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MG Midget and Sprite Technical - Wiring up of a temp gauge & sender

I have found an electric water temp gauge in the garage, and i want to see if it works. I also have a land rover temp sensor.

The gauge has 3 terminals on, marked +, -, & S
The sensor is a single spade, so earths through the body.

So it seems that the gauge connects to the battery, and then also connects to the sensor, which then also connects to earth. But it doesn't work. And the logic doesn't seem right. Is it right? Or am I doing it wrong?

Thanks
Matt
Tarquin

have you tried

12v + at the + terminal

earth potential at the - terminal

and sensor feed at the S terminal

?

Some electrical sensors need power "to work" and sensor "input/info" to "measure"

Just a thought, not familiar with these myself
Bill 1

The temp sensors work on change of resistance, as you then apply a set voltage to the circuit a current will flow. normally the gauge measures this current (milliampmeter) and displays it as temperature.
If however the voltage changes up or down slightly this would cause more or less current to flow and the reading would change slightly exactly the same as our fuel gauge which works on the very smae principle.

So modern gauges generally have a supply to them and internally have a voltage regulator to keep the voltage stable, then this voltage is applied between the "S" of the gauge and nuetral and when the S circuit is made to the sensor a reading is seen on the gauge.

If yours is the same then it would seem perhaps your VR is faulty try measuring the voltage across S and nuetral when the power is on?
Bob Turbo Midget England

I've checked the sensor resistance with a multi meter as follows:
boiling(ish) water: 334 ohms
room temp: 2000 ohms
bag of frozen peas: 8.0 on the 20k scale

Also, i've connected it straight to a 12v supply, maybe I should test it on the car with a supply from the dash loom to get a regulated 10v supply?

Bill, thats hwo I've wired it up but no joy.
Tarquin

This thread was discussed between 08/06/2011 and 09/06/2011

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