402388-11W

The 402388-11W potentiometer is an automation device that is manufactured by Allen-Bradley. The device is a potentiometer containing carbon elements whose advantages include low cost and relatively low noise output, even during adjustments. The resistive range of the carbon elements reaches as high as 20 megohms and as low as 10 ohms. The total resistance tolerance is typically plus or minus 10%. The end resistance is usually high when the presence of substantial contact resistance in carbon elements limits the device’s application. Note that carbon elements do not handle moisture well, and their load stability is not as good as that of cement. In the space of a year, molded carbon elements can be expected to shift as much as 5% and they may need to be replaced. The 402388-11W potentiometer also has a conductive plastic element with low-cost, low-contact resistance variation, and an extensive rotational life. The temperature coefficient of carbon is positive.

The magnitude of the temperature coefficient differs within the various types of available carbon potentiometers like the Allen-Bradley 402388-11W potentiometer. Molded carbon units may contain a TC range of -2000 ppm degrees Celsius to -8000 ppm degrees Celsius although deposited carbon elements have a TC of about -1000 ppm degrees Celsius. A temperature coefficient as low as  -200 ppm degrees Celsius is not available in conductive plastic units. The 402388-11W potentiometer also contains metal film elements that make it possible to vacuum deposit a fragile layer of metal alloy in the device to form a resistance element. This alloy is typically a member of the nickel-chromium alloy family and it is used to deposit a layer that is 100 to 2000 angstroms thick. Metal film elements are useful only for lower resistance values, and the total resistance available is from 10 ohms to 20 kiloohms.