Assistance with Thermocouple/Data Logger circuit

Thread Starter

sday

Joined Aug 18, 2015
5
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.
 

mcgyvr

Joined Oct 15, 2009
5,394
Get another datalogger or buy a different temperature probe.. aka one that might output in the ranges accepted by your current analog inputs.
 

Thread Starter

sday

Joined Aug 18, 2015
5
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
 

mcgyvr

Joined Oct 15, 2009
5,394
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..
 

Thread Starter

sday

Joined Aug 18, 2015
5
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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