PXI Digital Multimeter Synchronization

Issue Details

I am having trouble synchronizing two (or more) PXI-4070/4071/4072/4065 Digital Multimeter (DMM). Do you have any advice for accomplishing this?

Solution

There is an example program which shows how to configure two PXI-407x modules to start their acquisition when receiving the same external trigger. You can extend this programming method for more PXI-407x/4065 modules.

In this example, you need to provide a trigger for an PXI-407x device. To do so, you can use two different sources:

• Another PXI board (for example an X Series Multifunction DAQ board) that is able to route a trigger to one of the PXI Trigger Lines . You will need to configure all your PXI-407x modules to use that PXI Trigger Line as the source of the trigger.
• An external device that connects to each PXI-407x AUX connector using same length cables. You want to use cables that have the same length from the trigger source to the AUX connectors of each PXI-407x to reduce the trigger signal skew between modules.

Additional Information

Here are some answers about the most common questions:

Can an PXI-407x act as a master board that sources the trigger? 
No, it cannot. Notice in the example program that both PXI-407x modules are configured to receive a trigger, and none of them are configured to source it. This is because the PXI-407x board cannot route a start trigger to any line. You can configure the board to start acquiring when it receives a software trigger, but you cannot route this trigger to the PXI Trigger Lines or the AUX connector. Therefore, when synchronizing two or more PXI-407x boards you need to provide a trigger.

What is the maximum error I could see when synchronizing two PXI-407x boards? 
The trigger detection circuitry uses an onboard 28.8MHz timebase to clock the trigger input, so the maximum error you can have when synchronizing two PXI-407x modules is one sample. This method allows for the PXI-407x modules to start at the same time, but because both PXI-407x modules use their own onboard clock to acquire, there is no guarantee they are acquiring at the same time.

What should I keep in mind when using a PXI 18-slot chassis to synchronize 8 or more PXI-407x modules? 
If you are using a PXI-1045 chassis (or PXI-1006) and a PXI Trigger Line to send the trigger signal to the PXI-407x modules, keep in mind that the PXI Trigger Lines are interrupted every 6 slots. As a result, you have to route the PXI Trigger Lines from one slot to the next using the routing utility included in MAX 3.0 and later. Refer to KnowledgeBase 32GFMIWD for more information (see "Routing PXI Trigger Lines Across the Buses of Multisegment PXI Chassis" in the Related Links section).

Is it possible to link the timebase of my PXI-407x to the 10 MHz PXI backplane clock?
No. It is not possible to reference the internal timebase of a PXI-407x device to any external clock signal for synchronization purposes.