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Temperature measurement gallery

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Nofossil, Sep 15, 2008.

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  1. Nofossil

    Nofossil Moderator Emeritus

    Joined:
    Oct 4, 2007
    Messages:
    3,398
    Loc:
    Addison County, Vermont
    Various devices for measuring temperature. Some of these have come up in discussions in different threads. A picture is worth a thousand words, so here goes:

    From left to right -

    1) Snap action thermal switch. Not adjustable, available in Normally Open and Normally Closed, in a variety of temperature settings. Simple, cheap. Can switch loads or relays directly. I used these before I built my controller.

    2) Platinum RTD (Resistance Temperature Detector, or something like that). Expensive, requires expensive and sensitive interface, extremely accurate and linear. I don't use them in real applications.

    3) Un-jacketed thermocouple. These are very cheap and tiny, but like all thermocouples they require special circuitry to get a reading.

    4) Jacketed thermocouple. In some variations, the jacket and thermocouple are electrically connected, in others they aren't. Available in many configurations. I use a pair of these with 1/8" diameter stainless sheaths for measuring combustion and flue temperatures.

    5) Glass-encapsulated thermistor with harness. I currently use these for most of my temperature measurement, with an additional heat-shrink covering over the bare wire. These are cheap and provide a strong signal, but they're highly nonlinear.

    6) Epoxy encapsulated thermistor. Water resistant, but no waterproof over long periods.

    7) Bare glass encapsulated thermistor, same type as #5.

    8) Analog Devices AD22103 low voltage analog sensor. Cheap, sensitive, but I've had a hard time getting them to work with long wires. Same physical package as #9.

    9) National Semiconductor LM35. Also cheap, but operates over wide range of supply voltage and seems to work better with long cables, but requires additional components (resistor and capacitor) as shown. I'll have prettier packaging if I end up using these. This on is 'live' in the picture. Temperature on the bench: 75.1 degrees. I'm looking at these to replace some or all of my thermistors.

    Missing from the gallery are any 1-wire sensors. At present, I don't have any I can lay my hands on.

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