Overview of variable resistors - structure, operation and different applications

Overview of variable resistors —— structure 、 Work and different applications

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What is a resistor

• In the circuit , The resistor is a passive component at both ends , once electric current Flowing through it will stop electric current Flow and consume power . It uses diagrams in the circuit 1 The symbol in indicates . The ratio of voltage to current is called resistance , use [ Ohm's law ](https://en.wikipedia.org/wiki/Ohm’s_law#:~:text=Ohm’s law states that the,voltage across the two points.) Express , Pictured 2 Shown .

** chart 1：** Resistor symbol

** chart 2：** Ohm's law

• Ohm's law states that , When the temperature remains constant , Flow through the circuit resistor The current of is proportional to the applied voltage . therefore , Suppose there are two ordinary resistors terminal And it is logical that they have constant resistance , Because their resistance cannot be changed .

Definition of variable resistor

• seeing the name of a thing one thinks of its function , Variable resistor is a passive three terminal device , The resistance can be adjusted by the third terminal between the two terminals , Thus, the obstruction of current flow moves up and down . therefore , The variable resistance circuit symbol has an arrow representing the change in resistance . The electrical symbols of variable resistors are shown in the figure 3 Shown .

** chart 3：** Variable resistor symbol

** chart 4：** Variable resistor symbol

• The resistance of the variable resistor can vary from zero to a maximum through its third terminal . Take a closer look at the picture 4 Medium variable resistor Circuit diagram , You can see the terminal 1 and 3 There is a constant resistance between . terminal 2（ middle ） It is the only terminal with mobile ability . therefore , To change the resistance , You must use any side terminals with mobile terminals .

Working principle of variable resistor

• Variable resistors are widely used in circuits to adjust the value of current or voltage , Because the resistance of the variable resistor can be set to a certain value . The variable resistor allows you to adjust the voltage value by changing the resistance and keeping the current constant . To adjust the input voltage , Pictured 5 Shown , Connect the voltage source to the terminal 1 and 3. terminal 1 and 2 The output voltage between can be shown in Figure 6 The partial pressure formula shown in .

** chart 5：** Variable resistors are used as voltage dividers

** chart 6：** Partial pressure formula

Construction of variable resistor

• Although there are different types of variable resistors , But their working principle is the same . When checking the inside of the variable resistor , Pictured 7 Shown , At terminal 1 and 3 There is a fixed resistance called resistance track . terminal 2 Connect to knob , slider （ wiper ） Direct contact knob . The terminal can be changed by adjusting the knob in the middle 1 and 2 or 2 and 3 The resistance between , Pictured 7 Shown in a medium red circle .

** chart 7：** Variable resistor

Type of variable resistor

• There are different types of variable resistors , Their working principle is almost the same as that described in the previous sections . However , The terminal configuration and resistance value of the variable resistor can be adjusted relative to various environmental parameters . These different types of variable resistors include ：

Potentiometer

• As mentioned in the previous sections , variable resistor Usually used to control voltage or current . Potentiometer is one of the most popular types of variable resistors . They are preferred in applications that require voltage control . There are mainly two groups of potentiometers , Called mechanical and digital . Mechanical potentiometers such as linear and rotary potentiometers have accuracy problems in vibration environments . Due to the sensitivity problem of mechanical potentiometer , Digital potentiometers are usually used . One of the most basic uses of digital potentiometers is to provide resistance The problem of drift under challenging environmental conditions . Because the digital potentiometer can pass I2C Wait for the communication protocol to be adjusted , Therefore, when the mechanical resistance cannot be adjusted , They are also very useful .

Rheostat

• The structure of rheostat is similar to potentiometer . however , The moving terminal of the rheostat is short circuited with one of the side terminals , Pictured 8 Shown . Rheostat is preferred in applications that require resistance adjustment or current limitation .

** chart 8：** Rheostat symbol

Photosensitive resistor

• Photosensitive resistors are also called photosensitive resistors (LDR), Is a common variable resistor . Due to photoelectric effect , Their resistance varies with the intensity of the incident light . In an environment where light intensity changes , It is best to use photosensitive resistors .

Force sensitive resistor

• seeing the name of a thing one thinks of its function , The resistance of the force sensitive resistor will change with the applied force level . They are usually used in robot applications , For example, inside the fixture of the robot .

Thermistor

• The resistance of thermistor changes with temperature . There are two types of thermistors , It is called negative temperature coefficient (NTC) And positive temperature coefficient (PTC) Thermistor .PTC The resistance of thermistor is proportional to temperature , and NTC The resistance of thermistor is inversely proportional to temperature . In different industrial applications where temperature change detection is crucial , Thermistor is the first choice .

Hygrometer

• seeing the name of a thing one thinks of its function , The resistance of humidity sensitive resistor will change with the change of humidity . Hygrometers are used in many Internet of things (IOT) Equipment to detect environmental changes .

Application of variable resistors

• Many devices in our home / Variable resistors can be found in electronic products . Some of them include radios 、 The speaker 、 Microphone 、 TV 、 oscillator 、 Smart home control equipment . Potentiometers are usually used in household appliances that require speed or volume control .
• Rheostats are used where current or resistance levels need to be adjusted . A common example is the dimming of lights . All in all , Variable resistors are popular in applications that require voltage control or current regulation .