A throttle position sensor (TPS) is a sensor

Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

 used to monitor the position of the throttle

Throttle

A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...

 in an internal combustion engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

. The sensor is usually located on the butterfly

Butterfly valve

A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve...

 spindle so that it can directly monitor the position of the throttle valve butterfly.

The sensor is usually a potentiometer

Potentiometer

A potentiometer , informally, a pot, is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used , it acts as a variable resistor or rheostat. Potentiometers are commonly used to control electrical devices such as volume controls on...

, and therefore provides a variable resistance

Resistor

A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...

 dependent upon the position of the valve (and hence throttle position).

The sensor signal is used by the engine control unit

Engine control unit

An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...

 (ECU) as an input to its control system. The ignition timing

Ignition timing

Ignition timing, in a spark ignition internal combustion engine , is the process of setting the angle relative to piston position and crankshaft angular velocity that a spark will occur in the combustion chamber near the end of the compression stroke...

 and fuel injection

Fuel injection

Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....

 timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor

Carburetor

A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....

 systems).

More advanced forms of the sensor are also used, for example an extra closed throttle position sensor (CTPS) may be employed to indicate that the throttle is completely closed.

Some ECUs also control the throttle position and if that is done the position sensor is utilised in a feedback loop to enable that control.

Related to the TPS are accelerator pedal sensors, which often include a wide open throttle

Wide open throttle

Wide open throttle refers to an internal combustion engine's maximum intake of air and fuel that occurs when the throttle plates inside the carburettor or throttle body are "wide open", providing the least resistance to the incoming air...

 (WOT) sensor. The accelerator pedal sensors are used in "drive by wire

Drive by wire

Drive-by-wire, DbW, by-wire, or x-by-wire technology in the automotive industry replaces the traditional mechanical control systems with electronic control systems using electromechanical actuators and human-machine interfaces such as pedal and steering feel emulators...

" systems, and the most common use of a wide open throttle sensor is for the kick-down function on automatic transmission

Automatic transmission

An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...

s.

Modern day sensors are non contact type, wherein a magnet and a Hall effect sensor

Hall effect sensor

A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....

 are used. In the potentiometric type sensors, two metal parts are in contact with each other, while the butterfly valve is turned from zero to WOT, there is a change in the resistance and this change in resistance is given as the input to the ECU.

Non contact type TPS work on the principle of Hall effect

Hall effect

The Hall effect is the production of a voltage difference across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current...

, wherein the magnet is the dynamic part which mounted on the butterfly valve spindle and the Hall effect sensor

Hall effect sensor

A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....

is mounted with the body and is stationary. When the magnet mounted on the spindle which is rotated from zero to WOT, there is a change in the magnetic field for the Hall effect sensor. The change in the magnetic field is sensed by the Hall effect sensor and the voltage generated is given as the input to the ECU. Normally a two pole magnet is used for TPS and the magnet may be of diametrical type, ring type or segment type. The magnet is defined to have a certain magnetic field.