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  Throttle-flap potentiometer




Assignment

It determines the respective angle of the throttle valve. In the case of central injection, this signal is used together with that of the Lambda sensor to calculate the strain, in the multi-point injection, it exists in addition to the air volume meter. If the throttle valve is connected with the accelerator, the throttle potentiometer can be used, e.g., for the recognition of the speed in which the pedal is operated. In addition, in case of an emergency, it can substitute for a possibly defective air-mass flow meter. In the case of Motronic with an electronic accelerator pedal, together with the servo-motor, it provides a control circuit for the throttle valve.

Function

For greater safety, two rotary potentiometers are connected with the throttle valve shaft. In addition, through various pre-resistors, these provide the characteristic curves of various areas. Occasionally one of the pre- resistors is also left out completely. It is now possible for the control device to recognise, not only short circuiting and feed interruptions, but also certain disturbing influences on the cables.

Interruptions in the circuit of a potentiometer can be determined by the so-called 'white-noise check'. Hereby, as many flap-positions as possible are made visible on a memory-oscilloscope, with which, if the resolution is high enough, even the smallest interruptions in the conductive path can be shown. This type of error cannot be detected by using a multimeter.

Where does the expression 'white-noise check' come from? Not from the vehicle tecnology, but originally from the electronic-technology. When this type of conductive path is tested, the oscilloscope can more often detect a higher resistance than is necessary for the coarseness of it's display. Resistance is generally measured by the drop in voltage. Thus, so many hundreds of voltages occur, and in the case of errors, also their distortions, that one describes them as 'white-noise' voltages, which presumably, can also be made audible. 04/10


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