PXI DMM Synchronization

[ejensen]

I have 2 NI PXI-4071 DMMs installed in a NI PXI-1045 chassis. I need to trigger them to both read at the same time. My current implementation uses the software trigger, but it is not as precise as I would like. I have looked at all the NI provided DMM examples and spent several hours reading about synchronization with the PXI backplane, but I am having trouble making sense of it. I feel like I should be able to generate a digital pulse train and have the DMMs trigger based on the pulse train. There may be other methods which I haven't considered. What would be the best method for accomplishing this? Is there an example somewhere I may have missed? Thanks.

[LAVA 1.0 Content]

I have no experience with DMMs, but do you use Daqmx functions to read them out?

If so you can use the DAQmx triggering function.

One task could start at the same time the other start. Daqmx will set up the backplane lines as needed.

Ton

[ejensen]

The DMMs have their own VIs for triggering as far as I can tell. The best example I've found is '\examples\instr\niDMM\Triggers\Cont Acq Multiple Samples - Ext Trig - Ext SampleTrig.vi', although w/o DMMs, I assume the examples won't be available. 'niDMM Configure Trigger.vi' has an input for trigger source. It contains, among other things, TTL0 through TTL7. I can run the example with a TTL source selected and the VI sits and waits for a trigger that never comes. Any idea how I can generate a pulse train for these TTL sources? Would this be where DAQ-mx comes in?

[jdunham]

QUOTE (ejensen @ Mar 19 2009, 08:21 AM)

The DMMs have their own VIs for triggering as far as I can tell. The best example I've found is '\examples\instr\niDMM\Triggers\Cont Acq Multiple Samples - Ext Trig - Ext SampleTrig.vi', although w/o DMMs, I assume the examples won't be available. 'niDMM Configure Trigger.vi' has an input for trigger source. It contains, among other things, TTL0 through TTL7. I can run the example with a TTL source selected and the VI sits and waits for a trigger that never comes. Any idea how I can generate a pulse train for these TTL sources? Would this be where DAQ-mx comes in?

Did you ask NI tech support? It's reasonable to ask here, but for this kind of question (how do I use the advanced features of hardware product X) you will often get the best information from NI support. Not always, since sometimes forum users have worked through a given problem already, but usually.

[texasaggie97]

QUOTE (ejensen @ Mar 19 2009, 09:25 AM)

I have 2 NI PXI-4071 DMMs installed in a NI PXI-1045 chassis. I need to trigger them to both read at the same time. My current implementation uses the software trigger, but it is not as precise as I would like. I have looked at all the NI provided DMM examples and spent several hours reading about synchronization with the PXI backplane, but I am having trouble making sense of it. Most of the triggering info I've found is related to DAQ-mx, and I'm not able to see how I can adapt this for use with DMMs. I feel like I should be able to generate a digital pulse train, send it to the PXI backplane, and have the DMMs trigger based on the pulse train. There may be other methods which I haven't considered. What would be the best method for accomplishing this? Is there an example somewhere I may have missed? Thanks.

You will need additional hardware in order to synchronize your two DMMs. The DMMs cannot generate a pulse you would need in order to do this. If it is another PXI device (CTR/Timer or MIO, etc.) you can route the pulses onto the backplane in which case the Trigger Source would be TTL0 - TTL7. If it is not a PXI device, you can use the front connector for the Trigger Source. I don't have NI-DMM installed but I believe the front connector terminal would be something like TrigIn.

If you are doing multipoint and want ALL points to be triggered, you will also need to set the Sample Trigger Source to the same terminal.

If you have any other questions, I can try to answer them.

Good luck,

Mark

Ex NI-DMM Software Developer

[ejensen]

I have other hardware including NI PXI-6229. I have made some progress by modifying this and using PXI1SlotX/PXI_Trig7 as the destination terminal. I initially failed to understand that TTL7 was PXI_Trig7. I am now able to trigger a single measurement from the backplane. Adding a second should be easy enough. Thanks to everyone for the suggestions.