Hi Akellas
I have found another entry in the forum dealing with the same problem that I thought could be useful for you. It is located at http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=5065000000080000002A4D0000&ECategory=LabVIEW.LabVIEW+General . For your convenience, I have added the text below:
"We wrote a VI for acquiring data on legacy DAQCards that do not support
hardware triggering, e.g., DAQCard 700. We are are using LabVIEW 6.1.
The trigger signal is a square wave output that is routed into channel 0
(Ach0) which also starts the timing of an analog waveform which is routed to
channel 1 (Ach1). We are using software triggering and a rising slope. The
signal is about 25 ms in duration, and we are using an 80 kHz acquisition
rate.
The problem is that there appears to be uncertainty in the triggering (+-)
0.5 ms about 10% of the time which causes the signal to jump back. We still
pick up jitter but it is tolerable although we would like to eliminate it,
which is about (+-) 0.02 ms.
Is there away to minimize this jitter, such as increasing the size of the
buffer? We tried increasing the buffer size, but that did not appear to
help. I don't think the problem is that noise is causing pre-mature
trigger, but I'm concerned that there may be variable computational delays
between detecting the trigger and collecting the signal waveform. We are not
collecting any pre-scan points."
The answer was:
"Since you are using Conditional Retrieval trigger on your DAQ task, the analog trigger level will be computed by the NI-DAQ driver. Since that is not a hardware operation, you can expect some jittering due to that method.
The only way to eliminate that is by using a DAQ board that has Analog Trigger circuitry, so you can perform that opeartion in hardware."
Hope this solves your problem. But just as it is said above, we have board that have that functionality built in.
Regards,
Serges Lemo
Application Engineer
