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.
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 | 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 | -- | -- | -- | -- |
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.
Back to the Logic Design Page or the [Variable Resistors],
Potentiometer Manufacturers Page.
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