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Introduction - Basic Potentiometer Theory • Resistors • Building Potentiometers • Modern Variable Resistive Devices • Applications Modes • The Parts of a Potentiometer • Resistive Elements • Cermet • Conductive Plastic • Hybrid Elements • Terminations • Contacts • Electrical Parameters • Total Resistance • Minimum Resistance • End Resistance • Contact Resistance • Contact Resistance Variation • Equivalent Noise Resistance • Output Smoothness • Adjustability • Temperature Coefficient • Resolution • Conformity • Linearity • Power Rating • Summary of Electrical Parameters • Useful Terms
Contact Resistance Variation
Contact Resistance Variation (CRV) is the variable resistance between the wiper and resistance element when the wiper is energized with a specified current and moved over the adjustment travel at a constant speed (non-wirewound only). CRV is due to changes in the:
- thickness of the element
- impurity in the element, and/or
- contact pressure that changes as the wiper element moves across the surface of the resistive element
Figure 2.47 is an oscilloscope photograph of CRV.
Figure 2.48
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The photograph shows two complete revolutions of a single-turn potentiometer. The extreme variations at the ends are due to the wiper movement onto or off of the element. They are not considered to be CRV. As you can see from the photograph, this device just meets a 1% CRV spec.
The CRV spec applies to cermet and conductive plastic elements as well as hybrid elements. Wirewound elements are rated by a different spec, known as Equivalent Noise Resistance (ENR).
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