A potentiometer is a mechanically variable resistor which, in EFI applications, is normally a film-type.
It can be linear, or circular, in construction, and has 3 electrical connecting points. Two are at the ends of the resistor, and a third is attached to a center sliding contact, arranged to move across the resistor. A reference voltage is applied to the resistor, so that a steady current flows through it.
As the center sliding contact moves across the resistor, it measures the voltage at the point it is in contact with, and provides a reference voltage for that position.
In automotive applications, the circular form is commonly used as a throttle position sensor, with the center contact attached to the throttle plate. The throttle plate position can then be monitored by the control unit.
