Thermocouple board - Is there a way to know if a thermocouple is connected?

[macmack5]

Thermocouple board - Is there a way to know if a thermocouple is connected to a thermocouple? I have a project with panel mounted plugs (8 total) and it would be nice to have a way to know if there is a thermocouple plugged in? (Plugs are connected the hat)

 

[macmack5]

I should add that I am accessing the board from a Python source.

 

[alexburcea]

Hi,
There is no difference between disconnected thermocouple and one that measure the same temperature as the card, the voltage is zero for both situations.

 

[macmack5]

I have everything connected, good response, but the K type thermocouple readings show a significant offset from actual temperature, say 15 degrees F. I am using thermocouple wire from the jacks to the board. Jacks are K type. Polling the boards shows type 3 which should be correct. Any suggestions?

 

[alexburcea]

Do you connect the wires of the thermocouple directly on the screw connectors of the card? Did you know the card respond with degree Celsius temperature? (I guess you convert it in F)

 

[macmack5]

I have a through panel jack rated for K type, the thermocouples have male plugs. The jacks are wired to the board with thermocouple wire.

 

[alexburcea]

Ok, but we measure the temperature of the screw terminal connector but if the main connector is elsewhere the compensation is wrong.
Could you share the response of the "smtc 0 read <ch>". "smtc 0 readmv <ch>", "smtc 0 readct <ch>" for one channel <ch> that has thermocouple connected?

 

[macmack5]

In the mean time I wired straight in and it is basically correct.

 

[macmack5]

For the channel with the TC wired straight in:
smtc 0 read 1 24.1
smtc 0 readmv 1 -0.20
smtc 0 readct 1 29.6

for a channel through plugs:
smtc 0 read8 8.4
smtc 0 readmv 8 -0.66
smtc 0 readct 8 30.0

 

[macmack5]

wired in: 24.2 C
through plugs: 8.0 C

 

[alexburcea]

Is hard to find the right explanation but is look like introducing a new set of contacts acts as a new thermocouple..

 

[macmack5]

I believe you are correct. I will experiment with whether it is stable enough to use, or whether I have to run the wires straight to the board.

 

[macmack5]

ie, can I add a calibration equation over the range of interest....

 

[alexburcea]

The only calibration can be performed is for voltage measurement. If you wish to calculate yourself the temperature from voltage and connector temperature you can because you have access to both measurements.

 

[macmack5]

Further experimentation: If I use a commercially available 6 foot extension cable (comes with M/F plugs), remove the F plug, connect to the board, plug into TC on other end, I get good readings. But the panel plugs wired with commercially available type K cable gives the errors mentioned earlier.

 

[macmack5]

I then connected 10 M (30 ft) of TC wire to a TC and to the board - works. So apparently, the panel connection strip is the problem. (Just twisted TC extension wire and TC wire together. No screws, solder, etc.)

 

[alexburcea]

Thank you for doing those experiments and sharing the results.