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Insight - How Preset works

Written By: 

Ashok Sharma
 
Preset is a small variable resistor generally used to provide a variable resistance in a circuit in order to tune the circuit. They are directly mounted on the PCBs. A screwdriver or similar tool is required to adjust them.
 
Preset - Small Variable Resistor
 
A 20K-ohm metal preset is shown in the image above i.e. the maximum value of resistance that we can give in a circuit by using this preset is 20k ohm.
 
Top Plate of Preset
 
The rectangular space between the cover of the preset is used to rotate it on the track. Upper side of the cover has a slight curved dent which connects the resistive strip with third leg (upper leg) of the potentiometer.

Resistance Track

Resistance Track of Preset
 
The black arc seen in the picture is a resistance track.
 
 
Parts, components of preset
preset parts
 
Above images shows the components of preset that are used to structure it.
Working of presets is quite simple. It works by having a resistive track and a small plate having dents to short the track. This small plate can be rotated using a screw driver or some similar tool. Position of the dents on the track determines the amount of resistance that is to be used in the circuit.

Comments

nice information very usefull 

Thanks........

thank you