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Faulty temperature sensor

Discussion in 'Electronic Basics' started by Jurgen Bauer, Dec 25, 2004.

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  1. Jurgen Bauer

    Jurgen Bauer Guest


    I would like to check out a temperature sensor for my central heating
    cylinder. 2 cables coming from the sensor.

    What voltage do I need?
    What should change with the rising temperature?

  2. Jamie

    Jamie Guest

    i don't know but do you mean 2 wires or 2 cables?
    there is a difference.
    cables have 2 or more wires and even conductors
    like drain wire.
    wire on the other hand is a single conductor with
    some kind of insulation around it.
    in any case.
    it's hare to say what type you have ?., could be a
    Type-J, in many cases i have seen 2 sets of these types
    wrapped around heating tubes.
    only 1 needs to be used, in any case they are very small conductors
    and mostly the J type which is 2 unlike metals twisted and electrically
    bonded together.
    the idea is when its heating one wire will contract more than the
    other causing tension forces which produce a small amount of current to
    the ratio of heat.
    with these types you need a HI-Z micro volt meter to see the voltage
    coming out of it.
    some 10Meg-Z DMM's have a low scale that will read it.
    under an ohm meter it will appear to be shorted.
    now the RTD types ( Resistor thermo device).
    that is basically a resistor that decreases in value
    as the temp goes up. these was have 2 wires
    then you have the IR (infra Red), where light is used to generate an
    effect with a IR detector since temp produces IR in most cases that i
    know of..
    those comes in a different variety.. , modular types which require a
    gnd, Vcc and 2 optional outputs.
    some times it just a simple IR diode with a lens which only have 2
    so take your pick..
    the Twisted Wire types normally use the same type of
    material as the lead wire to the controller.
  3. Thanks for the detailed explanation. I'm working with a Micrel MIC280 and it
    use a 2N3906 transistor junction as its remote sensor. Micrel has a demo
    board and software that runs off a PC's printer port and you can set "high"
    and "low" level trip points.

    I'm working on a USB temp controller with multi-zone sensor inputs based
    around the MIC280. Its been a fun project.
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