Missing triggers on 5122

[cirrusio]

Hello all,

I have a system consisting of 2 5122 PCI boards that I am trying to sync.  What I want to do is to use an edge trigger for the acquisition on one board and then use that same trigger to trigger acquisition on the other board.  I am exporting the trigger signal using a RTSI cable connecting the two boards (one I built myself using two 34 pin connectors and a standard ribbon cable; maybe this is the problem ).  This setup works just fine when I apply a wave with a frequency below 100 Hz; however, when I go above this frequency, the slave board seems to be consistently missing triggers.  It is not clear to me whether the signal is not being exported or whether the second board is just not catching them.  We need this to be able to operate as fast  as possible.  Does anyone have any suggestions? 

Peace, Matt

[Efrain_G]

Dear Matt,

There are many reasons why your RTSI cable could not be working at higher frequencies. One of those reasons could be a problem with impedance matching. You must also ensure that the length of your connector stays within the required specifications for a RTSI cable.

[cirrusio · Accepted solution]

Thanks, Efrain.  I was just about to post on this. (By the way, where are the RTSI "required specifications"?)

As it turns out, the problem was not the RTSI cable - works fine (was constructed using standard ribbon cable and 34-pin connectors).  Rather, the problem lay in the ordering.  I was arming the trigger on the slave card after I had begun acquisition on the master (duh!).  This meant that for signals with low center frequencies (such as 10 to 100 Hz), there was a good probability that the trigger would be armed before a signal was sent.  However, for signals running at higher rates, the trigger was often lost as it was being armed after the signal had been sent.  This was problematic because I was always checking to see if acquisition was complete on both cards before rearming and acquiring again.  I thought it was something simple like this, but somehow when I initially looked at it, I thought the logic was right.  C'est la vie.

Peace, Matt

[Efrain_G]

Hi Matt,

I am really glad that you figured what the problem was. I was looking around and unfortunately it looks like we don't quite have any RTSI scpecifications published. But mainly I was talking about the length of the cable.

[dansch]

Hi Matt,

Out of curiosity, are you manually sharing a clock or reference clock, and exporting the trigger to the slave from the master? I just wanted to see if you were using T-Clk to do this, since this is really the best way to accomplish what you need. It sounds like what you need could be accomplished by directly using one of our shipping examples, "niScope EX Multi-Device Generic Sync (TClk)" (or "niScope EX Multi-Device Configured Acquisition (TClk)" if you wanted it to run in a loop). Of course, this assumes you are using LabVIEW. Best of luck!

[cirrusio]

Thanks for the reply, Daniel.

I am not sharing a reference clock.  What is happening is that I have aperiodic events (particles traveling through a laser beam) that I want to capture the response on both cards for.  Acquisition is triggered when the voltage on the second channel of the master exceeds some set amount.  I think the example provided is probably not appropriate.

Cheers, Matt