Senders (Sensors) - Audi A8 292 Service

System components

Senders (sensors)

Compressor temperature sender G290
Construction:
An NTC resistor is housed in a small glass
case.
Function:
The sender records the temperature of the
cylinder head compressor.
Its resistance decreases sharply as the tem-
perature rises (NTC: negative temperature
coefficient). This change in resistance is ana-
lysed by the control unit. The current temper-
ature calculated in each case determines the
maximum compressor running time. The
sender cannot be replaced separately during
servicing.
Temperature sensor
292_017
Pressure sender G291
Construction:
The sender is cast in the solenoid valve block
and is inaccessible from the outside.
Function:
The pressure sender measures the pressure
of the front and rear axle struts or the accu-
mulator (depending on how the solenoid
valves are actuated, see pneumatic diagram).
The G291 employs a capacitive measuring
technique:
The pressure (p) to be measured causes a
ceramic diaphragm to deflect. This deflection
changes the distance between an electrode
(1) attached to the diaphragm and a station-
ary counter-electrode (2) on the sender hous-
P
ing.
The electrodes together form a capacitor. The
smaller the distance between the electrodes,
the greater the capacitance of the capacitor.
This capacitance is measured by the inte- 2 1
grated electronics and converted to a linear
output signal.
292_024
20