DAQmx Perform bridge Offset Nulling Calibration on task subset?

[adekruif]

I have several bridge channels that I am bringing in with a NI 9237 and I would like to perform the offset null calibration on some of the channels. I have successfully set up the system to do an offset null on ALL the channels, but I can't get it to work with a subset. I have tried setting up a Global channel in MAX (through creating a constant from the channels input to the null VI), but I get an error stating that the "specified channel is not in the task". 

I am currently using a simulated cDAQ 9139 chassis with two 9237 cards.

[Cy_Rybicki]

The DAQmx Perform Bridge Offset Nulling Calibration VI has a 'channels' input that you can use to accomplish this. You have left it unwired in your example which is why it is calibrating all of the channels in the task. 

[adekruif]

I tried wiring that by creating a constant off the input terminal. When I create that constant, it has me setup a global channel in MAX and then when it runs it says that the channel is not in the task.

I did figure out a way to do it, it's not pretty and requires the user to pay attention but it does work. 

[adekruif]

The "solution" I posted above only works if you want to balance consecutive bridges starting with the first channel. If you want to balance bridge 2, but not the first one it does not work. Still trying to figure out how to use the channel input for offset nulling. 

[adekruif · Accepted solution]

After doing a bunch more searching I stumbled across this thread: https://forums.ni.com/t5/LabVIEW/Reading-load-cells-and-strain-gauges-with-offset-nulling-using/td-p...

You can use a string as the input to the offset null channels and this way you can null only the channels listed.