Identification of thermistor circuit

Thread Starter

Kibirad

Joined Oct 18, 2021
24
Hi,
I’m replacing old house heating control unit. Part of this unit is outdoor temperature sensor. I would like to use existing wiring but the problem is there are only two wires. So I thought about using the existing circuit or replacing it with something similar with good precision in range from let’s say -20°C to 20°C. Current temperature sensor is most likely some kind of thermistor "bridge" circuit. I've tried to recognise some kind of known circuit in it. But it doesn't ring a bell.
The thermistors does have on them numbers 470 so they are probably 470R but I’m not sure. Can someone explain to me how should this circuit work? I’m also open to ideas about replacement for this temperature sensor but it would be probably wise to use something with large resistance change because lenght of the wires is also factor – length about 15-20m partly inside and outside so wire resistance with temperature dependence would be probably a thing. I was thinking about some combination of multiple thermistors to get large resistance change. Any ideas?
 

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sghioto

Joined Dec 31, 2017
3,710
If you are saying there are only two wires on the thermistor that would be normal.
Measure the resistance of the thermistor at known temperatures to get an idea of its range.
Are you planning on designing your own control circuit?
 

ericgibbs

Joined Jan 29, 2010
16,803
Hi K,
The resistors in parallel with the thermistors is an attempt at linearizing the Thermistor Resistance change versus Temperature change

E
This PDF will give you a basic idea.
 

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