Potentiometers - A potentiometer is a 3-wire device that is used to vary voltage in a circuit. This signal must be converted to digital form before it can be read by the computer's microprocessor. Most potentiometers have a 5V power feed, a ground circuit, and a feedback line to the computer which will vary between approximately 0.5V and 4.5V representing the position of the object being monitored.
Examples of potentiometers:
- Throttle Position (TP) Sensor - Used as a major input for both engine and transmission control on vehicles with a throttle cable..
Accelerator position (APP) sensor - Used as a major input for both engine and transmission control on vehicles without a throttle cable.
Exhaust Gas Recirculation (EGR) valve pintle position sensor. Used as an input to indicate EGR flow rate.
Suspension system position sensor - Used by vehicles with electronic suspension systems to monitor vehicle height changes. The control of the stiffness of the shock absorbers or struts will be affected by this input.
Seat position sensor - Used for memory seat positioning and vehicle personalization systems.
Tilt-telescoping steering column position sensor - Used for memory steering column positioning and vehicle personalization systems.
Rear view mirror position sensor - - Used for memory mirror positioning and vehicle personalization systems.
A rheostat is a 2-wire variable resistor that is used to vary current in a circuit. Most older vehicles use a rheostat to monitor the float position level in the gas tank. A typical instrument panel lamp dimmer is an example of a rheostat that monitors the position of the dimmer switch. This type of signal must be converted to digital form before it can be read by the computer's microprocessor.
A Linear Voltage Differential Transformer is a 2 or 3-wire device depending on the manufacturer. LVDT's are typically used for suspension system height monitoring. A LVDT monitors the position of an object by watching the inductance of a transformer in the sensor. As an object physically moves, the metal core of the transformer moves with it. This changes the amount of voltage and current that the transformer's primary coil induces into the secondary coil. This changing voltage is either directly read by a computer or converted into a varying voltage feedback signal to a computer.