Oil pressure sensor explained?

[njesper]

Well, I know that this sensor is from my alfa engine, but perhaps one of you guys can explain..

http://www.vegasvik.com/emden/gauges/pressure2.jpg

As shown on the sensor routing diagram, there are two pins on the sensor (where G - to the gauge, and WK - to the warning light, are connected).
1. Does it matter what pin is used for what? On the sensor iteself, there is no markings.. just two pin outs.

2. It says, when the pressure builds, the ground connection inside the sensor is cut, thus making the warninglight switch off (I get that so far), but according to the diagram, I don't get how the sensor can then transmit a signal to the gauge with only one cable and no ground?

Hope you guys can help me out here.

Best Jesper Colding

[JL]

The wire from the gauge is effectively an earth and the sender in the block provides progressive earthing relative to the pressure which changes the gauge reading. Hope this helps even if the explanation is a bit basic - maybe someone will have a more scientific explanation.

Regards
John

[njesper]

Hey John,

Okay, but then I still don't get why the warning lamp then turns off, when the sensor detects pressure??

Best Jesper

[suffolkpete]

Because the sensor provides an earth to the lamp via the WK terminal when there is no pressure.  This earth is disconnected when the pressure rises.  It does matter which termianal is which, you should be able to identify them with a test lamp or a multimeter.

[njesper]

Ahhh Pete,

That makes sense then. The terminals are two different sources of info! Super..
So i I use a multi meter, then the warning lamp terminal should make no resistance, and the other should make some restance?

[suffolkpete]

The warning lamp should make no resistance when the engine is stopped and will abruptly go to open circuit when you start the engine, as for the gauge terminal, that depends on whether the resistance goes up or down when the pressure increases.