622x PXI star trigger generation

[Wortel]

Hey all,

I was wondering if it is possible to use a PXI 622x card to trigger 3 PXI-4071 DMM cards using the PXI star trigger function.

We currently have a 1042 Chassis, a 8106 controller and 3 4071 DMM cards. I shall be using LabVIEW 8.5 and initially running in XP. The problem I have is that the 4071 cards cannot generate the trigger themselves (a fact the NI sales rep neglected to tell us) so we are now forced to purchase a card that is capable of generating the trigger to start the DMM cards sampling. The reason for choosing the 622x card is entirely financial...!!!

The equipment shall be used to measure 3 phase voltage/current during testing of large electrical generators (in a Sudden Short Circuit Test, to be specific), hence the need to synchronise the samples. Ideally I would like, at first, to start the sampling simply by pressing a button on the LabVIEW window that will tell the 622x card to send the trigger. When this is proven to work (after 10-15 generators have been tested) I would then like to change the program so that an event (monitored by the 622x card) will trigger the 3 DMM cards.

I shall be taking 10K samples per second for 15 seconds from each of the 3 DMM cards and storing them in an array. No calculations will be taking place during the actual data acquisition stage. All I need is the 3 1D arrays of the 150,000 samples. No time stamps are required.

Thanks in advance for any response,

Darren Mather.

[KvZ]

Hi Darren,

I'm sorry to here you where mis informed. As for your current question it is not possible to drive the PXI Star trigger bus from a M series device, Bellow you can find a link to more information regarding PXI Star trigger compatible devices

PXI Devices That Can Send and Receive Star Triggers

However the M Serie devices are able to sent out a trigger on one of the PXI Trigger lines. The basic setup that I would suggest is the following:

1. Generate a pulse train using a counter on the PXI-622x.
2. Connect the counter output to a PXI Trigger line <x>
3. Setup the DMM's to recieve a start trigger from this trigger line. (In the NI-DMM this line is called TTL<x> )

You can use the LabVIEW Example Finder to find the following NI-DAQmx example: Gen Dig Pulse Train-Finite-Retriggerable.vi This example generates a series of pulses each time it gets a external trigger. The Gen Dig Pulse Train-Finite.vi Example just generates a series of pulses when you run it.

The following example shows how to setup two DMMs to recieve the same external trigger. I think this is a good example to start from.

Synchronizing Two DMMs with an External Trigger

Hope this helps

Thanks

Karsten

NI Netherlands

Message Edited by KvZ on 03-14-2008 09:41 AM

Message Edited by KvZ on 03-14-2008 09:41 AM

[Wortel]

Karsten,

Thank you for your reply and the tips. I have looked through the list of cards capable of generating the star trigger and found the PXI-665x range of interest.

I would just like to confirm that this card is capable of synchronising the 3 PXI-4071 DMM cards in the PXI box and also capable of synchronising another PXI chassis, for possible future expansion?

My plan is to use the 6651 card to synchronise the 3 DMM cards using the star trigger when the program first loads and then to use a TTL trigger to begin the actual data logging, is this possible? I assume if I just sync the cards at the start and then use a simple button (or an event) to begin actually storing the data that there is no guarentee I will start logging from all cards at the same time?

I aim to monitor the signal from the 3 DMM cards in LabVIEW (without storing the data) untill an event occurs, then send the TTL trigger (or can I use the star trigger again?) from the 6651 card when an even occurs. The event will be a sudden rise in current over a specified time duration. The reason for sync'ing the cards at the start is that the signal is visually monitored (but not stored) on a display as a waveform while other tests are being carried out.

I hope that made some kind of sense, It's a very simple test but has a lot of critera that must be met in order to meet the required standards.

Thanks again for your help,

Darren.

Message Edited by Wortel on 03-14-2008 05:59 AM

[KvZ]

Hi Darren

I think this should be possible to do but there are a couple of issues with this that you need to consider.

First the 6651 is more of a slave board and is only capable of routing external signals, it does not have a DDS to generate any clock signals. You would normally use this in the Slave Chassis in a multi chassis setup. You would need a 6652 or 6653 to generate any clock signal and route this to the PXI Star trigger bus. For more detail for these board see the NI-665x User Manual.

If you are using a 6652 or 6653 then yes you would be able to generate a 'clock' signal that is exported on the PXI Star trigger and used by the DMMs as the start trigger for the acquisition. As for the event to trigger the data logging you would need to implement this in you monitoring code. When you detect the raise in current then you just start storing the incoming sample to disk. All you need to do is setup the DMMs, start the clock, start reading samples and feed them to your processing code which will decide when to start storing the data.

It is not possible to use a hardware trigger to start the data logging. But because all measurements are triggered from the same source you only need to keep the number of samples you read in sync and then you are sure that the data your are reading and storing is synchronized.

Hope this helps

Thanks,

Karsten
NI Netherlands

[Wortel]

Karsten,

Thanks for that info, just after I posted my reply I thought that I would just need to start logging the data after the event as it would be in sync from the start... It's been a long week...!! 😉

I'll make the recommendation to purchase the card (probably the 6652) and then shall re-post if I have any problems!

Thanks for the assistance and have a good weekend,

Darren.