how do I setup pretriggering for a data capture

[weatherhound]

I want to capture data on three channels (simultaneously) using a PCI 4472 dynamic signal analyzer and want to capture this data when channel one reaches a certain level (trigger). I need to capture pretrigger data. How to do this?

[Claudia]

Hello,

The PCI-4472 uses the DAQ-STC chip, as E series boards do. You can configure the 4472 to use an analog trigger to start acquring data, and to take pretrigger samples the same way that you configure an E series board using Traditional NI-DAQ calls (DAQmx also supports E series board).

From your previous entries in the Developer Zone, it seems you usually program your applications in LabVIEW. LabVIEW ships with an example program that does exactly what you want to do. This example program is called "Acquire N Scans Analog Hardware Trigger.vi". In my PC, it is part of the library "anlogin.llb" saved in the folder "C:\Program Files\National Instruments\LabVIEW 7.0\examples\DAQ\anlogin". You can use any of your channels as the source of the trigger (see
the Analog Trigger specifications in Appendix A of the NI 4472 User Manual).

The acquisition will be simultaneous if you specify that you want to acquire data from 3 channels (or more) as soon as the trigger is received. All A/D converters in the 4472 boards are running at the same pace by design.

Hope that example works for you,

Claudia Lorente
Applications Engineer
National Instruments
http://www.ni.com/ask

[weatherhound]

thankyou very much Claudia, the example worked well for me and was exactly what I was looking for. I was trying to use the lower level AI VIs and wasn't having much success. thanks,
Jim