How Can I Trigger and Synchronize NI PXI(e) DMM Cards Using Software?

Updated May 4, 2020

Reported In

Hardware

  • PXIe-4080
  • PXIe-4081
  • PXIe-4082

Software

  • LabVIEW

Driver

  • NI-DMM

Issue Details

  • How can I use a software trigger to synchronize two or more DMM cards?
  • I want to be able to synchronize DMM acquisition using software.
  • How can I synchronize DMM cards without any external hardware?
  • Do I need external hardware to send a trigger signal to the PXI(e) back plane?

Solution

There are two options available for triggering DMM cards with software. The first involves using a software trigger button, and the second involves using the back plane TTL line of the chassis. The details on how to implement these options are below.


Using a Single Software Signal For All DMM Cards:

One option involves using a software trigger to initiate the start of displaying data. However, this may consist of a slight delay between the cards due to the nature of software triggering. 
An example of this can be seen in the code snippet shown:

This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project. To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW diagram.


Using The Back Plane of The PXI(e) Chassis:

If the delay associated with the software trigger code is too large, another option is to use the "Configure Meas Complete Dest" VI. This can be used to send a trigger signal to a TTL line once the first DMM card has been successfully started.

More information on the "Configure Meas Complete Dest" VI can be found in niDMM Configure Meas Complete Dest and Generating a Measurement Complete Event.

The first DMM card will act as a master card that sends a trigger signal along the back plane of the PXI(e) chassis. The master card can be triggered via a software signal. Once the master card has been successfully started, the remaining slave DMM cards can be triggered.

Below is some example code that implements this functionality:


This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project. To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW diagram. 

The full code for each version has been attached.

Additional Information

Note: Some NI DMM cards, such as the PXIe-4080, can also be triggered using external hardware, such as an X-Series MIO device. 

The following are 2 additional VI's, attached at the bottom of this article:

The "SW Trigger Multiple DMM" VI

This code uses a Boolean button on the Front Panel as the software trigger. Once the Boolean has been registered as true by the Case Structure, the DMM data is displayed on the Waveform Charts.

The number of samples to acquire has been set to 100. When the software trigger is sent, a single data point will be added to each Waveform Chart. The chart will continue to be updated every time the "SW Trigger" button is pressed, until the total number of samples have been displayed.


The "DMM_Trigger_TTL" VI

This code uses a software trigger to trigger the first DMM card (acting as the master DMM). Once the software signal has been received, the master DMM outputs a signal indicating that the triggering signal was received. This is achieved by using the "Configure Meas Complete Dest" VI. The DMM Measurement Complete signal is then sent to one of the TTL lines on the PXI(e) chassis. The remaining DMM cards are then triggered from the TTL.