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steam room temperature sensor

I have a steam room with a 25 year old Amerec Steam generator.  It still works well, but I have a concern about the temperature sensor.

The manufacturer claims to have no data on these old units, but states that the temperature sensor will fail over time and accumulated heat.  They said it was "some sort of homemade thermistor".  It is clearly encapsulated in an aluminum block - I assume to dampen temperature changes.  They said that they have no data on it and it cannot be replaced.  The connection to the control system is a simple 2 wire RCA plug.

Is there some service that chan characterize this device for me, so I could find/create a replacement when it ultimately does fail?  I've measure the resistance at 60 and 100 deg F, and they were 29.1 and 28.3 k respectively.

I'm also thinking of hooking a potentiometer up to the control in place of the sensor and trying to elucidate the control curve that way.  Does this make sense, or is there something I'm missing here?

Many thanks in advance for any help!



  • M0GRP
    M0GRP Member Posts: 1
    Testing Thermistors


    you've gone about testing it in the right way, just not completed the process.

    Most thermistors are spec'd at 25 degrees C and there are lots of different types available.

    What you need is at least three points on the scale - ice, boiling water and somewhere betwee are the minimum.

    Knowing one value isn't enough because they aren't a linear device and it depends what process they were made with as to how the resistance varies.

    I'd guess the one you have is an NTC device - that means the resistance drops with increasing temperature and assuming it's one of the common parts, it's probably 100k at 25 degrees.

    Once you have the three points, there are lots of component suppliers ( Newark, Digikey, Mouser,etc. ) who will sell you one, but more importantly, they will let you look at the data sheets to find a match.

    At the very least they will list the resistance every 5 degrees to let you make a comparison.

    Be aware that Thermistors aren't a calibrated device and there is always a 5% tolerance on the nominal resistance - that could lead to problems in a steam room, so be careful.
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