Thermocouple with LJTIA | LabJack
 

Thermocouple with LJTIA

4 posts / 0 new
Last post
manuel aiello
manuel aiello's picture
Thermocouple with LJTIA

Hi, i have a T7 from which i'm streaming data at a scan rate of 1kHz from 3 channels (one for a load cell connected to a LJTIA, one for a pressure transducer and one for a thermocouple in differential mode, so i suppose there are 4 channels total) receiving chunks of 500 scan per read. But because of the high scan rate and number of channels i cannot have the correct gain (i use a range of +-1V) for the thermocouple and i get "scan overleap" error if i try to rise it.

So i was thinking of using the other channel on the LJTIA to read the thermocouple and use as coldjunction compensation the temperature of air calculated reading the temperature sensor on AIN14. 

What i wanted to understand if i can then use the LJM_TCVoltToTemp.vi to then calculate the temperature from the scans i get by converting the output reading of the thermocouple in millivolts knowing gain (201) and offset (0.4V).

Is this a good way to do it or i'm i missing a more direct and better procedure?

thank you.

EDIT

Moreover i was trying to read AIN14  (i didn't set range or resolution for it in the streaming) and i get a consistent value of 1.009772V, so according to the math in the datasheet should corrispond to CJC_T = V*(-92.6) + 467.6 = 374.095 K , but in Kipling i read a CJC_T of about 297.127 K  which to me seems fairly accurate.

Any suggestion on why?

LabJack Support
LabJack Support's picture
Using the Tick-InAmp for the

Using the Tick-InAmp for the thermocouple amplification seems reasonable to achieve higher stream rates. Note that the TCVoltsToTemp function is also available in LJStreamM using the scaling equation section.

I am not sure about the bad AIN14 reading. It could indicate some issue in your software, or perhaps some hardware issue. Do you see the same readings if you stream using our LJStreamM application? Does it make a difference if you stream AIN14 by itself or with your other channels?

manuel aiello
manuel aiello's picture
Do you mean that

Do you mean that TCVoltsToTemp function is available as a subVI or that is directly usable in LJStreamM? 

 

For the AIN14 i tried again and i'm now getting 1.855 V (295.827K) that i think is acceptable, so it was my fault.

LabJack Support
LabJack Support's picture
The TCVoltsToTemp function is

The TCVoltsToTemp function is available as a subVI, and it is exposed in the LJStreamM application through the scaling equations section:

https://labjack.com/support/software/applications/ud-series/ljlogud/ljlo...