# Is is possible to produce a resistance that represents the average of two thermistors?

For example, if I want to connect 2 thermistors to a thermostat in a circuit and then return the average resistance between the two of them to the thermostat's ADC.

• Measure Thermistor A. Measure thermistor B. Add the two resistances and divide by two. That's an average of two thermistors but i suspect you mean something that you haven't quite explained yet. Or maybe I'm being stupid? Apr 11, 2013 at 14:31

I'm assuming this thermostat is a fixed device you don't have control over, so suggestions to use a different fixed resistor in the bridge or digitally dividing by two are useless.

No, there is no simple way to take two thermistors of the intended value and have them average directly. However, there are several things you can do:

1. Get two thermistors with twice the nominal resistance and connect them in parallel.

2. Get two thermistors with half the nominal resistance and connect them in series.

3. Get four thermistors of the nominal resistance and connect them series-parallel. That will allow you to sortof average the four measurements. simulate this circuit – Schematic created using CircuitLab

Use four thermistors. Two of type A, two of type B. Put the A in series. Put the B in series. Put the two strings in parallel. Viola! Total resistance is the average of A and B.

By type A and type B, I mean type A are thermistors at temperature A, type B are thermistors at temperature B.

You get average of the conductance, not resistance. But it represents the average of the temperatures, within limits.