DC Fundamentals Unit 11 – Potentiometers and Rheostats
With a logarithmic (log) taper, one-half rotation changes the resistance by 10% of the total
amount. Resistance change is nonlinear (not in a straight line) with respect to shaft rotation.
There are three basic types of variable resistors: carbon composition, wirewound, and metal film.
Carbon composition types are available in wide resistance ranges, are inexpensive, and are
generally used in low power applications.
Wirewound types are available in low resistance ranges, are more expensive, and have wide
power ranges.
Film types are a compromise between carbon and wirewound elements in cost, resistance ranges,
and power.
NEW TERMS AND WORDS
potentiometer - A variable resistor connected with three terminals to provide a variable voltage.
rheostat - A variable resistor connected with only two terminals to provide a variable current.
taper - Variation in resistance of a variable resistor due to changes in the angle of shaft rotation.
linear - A change or control that varies at a uniform rate through the entire range of adjustment.
logarithmic - A change or control that varies at a different rate through its range of adjustment;
also called nonlinear.
EQUIPMENT REQUIRED
F.A.C.E.T. base unit
DC FUNDAMENTALS circuit board
Multimeter