PXI-4220 does not maintain null and pot settings are not readable.

[bradh]

I have a PXI-4220 that I am using with load cells. 

1) When I use the "Daqmx Perform Bridge Offset and Nulling" it does null the channel.  But when I stop the currrently running VI and restart it, the channel again has the same starting bias.  Is this normal behavior?  Why do the pot setting revert?

2) Also when I read the pot setting using a property node - they do not seem to change, even though the bias does null.

Driver problem?

[Brad_K]

Hi bradh,

DAQmx channel and task settings don't automatically persist when you stop/restart your application. Stopping the application destroys the DAQmx task that contains your settings. Restarting your application creates a new DAQmx task instance with the default initial voltage and bridge balance pot settings, not the settings from the old task.

However, you can explicitly save a task to MAX using DAQmx Save Task.vi (from the DAQmx Advanced >> System Setup >> DAQmx Storage palette sub-menu). This is how the DAQ Assistant saves tasks. You can load a saved task by passing the task name to the task to copy parameter of DAQmx Create Task.vi, or by wiring the task name to the task input of any DAQmx VI. You can also save/load individual channels in a similar manner.

When you read the pot settings using a property node, are you reading the settings from the same DAQmx task instance that you calibrated? That should work. If it isn't, please post more information about what you're doing (such as a code snippet). If it's a different DAQmx task instance, then it will read the default settings.

Brad