Basic Principle of Adjustable Resistor
Adjustable resistor is also called rheostat. Adjustable resistor is a kind of resistor. The resistor value of adjustable resistor can be adjusted artificially to meet the needs of the circuit.
Common adjustable resistor mainly changes resistor value by changing the length of resistor access circuit. For temperature-sensitive resistor, it can also change resistance value by changing temperature, which is called thermistor. And for light-sensitive resistor, it can change resistor value by changing light intensity, which is called photosensitivity. Resistor; In addition, there are varistors, gas resistors and so on.
What is the function of adjustable resistor?
An adjustable resistor whose resistor can be adjusted. It is used in situations where the current of the circuit needs to be adjusted or where the resistor of the circuit needs to be changed. The adjustable resistor can change the characteristics of the signal generator, dim the light, start the motor or control its speed.
Mainly by changing its resistor and controlling the current in the series circuit, some electrical components can be protected (the size of the current is required).
The adjustable resistor is usually used in the circuit which needs to be adjusted frequently (that is, the resistor value does not need to change frequently), which plays the role of adjusting voltage, adjusting current or signal control. Its main parameters are basically the same as those of the fixed resistor.
Depending on the use, the resistor material of the adjustable resistor can be wire, sheet metal, carbon film or conductive liquid. For the general size of the current, commonly used metal-type adjustable resistors. In the case of low current, carbon film type is used. When the current is high, the electrolytic type is most suitable; the electrodes of the adjustable resistor are immersed in the conductive liquid. Potentiometer is a special form of adjustable resistor. It balances the unknown voltage or potential and measures the unknown voltage or potential difference. The more commonly used potentiometer is simply a resistor with two fixed joints, the third connected to an adjustable brush. Another use of potentiometers is for sound control in reverberation equipment.
Firstly, adjustable resistor is a kind of resistor. It can act as resistor in electronic circuit. Its difference from general resistor is that its resistor value can continuously change in a certain range. In some occasions where the resistor value is required to change but not always change, adjustable resistor can be used. Because of the structure and use of adjustable resistor, the failure rate is obviously higher than that of ordinary resistor. Adjustable resistor is usually used in small signal circuit, and large signal adjustable resistor is also used in a few occasions such as electronic tube amplifier.
Technical parameters of adjustable resistor
- 1.Nominal resistor
The nominal resistor of a variable resistor is the resistor between its two fixed pins. In order to facilitate production and meet the needs of practical use, the state has stipulated a series of values as product standards, which are the nominal series values of resistor.
- 2. rated power
Rated power refers to the power that can be sustained in normal operation. Its value is the rated voltage at both ends of the variable resistor multiplied by the rated current. If the working power is greater than the rated power, it may cause damage to the device.
Adjustable resistor characteristic parameters
1. Conformity, refers to the degree of conformity between the actual output function characteristics of variable resistors and the required theoretical function characteristics. The maximum deviation between the actual and theoretical characteristics is expressed as the percentage of the total applied voltage, which can represent the accuracy of the variable resistor.
2. Resolution depends on the theoretical accuracy of the variable resistor. For wire-wound varistors and linear varistors, the resolution is expressed as the percentage of the resistor change and total resistor caused by the moving contact moving one turn on the winding. For variable resistors with functional characteristics, the resolution is a variable because the resistor of each turn on the winding is different. In this case, the resolution of variable resistor generally refers to the average resolution of the maximum slope section of the function characteristic curve.
3. Sliding noise and sliding noise are the special noise of variable resistor. When changing the resistor value, due to improper distribution of resistor, improper matching of rotating system and contact resistance of the variable resistor, the moving contact will move on the surface of the resistor. Besides useful signals, the output of the variable resistor is accompanied by noise fluctuating with the signal. For wire-wound variable resistors, besides the contact noise between the moving contacts and the windings mentioned above, there are also resolving noise and short connection noise. Resolution noise is caused by the step change of resistor, while short connection noise is generated when the moving contact moves on the winding and short adjacent winding turns. It is proportional to the current flowing through the winding, the resistance of the winding turns and the contact resistor between the moving contact and the winding.
4. The mechanical life of the variable resistor and the mechanical life of the variable resistor are also called wear life, which are commonly expressed as mechanical durability. Mechanical durability refers to the total number of reliable movements of the movable contacts of variable resistors under specified test conditions, which is commonly expressed as “week”. The mechanical life is related to the type, structure, material and fabrication technology of variable resistors, and the difference is quite large.
Variable resistors also have rated power, allowable deviation of resistance value, maximum operating voltage, rated operating voltage, insulation voltage, temperature parameters, noise electromotive force and high frequency characteristics. The significance of these parameters is the same as the corresponding characteristic parameters of resistors.