回复： Trigger DMM acquire

[daniel_vi]

Hi,

I am developing a platform to measure unit power consumption.  For hardware I have a PXI-1045 with 8106 controller and two DMM cards.  Right now I'm prototyping with two 4071's, but I'd eventually like to go with the cheaper 4065 DMMs.

For accurate power measurements, I'm trying to trigger the acquire (either waveform or multi-point), but I'm having difficulty setting this up.  How can I configure and use the sample clock from the 8106 as the trigger signal through the PXI backplane (TTL0, I think)?  Using the NI-DMM VIs it's easyt o set TTL0 as the trigger source, but I don't know how to route a clock signal to the TTL0 line.

Is this the right way to approach this problem, or do I need an external trigger source?  And if so, what could I use for this source?  I've also looked in to using the PXI Star line as a trigger, but I've gathered that this option would require another card to output a trigger signal...is this correct?

Thanks for all the help,

Daniel

[fond]

Daniel
Hi
I am also using PXI-1045 with 8106 controller developing a testing system.
For data aquisition hardware I have four PXI-6541 boards

are you familiar with PXI-6541,I know too little about it

have you got any example ViS on how to use PXI-6541 to generate and acquire data

thanks for all the help

fond

fondtothu@126.com

[ryannorthington]

fond,

The NI 6541 is programmed using the NI-HSDIO driver.  If you do not have this driver installed on your machine then you can find it here.

When the driver is installed it also installs shipping examples for HSDIO products. 

You can find them by using the example finder in LabVIEW (Help > Find Examples).

Once the example finder opens navigate to Hardware Input and Output > Modular Instruments > NI-HSDIO. 

Also, when posting about HSDIO please make sure to post to the correct board, this will help with the response time from the community.

I hope this helps!

[PBear]

Hi Daniel,

The 8106 is essentially a computer and thus doesn't have a clock source that drives any of the TTL/PFI lines. It controls the PXI communication and data transfer and contains the operating system. Since DMMs don't output triggers, only read triggers, you can not use them to send a trigger between each to start at the same time. To send a trigger over the TTL line, you'll need a third device (DAQ device, timing/synch card, counter board, etc.) that can write to these lines. The Star line must be controlled by a device that can drive this line. It's a trigger line that has equal traces to all slots from slot two.

If you are looking to start at approximately the same time, you can use the Send Software Trigger VI and configure them for software triggering. Please note that this is non-deterministic but if having a few milliseconds difference in start is ok then this should be fine. Also note that unlike our true digitizer boards, the DMM cannot PLL to a common clock or export their clock. This means that even if you start your DMMs at the same time (with a third device), there will be a small inherit difference in the sample clocks as they are not synchronized. Take a look at the following KnowledgeBases from some great information.

KB 398I9CR9: Routing an External Sample Clock to a PXI-407x DMM
http://digital.ni.com/public.nsf/allkb/F28F1E545EEC50D3862573D8006479FF?OpenDocument

KB 398I1ER9: PXI-407x DMM Synchronization Q&A
http://digital.ni.com/public.nsf/allkb/97C92B1770B3359E86256E90000044C0?OpenDocument

[daniel_vi]

Hi Patrick,

Thanks for the response.  Not exactly what I wanted to hear, since I was trying to avoid using the non-deterministic SW trigger, but a few ms may be acceptable.  For DC power measurements it is definitely fine, but I'm still a little worried about accurate AC power measurements.  Thanks also for the links.

Regards,

Daniel

[PBear]

Hi Daniel,

I'm sorry for the unfortunate news. While the two readings may appear phase shifted because they will start at different times, just remember exactly that: they started at different times. You can line the waveforms/readings back up in software so that the start times don't effect the correlation as much, though will not be as accurate as a hardware triggering and sharing a single clock. If you are interested in getting an external trigger solution (connecting a TTL signal to the front AUX connector), look at the following DevZone article. Also, on your behalf I have filed a product suggestion for our future DMMs to have more trigger abilities though a suggestion is not a guarantee of implementation. Thanks Daniel and have a great weekend.

Synchronizing Two DMMs with an External Trigger
http://sine.ni.com/devzone/cda/epd/p/id/3378


Message Edited by Patrick_B on 04-11-2008 08:36 AM