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Wiring thermocouple wire to read delta temperature

Discussion in 'Electronic Design' started by Mike in Arkansas, Aug 15, 2003.

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  1. I need to measure the inlet and outlet air temperature of an apparatus
    to find the Delta T or rise. Is there a method of wiring the (T type)
    thermocouples to read only the temperature rise? I've messed about
    with it for a while and done a google search and looked through my tc
    manual to no avail. Any help appreciated.
    Thanks, Mike
     
    Kamalakkannan likes this.
  2. Take a look a the following paper:
    http://cfa-www.harvard.edu/cfa/oir/MMT/www.mmto.org/MMTpapers/pdfs/ctm/ctm99
    -2.pdf

    The first page deals with delta temp measurement.

    Using Type T Thermocouples, wiring the Constantans together, and reading the
    signal between the two copper wires,
    has the advantage of eliminating the junction at the Terminal Block.

    Don Cleveland
     
    Kamalakkannan likes this.
  3. John Jardine

    John Jardine Guest

    Thermocouples are inherently differential.
    Could not just a *single* thermocouple be strung across the inlet and outlet
    measuring points?.
    regards
    john
     
  4. You need a junction at each measuring point. This is do-able with
    three pieces of wire. Doing it the way I suggested removes any errors
    from temperature differential between further junctions at the
    measuring device. Whether it's one Constantan wire or two closely
    similar ones spliced together makes no difference to the output, nor
    is the temperature at that "junction" of any great importance (though
    I'd not want it too different in case the alloys were not exactly
    matched). Making the junctions from three pieces of wire (with the
    copper taken from the same roll of wire) would yield the best
    accuracy. BTW, thermocouple only approximately measure difference in
    temperature, they are nonlinear and also the output is also dependent
    on the absolute temperatures.

    Best regards,
    Spehro Pefhany
     
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