The Influence of Lubrication on Electrical and Mechanical Parameters of Potentiometer Resistive Element
Fixed resistors are usually protected against environmental influences. For this aim, special lacquers are used. Much of the environmental qualities of such a resistor are directly related to its enclosure.The resistive element of the potentiometer cannot be protected in the same way. The producers of quality potentiometers, especially thin film ones, designed an effective seal of their housing but it leads to an increase in production costs.The first researches on thin film resistive elements for potentiometers, proved the major sensitivity of the unit to moisture cycling, because of high water chemisorption on the resistive element surface.The chemisorption effect has the major influence on the temperature coefficient of resistance (TCR), because at a higher temperature, water desorption is occuring and the resistance of the film is undergoing a change.However, the IEC Standard recommends dry out of resistive elements before TCR measurement; the potentiometer users feel that total resistance changes as a sum of temperature change and drying out change.The present paper deals with trials to eliminate this disadvantage of thin film potentiometers by protection against moisture.The protective coating should, because of its affinity to the resistive film, form durable protection against environmental influences, but should not increase the contact resistance of the wiper (CRV). Such a coating also should not increase the friction coefficient of the wiper.To verify the hypothesis that polar lubricants can play a part in protective coating of thin film potentiometers, several different lubricants have been examined.