Variable Resistors

Variable Resistors

Thermistor

Engine Temp Dual Thermistor:

The resistance of materials can vary with changes in temperature; therefore, resistors can have a changing resistance value dependent on temperature.
A Thermistor is a resistor that can achieve large changes in resistance with small changes in temperature.
Thermistors are normally of the NTC (negative temperature coefficient) type. As the temperature increases the resistance decreases. BMW also uses PTC (positive temperature coefficient) type thermistors. In a PTC the resistance increases as the temperature increases.

Potentiometer







A Potentiometer (pot.) is a variable resistor capable of changing resistance values. Potentiometers have three terminals. One of the terminals is supply voltage, usually 5 volts. One of the terminals is the control module ground, and the third terminal is for the input signal into the control module. (Output from the Pot.) Potentiometers are used to measure mechanical movement. (e.g. Vane air flow meters, Throttle position sensors and Pedal position sensors.)

Rheostat

A Rheostat is similar in operation to a potentiometer except a Rheostat only has two connectors. This arrangement allows the resistance to be varied between those two connectors.

Electric Motors




DC motors are similar to DC generators. They may be described as generators run backwards. When current is passed through the armature of a DO motor, a torque is generated by magnetic reaction and the armature revolves.

Stepper Motors

Stepper Motors behave differently than standard DC motors. Unlike DC motors which spin freely when power is applied, stepper motors do as their name suggests, they step or rotate incrementally a little bit at a time. While DC motors need higher speeds to produce higher torque, stepper motors provide their highest torque at their slowest speeds. Stepper motors also have holding torque, the ability to resist movement by outside forces.
Steppers are driven by the interaction (attraction and repulsion) of magnetic fields. The driving magnetic field rotates as strategically placed coils are switched on and off. This pushes and pulls at permanent magnets arranged around the rotor that drive the output shaft.