Potentiometer For Position Transducers

Thursday, November 30th, 2017 - Displacement, Resistive Transducers, Transducer/Sensor

Potentiometer For Position Transducers

A potentiometer converts a mechanical input, namely the physical position of its wiper terminal, into an electrical signal by the simple principle (If a potential divider, as illustrated by Figures 1 and 2 and eqns (2.1) and (2.2).

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Figure 1 Angular position measurement using a potentiometer

Linear position measurement using a potentiometer

Figure 2 Linear position measurement using a potentiometer

Potentiometer For Position Transducers Formula

(Given that the supply voltage Vs, the total resistance value Rtot the total angular displacement θtot. and the total linear displacement Xtot . are known constants. )

The resistive track can be made of a carbon film to reduce cost, or a cermet (conductive ceramic) film to increase the resolution and reduce noise, or a wound metal wire to allow higher power dissipation. The main advantages of potentiometers as position transducers are low cost, small size and versatility of operation (for example, it can easily provide logarithmic or quadratic functions), whereas the two main drawbacks are, firstly, that it is an inherently analogue device and therefore requires additional hardware, usually an analogue-to-digital converter (ADC), to interface it to a computer and, secondly, that its principle of operation requires the wiper to actually touch the main resistive medium, which makes it prone to mechanical wear and tends to limit its operational life.

Optical transducers are therefore slowly replacing the potentiometer in those position measuring applications which require very long operational life. Nevertheless the potentiometer is still widely used as a position transducer in most engineering applications in view of its ease of operation and versatility, small size and low cost.

An example of the potentiometer’s popularity can be found in its use within the control structure of some educational and light industrial robots. The potentiometer’s low cost and small size, in fact, allows full exploitation of the high torque-weight ratio of permanent-magnet d.c. motors, which has led some manufacturers to produce integral, lightweight and powerful pulse position (PWP) controlled d.c. servo units. For further details on such a device on Interfacing.

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