Electronic – simulate the temperature response of one thermistor by a different thermistor

resistorsthermistor

This sounds like an automotive question, but its really not.

I have a engine temperature sensor (presumably a thermistor, as it reduces resistance with increasing temperature). I need to mate this to a temperature gauge, but the gauge is calibrated for a different sensor with a different temp. response curve.

temp/ohm curves are known for both sensors (see graph)
enter image description here

For various reasons I can't replace the engine sensor. Also the gauge is a sealed unit, so lets assume I can't modify the gauge internals.

Is there anyway I can insert a circuit between the sensor and gauge, so the gauge 'thinks' its connected to the 'correct' sensor? Preferably a circuit of passive components as I don't have too much electronics experience.

Initially I assumed I might be able to do this by putting a suitable resistor in parallel with the sensor, but any resistor like that will only 'flatten' the response curve and as you see, response curve needs to be 'stretched'.

A couple of other factors to consider.

  1. I don't need super accuracy; +/- 3 deg C is fine
  2. I only this to work well in the range 85-105 deg C

Is this possible in principle and what is the general approach?

EDIT: More info

The red curve is given by: resistance(ohms)=114+6014*e^(T*-0.0396), where T=temp in deg C

Measured resistances from the existing engine sensor (blue line) is below. I would hope there is enough data there to predict the remaining values up to 105degC
(do themistors follow a standard curve?)

enter image description here

Best Answer

Use a microcontroller to measure the thermistor, then program a lookup table and make it control an electronic potmeter. Intermediate values can be calculated by interpolation.