Assistance with Thermocouple/Data Logger circuit

Discussion in 'The Projects Forum' started by sday, Aug 18, 2015.

  1. sday

    Thread Starter New Member

    Aug 18, 2015
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    Hi,

    I want to take temperature measurements using a thermocouple and a data logger with analogue inputs, but I'm unsure whether it can be done with the set up I have. I have a 12 bit data logger that measures internal temp, pressure, etc. along with the following external ports;
    1. 4 x analogue inputs (0-20mA, 0-3v, 0-10v, 0-24v)
    2. GND
    3. 3V supply
    Is it possible to connect a k-type thermocouple to the 0-3v and GND ports and measure the voltage drop over the thermocouple. All information I can find uses data loggers with +ve and -ve channel inputs which I don't have so can the GND act as a -ve terminal?

    I believe the resolution using the 0-3v port would be roughly 7uV, which would be around 5C change in temp, but when I connect it up and take readings I get no registered potential drop (I should at least get some increase/decrease in values shouldn't I). Does my data logger require greater sensitivity or should i just use another data logger? i don't have an electronics background so not really familiar with how this works.

    Thanks for the help.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    969
    Get another datalogger or buy a different temperature probe.. aka one that might output in the ranges accepted by your current analog inputs.
     
  3. sday

    Thread Starter New Member

    Aug 18, 2015
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    Thanks mcgyvr, I did think that was probably going to be the outcome.

    I have tried looking at different temp probes but rtds require a current source and thermistors would require additional circuitry to measure their resistance too would they not? Therefore I think a purpose built thermocouple data logger would be best.

    Just out of interest on my data logger do the positive analogue ports measure potential relative to the gnd or am I wrong in connecting components in that way?

    Appreciate the help
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    You didn't post the model of your datalogger but yes they would probably measure voltage in relation to ground.. but if they have 2 inputs per channel (- and +) then it may be floating and the neg may not be tied to ground for isolation.

    What are you measuring/what accuracy/min&max expected temps?
    We could possibly suggest a probe with more information..
     
  5. sday

    Thread Starter New Member

    Aug 18, 2015
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    0
    I have an msr 165.
    I'm just measuring long term temperature changes between a range of 0 to 300 degrees c. Accuracy of 1 or 2 degrees.

    Thanks for the help
     
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