Analogue Hardware Trigger not triggering

[Alan D]

Hi,
I am having problems with an analogue trigger. I am using an E series PCI card which should ba able to do this. I have an encoder signal ( square wave ) and a pressure measurement. What I would like to do is take a pressure measurement at each rising edge of the square wave but what seems to happen is the VI takes a reading of the channel at the scan rate set in AI Start which is used to measure the trigger?!?!
Anybody know why this is happening? I have messed with the trigger level, hysteresis and type of slope but to no avail.
Thanks for your help and time,
Alan

[RIO-Todd]

It sounds like using an external scan clock would work better for you. Using an external trigger with an internal clock will start the acquisition on the trigger but will use the device's clock as the scan rate. You could use the external square wave as an external scan clock; this would acquire a measurement once every time the square wave pulses.

The LabVIEW shipping example Cont Acq&Graph ExtScanClk VI implements this. I've attached the LabVIEW 6.1 version of this VI to this message. You will be able to find this example by searching the LabVIEW shipping examples. You will need to connect the square wave to the STARTSCAN pin on your DAQ device. I hope this helps.

Regards,

Todd D.
Applications Engineer
National Instruments

[Alan D]

Thanks Todd.
Turns out that I had just tried that when I recieved your comment and the method works, thanks for your time and comments,
Alan