, the problem of anodic oxidation may occur. In this case, it is best to connect the component with the negative end and connect the moving contact with the positive end.13) The load current of the adjustable potentiometer cannot be increased at will to keep circuit safety. And actual current measurement would be to put ammeter in series with the potentiometer in the active circuit.14) Do not exceed the rated power when using the adjustable potentiometer. For example, when the power dissipation exceeds the rated value, it will cause the potentiometer to overheat.15) A Potentiometer is sensitive if it is capable of measuring very small potential differences, and shows a significant change in balancing length for a small change in potential difference being measured.16) A DC potentiometer is created by dropping voltage across a set of resistors in series. Different resistors will produce different values. In AC potentiometer, one can use resistors or even inductors or capacitors as impedances which will drop voltages and provide a voltage less than applied voltage.17) If positioned the potentiometer wiper on the center of the resistor element then the voltage at the wiper is 50%; if the wiper is positioned 1/4 of the way from the negative node then the wiper voltage is 1/4th the entire voltage.18) Potentiometer nomenclature: It generally use the direct marking method. Letters and numbers are marked on the potentiometer shell to indicate their model, nominal power, resistance, and the relationship between resistance and rotation angle.If you have any interest, with a deep reading, you can get more info from What is the Voltage Divider Basic and Rule. Ⅳ Potentiometer Resistance MeasuresThe main checking requirements for the potentiometer are: ① The resistance value meets the circuit requirements. ② The connection between the center sliding end and the resistor is good, and the rotation is smooth. For potentiometer with switches, the switch action should be accurate, reliable and flexible. Therefore, the performance of the potentiometer must be checked before use.1) Resistance measurement: First, select the appropriate gear of the multimeter according to the resistance of the measured potentiometer. Whether the resistance between the two ends of the AC is consistent with the nominal resistance. Rotate the sliding contact, and its value should be fixed. If the resistance indicates infinite, the potentiometer is damaged.2) Then measure the contact between the center end and the resistor, that is, the resistance between the two ends of BC. The method is to set the ohm range of the multimeter in the appropriate range. During the measurement, slowly rotate the shaft and observe the reading of the multimeter. Normally, the reading changes steadily in one direction. If there is a jump, drop, or blockage, it means that the movable contact has failures.3) When the center end slides to the head or the end, the resistance value of the center end and the coincident end is 0 for an ideal state. In the actual measurement, there will be a certain value (generally determined by the nominal value, generally less than 5Ω), which is normal. Frequently Asked Questions about Potentiometer Voltage Divider1. How can a potentiometer be used as a voltage divider?Potentiometers can be used as voltage dividers. To use the potentiometer as a voltage divider, all the three pins are connected. One of the outer pins is connected to the GND, the other to Vcc and the middle pin is the voltage output. Basically, the voltage divider is used to turn a large voltage into a smaller one. 2. How does a potentiometer affect voltage?When the potentiometer resistance is decreased (the wiper moves downwards) the output voltage from pin 2 decreases producing a smaller voltage drop across R2. Likewise, when the potentiometer resistance is increased (the wiper moves upwards) the output voltage from pin 2 increases producing a larger voltage drop. 3. What is a dual gang potentiometer?It means two potentiometer combined on the same shaft, enabling the parallel setting of two channels. Most common are single turn potentiometers with equal resistance and taper. 4. How many volts can a potentiometer handle?100 voltsIf the potentiometer is rated at 1 Watt, you can only apply a maximum of 100 volts. I.e 10 mA. That applied to the voltage across the full 10000 ohms. That also means that you cannot pass more than 10 mA into the Wiper.