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Potentiometer technology is well established and a proven method of position measurement used in a wide variety of industrial and automotive applications for absolute measurement of linear and rotary displacement.
Linear potentiometers are sensors that produce a voltage output proportional to the displacement or position of an operating shaft. The resistance element is supplied with a voltage (input) and the output signal is a linear function of the operating shaft displacement. Linear potentiometer resistance elements (tracks) are usually conductive plastic and the sensor housing is typically cylindrical in design.
Rotary potentiometers work on the same electrical principle as the linear, but the track is circular in construction and the operating shaft is rotated to give a proportional voltage output relative to the degrees of rotation.
Typically, the operational life span of a potentiometer is measured in the millions of cycles. The sensor is a simple low current measurement device that operates with only 3-wires. The output signal voltage achievable is dependant on input voltage. i.e. if you put 5V in, you get 5V out over the measurement range, 12V in, 12 V out, etc, up to the maximum input voltage specified by the manufacturer. Therefore a large output signal can be obtained over the measurement range with no additional amplification.
Other benefits of potentiometers over contactless sensors with internal electrics are that potentiometers have a predictable failure mode. As the potentiometer track and wiper combination wears through use, the output signal can exhibit spurious electrical noise due to the presence of a varying contact resistance caused by the wear points on the track. If this spurious noise condition occurs then the service engineer can receive early notice of potential problems and plan to replace the sensor before complete machine breakdown occurs. The failure mode of sensors with integral electronics is rarely predictable and over-temperature operation will usually result in the sensors failure.
The advantages of using potentiometer technology are:
- Very linear output signals
- Low current consumption
- Simplicity of operation (3 wire device)
- Large output signal
- No complex circuitry or electronics
- Over-temperature survival
- Lower cost than 'contactless' devices
A potentiometer is a contacting device and can be susceptible to the effects of extremes of shock and dither vibration and is not always the most appropriate sensor choice for high intensity use applications. In this case 'contactless sensors' should be considered.