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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
Contacts
As you can probably imagine, the contact or wiper has a significant effect on many potentiometers. Contact resistance, contact resistance variation (CRV), resolution, noise, power rating, operational life, and stability (with shock and vibration) are all influenced by the design of the moveable contact.
The physical form of the wiper takes many shapes. The contact generally used with wirewound resistance elements is like that in Figure 2.43.
Its shape guarantees that it will make physical contact with more than one turn of resistance wire. The contact material used is hard enough to minimize contact wear without having an abrasive quality which would shorten element life.
Figure 2.43
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Figure 2.44
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The contact pictured in Figure 2.44 is typical of those used with non-wirewound elements. They are usually multi-fingered in order to decrease contact resistance.
Moveable contacts are generally made of a metal alloy which provides its own spring force, thus simplifying the mechanical design of the assembly. Spring pressure aids electrical conduction by helping to break down insulating films which form on metal contacts and element surfaces. Spring pressure also helps to keep the potentiometer working during shock and vibration.
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