Wirewound Potentiometer per MIL-PRF-19

Potentiometer Design Information

Resistors can be combined with potentiometers to change the way they vary the resistance.
It's a cost effective way to obtain an output characteristic, although some experimentation might be required.
The resistors are being used to change a potentiometer with a linear taper, but audio or logarithmic tapers are also available.

Potentiometer Shunt Design Example
Potentiometer Shunt Resistor

Applying a Shunt resistor to change a Potentiometer characteristics
Green is the Potentiometer, Red, and Blue are the change due to the shunt

There are three types of Variable Resistors, each of which consist of a three terminal resistor; two fixed end leads and one lead attached to a variable tap.
The variable tap is movable to change the resistance, between the tap and terminal.
Potentiometer: Designed for frequent changes ~ a volume control
Trimmer: Designed for less then frequent changes [occasional]~ a trim pot on a PCB to finalize a circuit resistance. [Trimmer Resistor packages]
Rheostat: A three terminal potentiometer which only uses two terminals [center tap and one end].
The material used determines the Variable Resistor's operational range [temperature and wattage]. The material may be;
Carbon composition, Resistive wire [Wirewound], Conductive Plastic, and Cermet [a mixture of ceramic and metal].

Also refer to Terms used with Resistors.

Potentiometer Types

Types of Potentiometer and Characteristics
Potentiometer Types Carbon Composition Cermet Conductive Plastic Wirewound
Humidity Sealed Immune Large Change --
Temperature Sealed Very Good Large Change --
Wattage Medium Low/High Low Medium/High
Resistance Range High High High Low
Resistance Value 50ohm - 50Mohm 10ohm - 5Mohm 100ohm - 5Mohm 10ohm - 100Kohm
Frequency Range -- High -- Very Low
Tolerance -- -- -- --

Potentiometer Temperature Range / Derating

Component Derating Guidelines

Variable Resistor Material type vs. Operational Temperature Range
Potentiometer Derating Graph

Military Standards specifying variable resistors;
MIL-PRF-12934; Precision Variable, Wirewound Resistor
MIL-PRF-19; Variable, Wirewound Resistor
MIL-PRF-22; Power Type, Variable, Wirewound Resistor
MIL-PRF-22097; Adjustment Type, Variable, Non-wirewound Resistor
MIL-PRF-27208; Variable, Wirewound Resistor (Nonprecision)
MIL-PRF-39002; Semi-Precision Variable, Wirewound Resistor
MIL-PRF-39015; Lead Screw Actuated Variable, Wirewound Resistor
MIL-PRF-39023; Precision Variable, Nonwirewound Resistor
MIL-PRF-39035; Adjustment Type, Variable, Non-wirewound Resistor
MIL-PRF-94; Variable Composition Resistor

Note the military does not use the term trimmer, as that term tends to describe the usage of a variable resistor.

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Modified 3/05/12
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