how to trigger an Interval triggered acquisition (PXI DMM)

[mstlaurent]

HI,

I have a PXI-4071 DMM and I am acquiring voltage at 100 Hz using the Interval triggering.  I also want the acquisition to start only when the Star Trigger line is activated from a FPGA board. I will then fetch the data continuously.

The timing for the start of the acquisition does not have to be very precise. 

I don't use a real-time controller, only a PC with a MXI interface. 

Is there a way to do this? 

I am currently using the Trig1 line to trigger a DAQ card in the PXI chassis but I could also modify the FPGA code if required.

Thanks! 

[EEsRULEtheWORLD]

Hi, mstlaurent.

What FPGA board are you using?  Some of our FPGA boards are unable to access the Star trigger line.

If your FPGA board is able to access the Star trigger line, you should have no issues configuring a DMM Trigger with the PXI Star as the trigger source.  To connect the 100 Hz signal to the 4071, a good reference is the DMM Help.  Here is a screenshot of how to connect a waveform voltage to this device:

 Are you planning to trigger aquisition of the DAQ card with the Star Trigger line, as well?  What DAQ card are you using?

[mstlaurent]

Hi,

We are using the PXI-7842R.

We are using the Star trigger to start the acquisition on a PXI-6259 without any problems.

I am using the DMM with the 'Interval' triggering mode to perform a continuous acquisition at 100 Hz. It works well but to my knowledge, you can use only one trigger mode at a time.

My question is: how can I synchronise the start of the acquision and still keep the trig mode to Interval?

If I change to the trig mode to Star Trigger, I could synchronise the start of the acquisition but how could I insure that the DMM samples precisely at 100 Hz? 

In other words, I need to trigger the acquisition on the Star trigger and I also need the DMM to sample at 100 Hz, which is done using the 'Interval' mode.

In all the examples I looked at, you have to choose only one trig mode. 

Thanks! 

[EEsRULEtheWORLD]

Hi, mstlaurent.

I checked with the team that supports our FPGA cards, and verified that the R series does support access to the Star Trigger line.  I have modified and tested the Acq Multiple Samples - Interval Sample Trig.vi example to include a start trigger that uses PXI Star, as shown:

The Interval Trigger will acquire measurements with a delay between each sample.  This delay is derived from the internal timebase.  The start trigger source is configured by the niDMM Configure Trigger VI.  In the above screenshot, the acquisition will start when a trigger is received at PXI Star and continue at a defined Sample Interval until the Sample Count is reached.

Let me know if you need any more information.