Linear Potentiometer

A linear potentiometer transducer consists of a potentiometer, which is short circuited by a slider. The other end of the slider is connected to a slider arm. The force summing device on the slider arm causes linear displacement of the slider causing the short circuit of a certain portion of the resistance in the potentiometer. Let the whole resistance positions on the potentiometer be ABC. Let the resistance position caused by the slider movement be BC. As the movement of the slider moves further to the right, the amount of resistance increases. This increase in resistance value can be noted according to the corresponding change in the linear displacement of the slider. The change in resistance can be calculated with the help of a Wheatstone bridge.

Another easy method than calculating the resistance with the help of a bridge connection is to connect a constant current source in series with the potentiometer. Thus a voltage will be developed. This voltage can be measured and hence the resistance, R = V/I.

Advantages

Ø  Easy to use

Ø  Low cost

Ø  High amplitude output

Ø  Easily available

Disadvantages

Ø  Limited band width

Ø  Inertial loading

Ø  Number of operating cycles are limited

Ø  A huge force may be required for the slider movement.

Ø  Can produce unwanted noise due to alignment problems, wear and tear of the sliding contact. This may also affect the total life of the device.

Applications

Ø  Linear displacement measurement

Ø  Rotary displacement measurement

Ø  Volume control

Ø  Brightness control

Ø  Liquid level measurement using floats