How do I generate a signal from a PCI 5122 at triger start

[Joseph_Loo]

I am running Labview 8.2.1 on windows XP. I have a PCI 5122 high speed digitizer. I am trying to get a plus sent out on the PFI0 output of the device when the card is triggered. It seems that all I get is 4 volts from the device. I have set NiScope Export Signal wired in. This was an upgrade from Labview 7.1. I jncluded the block diagram of the signal generation.

I am pretty sure that the entire set of VI is oeprating, because I pipe the data retrieval into a graph to plot it. It periodically sends the signal and display it on the chart.

[Matthew_W]

Hi Joseph, 

niScope Export Signal is the correct VI to export the Start Trigger to PFI0. The PCI-5122 definetly supports this functionality, you can see that in the table below. This is from the NI High-Speed Digitizers Help file:
 

I did test this with a different digitizer, you can see the code below, I've highlighted the relevant part in a red box.
 
 

The example modified was niScope Multi Record.VI . I added the niScope Export Signal and set the signal to be exported as Start Trigger and the destination to be PFI0.

This should get you going! You mentioned a 4v level, is this what you saw on the PFI line?

Hope this helps! Have a great evening.

Best regards,

MatthewW
Applications Engineer
National Instruments

Message Edited by Matthew W on 09-20-2007 06:24 PM

[Joseph_Loo]

I am already doing that. It seems that the acquisition setup has to be done twice for it to work properly. I have to set the output value to pfi1 then to pfi0 before the output comes out. In addiition, the voltage coming out of the devis is about 3.34 volts.

There is another difference, I use the reset with the default value of True at the beginning of the acquisition cycle. Is it relevant?

[Joseph_Loo]

After further troubleshooting, we discovered that the part 189919-0R5 (this is the DIN connector for the trigger output is either mislableled, PCI 5122 is mis-wired, VI NI  export signal is not functioning right. It turns out when we set the value to PFI 1, it comes out of the label PFI 1.

[thomson]

On the 189919-0R5 cable, the center pin of the BNC labeled "PFI0" should connect to pin 9 on the DIN. "PFI 1" should connect to pin 6 on the DIN. (Also see the attachment). Are you saying these are reversed on the cable you have?

[Joseph_Loo]

That is what it look like. We just plug in the cable and use pfi 1 on the export signal. The signal comes out on pfi 0. Another item on the topic, is the Start Trigger suppose to appear immediately when the trigger occurs?

[Jennifer O]

Hi Joseph,

Do you have a multimeter available that you could use to check the continuity of your cable?  This would be my recommendation to verify the labling on your cable. Use the image that Thomson posted as a guide for the pins to probe.

The reset on the niScope Initialize VI will disconnect any routing that has been previously set up.  For example.  If you export your trigger to PFI0 and then without resetting (i.e. reset=false) run the application again while exporting the trigger to PFI1, the signal will actually export to both pins.  By resetting first (reset =true) the trigger will be disconnected from PFI0 and the signal will only export to PFI1 on the second execution.

Referring to the Triggering section of the specifications for your NI 5122 board, you will see the expected logic level for your PFI lines.  It is 3.3V CMOS logic when configured for output.  Therefore when you export the trigger you should see a 3.3V pulse on  the  PFI line you have chosen.

There is always a finite delay that results when routing a signal.  You can measure the delay by connecting the PFI line to one of your channels.  Depending on what you are interested in you can make this measurement in different ways.  This is easiest to do using the reference trigger since we can capture pre-trigger data.  You could route your reference trigger to one channel and the exported reference trigger (via PFI) to the other.  By reading pretrigger samples (I used 50%) you can see the distance between when the board is triggered and when the rising edge is measured.  I will attach a screenshot that I took on one of my digitizers.  The yellow line is the reference trigger and the exported pulse is in blue.  You could reduce the delay by minimizing the length of cable.


Hope this helps,

Jennifer O.

Message Edited by Jennifer O on 09-24-2007 01:15 PM

[Joseph_Loo]

The cable is defiitely miswired. pfi 1 is connected to pin 9 and pfi 0 to pin 6.

We also seem to have a problem when the signal is triggered. According to my engineer, the signal is appearing 2 - 3 miliseconds after trigger. It is my understanding, that the signal shoul appear within a micro second or so when a trigger condition occurs.

[Joseph_Loo]

There is another thing I noticed. I have the export signal before the trigger definition. is it required to be after?

[Matthew_W]

 
 Hi Joseph,

 The trigger delay for the Start Trigger is a software timed output event, as opposed to the Reference Trigger output which is hardware timed. You can see this in the screenshot posted by Jennifer O., there is a delay of ~250nS from Reference Trigger to output pulse. You could set the reference trigger position to 0% and achieve the result you are looking for.
Here is a description of reference trigger position from our website.

 The Export Signal does not have to be after the Trigger definition, it must be before the Initiate Acquisition vi.

 Please do post back if your still having problems with this application.

Best regards,

MatthewW
Applications Engineer
National Instruments

 

Message Edited by Matthew W on 09-24-2007 06:32 PM

Message Edited by Matthew W on 09-24-2007 06:33 PM