5112 pci : Minimum Time between Trigger and Data Acquisition

[tdk]

Hi All,

I have a program to record the data of two superimposed sine waves (waveform not important) from a function generator with a 5112 PCI card.  Data acquisition is supposed to start at the trigger of the fuction generator.  The triggering works fine on the oscilliscope,  which I use to monitor what goes into the 5112.  However, when I look at the data I receive from the 5112 I notice that there is a delay between the trigger of the function generator and the time the 5112 starts to acquire data.  Does anyone know what the minimum time would be between the trigger and the data acquistion from the 5112.  The delay I am seeing is in the range of 10ns.  

One caveat is that my trigger is not TTL.  I am sending an arbitrary waveform pattern to my function generator and in this mode the trigger is not TTL, but rather a short pulse at the beginning of each waveform period.  However, even though the trigger is not TTL, it triggers correctly on a really old oscilliscope I have.  Also, when I make the trigger TTL there is still a delay albeit slightly smaller.  Any help is appreciated.

Cheers,
ScKaSx 

[Jordan F]

What are you currently doing for synchronization?  Are you using Tclk?   How are your triggers currently set up?  If you use Tclk in your system this will match up the triggers for your FGEN and Scope so they start aquiring at the same time.  Here is some more information about using Tclk. Also, I attached a link to an example program that synchronizes a FGEN with a Scope.

National Instruments T-Clock Technology for Timing and Synchronization of Modular Instruments

http://zone.ni.com/devzone/cda/tut/p/id/3675

NI-TCLK Synchronize AWG and High-Speed Digitizer

http://zone.ni.com/devzone/cda/epd/p/id/5029

You say that there is a delay from when the trigger occurs, is a trigger routed directly into the Scope or through the backplane of the chassis?  There will be a delay of at most 1 sample clock period before the digitizer will start aquiring.  This is because a sample is going to be taken on the edge of the sample clock and a trigger might occur right after an edge is seen.  However, if you are routing the trigger to the Scope with a longer cable length or through the backplane than I would recommend to use Tclk to synchronize the devices to start at the same time.