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Thread: Ambient Temp Thermistor Help

  1. #1
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    Ambient Temp Thermistor Help

    I added a MF52-103 thermistor across probe 3 jack to sense ambient temp but it reads 185 degrees at room temp. I have the resistance set to 10000. Any suggestions?

  2. #2
    TVWBB Guru Steve_M's Avatar
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    You need the Steinhart-Hart values.

    Try these values in the Probe Coefficients custom settings.

    A: -0.000950054
    B: 0.000589776
    C: -0.000001428

    I grabbed these values from https://forum.arduino.cc/index.php?topic=614371.0

  3. #3
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    Thanks for the info. I calculated the S-H parms by using an online calculator. Inputs were three resistance values at known temps. Near freezing. near boiling and room temp. The resulting parms didn't give accurate temp readings.

    https://www.thinksrs.com/downloads/p...calculator.htm

  4. #4
    TVWBB Honor Circle Bryan Mayland's Avatar
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    That calculator works for other thermistors, because I've used it before. I'd say make sure the values in the config are close to what the calculator came up with (HeaterMeter didn't misinterpret them so like 1.428e-06 didn't become just 1.428). There will be some loss of precision due to how floats are stored in RAM, but they should round to having at least 3 significant digits accurate. Also be sure to keep your "Resist" to 10000 in the config because that's the fixed resistor that's installed in HeaterMeter, not the resist of the probe / ambient thermistor.

    EDIT: I should say also be sure you use the calculator in Celsius.
    I'm that HeaterMeter guy what ruins everybody's free time.

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