Error -50150 when calling DAQmx Perform Bridge Offset Nulling Calibration.vi

[TobyD]

I am having an issue very similar to This One, but just the opposite is happening. I create a task that contains 2 analog input (quarter-bridge strain gage) channels. One of the channels is on an NI 9235 cDAQ Module, the other is on an NI 9219 cDAQ module. Both modules are in the same NI cDAQ-9172 chassis. When I try to run the DAQmx Perform Bridge Offset Nulling Calibration.vi on the task I get error -50150.

If my task contains channels from only one of the cDAQ modules the calibration completes successfully. Any ideas? I can't figure out what is causing this.

Other info...

LabVIEW 8.6.1

DAQmx 9.0.2

Toby

Certified LabVIEW Architect

[Brad_K · Accepted solution]

Hi TobyD,

This seems to be a variation on the other problem that you linked, CAR #4HDABJ0O in the legacy CAR DB, a.k.a. CAR #198928 in the new CAR DB.

DAQmx has special code for NI 9219 offset nulling, in order to handle the NI 9219's special quarter bridge scaling. (NI-DAQmx Device Considerations >> Physical Channels >> C Series in the DAQmx Help explains how quarter bridge mode on the NI 9219 is special.) It sounds like this is causing the NI 9219 offset null calibration to acquire data separately from the NI 9235 offset null calibration, leading DAQmx to disable all of the channels on one of the modules, which DAQmx handles incorrectly, causing the error.

It looks like CAR #198928 should be fixed in the next version of DAQmx. Until then, the workaround is to create separate tasks for performing offset null calibration on each module. Note that you can query the AI.Bridge.InitialVoltage property from each channel in these separate tasks, then set it on each channel in a combined task, so that you can perform your actual acquisition using the combined task. You only need separate tasks for the actual offset null calibration.

 

Brad

[TobyD]

Thanks Brad! Excellent description - I'll see about implementing the workaround.

-Toby