Autozero and the start trigger

[Zorchmaster]

When does the autozero operation occur relative to the start trigger?  I'm using a 6030E with an SCXI-1520/1125 and I have an external start trigger for the task but I'd like to use autozero to remove the offset from the channels (autozero once).  It *seems* like it is occurring prior to the start trigger but I want to make sure.  Also, how many samples does autozero use for averaging?  Does it take into account filter settling times when switching to the ground channel?

Thanks, -Bob

[Chad_A · Accepted solution]

For the autozero once case, the actual autozero acquisition does indeed occur before the start trigger.  Specifically, it occurs when the task moves to the "Reserved" state.  This happens automatically when you call the DAQmx Start vi, or you can explicitly force it to happen by calling DAQmx Control Task with the "action" parameter set to "reserve".

For the autozero acquisition, DAQmx tries to read 100 samples at 1KS/S (0.1 seconds of data).  If that's too fast for the specific task, then the driver acquires 1 second of data at the fastest legal rate. And yes, DAQmx does account for various filter settling times including the settling time to switch to the ground channel.