04-25-2012 03:20 AM
I plan to use 4 chassis in a synchronous DAQ - 1x PXI and 3x cDAQ configured on individual-channel basis. Some of them reading Voltage (conditioned transducers) and some of them ACC (IEPE accelerometers). Before the main DAQ.VI I configure the 4 tasks (1 per chassis) and have tor ead starting offsets of all channels in use. This is the "Save Nulls.VI", having a button to allow a 60 sec settling ICP time before the acquisition sessions. The ACC channels are for now on the PXI chassis (PXI-4472 modules). Since the PXI chassis IS NEVER SWITCHED OFF I know that after the 1st acquisition all IEPE channels will remain ON forever.
So I need a VI to turn the IEPE currents every day before we leave. I have read of more solutions and decided for a Voltage dummy reading of a single sample of all channels. Attached is its diagram.
Is this a correct solution?
Thanks in advance,
04-26-2012 02:21 PM
I was taking a look at this article. One paragraph seemed particularly relevant:
"Enabling IEPE excitation closes a relay on the DSA device. Once turned on, either by using a microphone channel or by using a property node, IEPE excitation will stay on for that channel until explicitly turned off. The IEPE excitation will even persist after you clear your DAQmx task. To turn off the excitation, use a property node with an excitation value of 0."
I would try using the property node instead.
05-04-2012 12:40 AM
DAQmx doesn't program the hardware until you commit or start the task. Add a DAQmx Control Task VI with the input set to "Commit" between the property node and the DAQmx Clear Task VI.