Type C thermocouple measurement and compesation with DAQmx

[El Zilcho]

Need to make type C thermocouple measurment using DAQmx. Analog thermocouple channel configuration VI has spot for custom scales in the units box but nowhere to wire the scale. Want to use cold junction compensation so is the only option to use a voltage input then subtract the cold junction voltage and then run that value through a conversion formula?

[George M.]

Hi,

To add a scale you have created, you will need to set up the UNITS to be "From Custom Scale". Then you will add a d DAQmx Channel Property Node. In that node is a property for Analog Input>>Custom Scale Name. Add the scale you created to this property, and you will be set up to use that scale. I hope this helps, and please let me know if you have further questions.

George

[El Zilcho]

That does not work. The program seems to already try and apply a scale since I get an error from start task that says the prescaled units are already Deg C, and the scale of course goes from volts to degrees. When I try to change the custom scale name after start task I get an error that says the units are invalid for this measurement type. So there seems to be some coding that won't allow you to replace the scale for a thermocouple measurement. I'll probably have to take voltage readings and apply the scale after I subtract the junction value which is unfortunate I have to do things that way.

[George M.]

Hi,

You are seeing this error becasue the task that you have defined is an Analog Input>>Thermocouple. To correct this, you should use an Analog Input>>Voltage, and then you will be able to define volts as your prescaled units. When you have a thermocouple task, it is expecting some type of degree measurment, which makes sense. Try this, and let me know if you have any further questions. Have a Great Day!

[El Zilcho]

Thanks, that is what I thought I would have to do; which doesn't take care of the cold junction compensation. I'll just do that in post processing.