Input analog signal with trig signal on DAQPad6020E

[brunet]

I would like to record an input analog signal in continous with trig signal on falling edge. The frequency trig is 3.87hz (258ms)with 5V level. In fact I want to record the input analog signal every 258ms.

I use a DAQPad6020E and the VIs "AI-Config", "AI-Start" and "AI-Read" with a "digital A" trigger type (PFI0/TRIG1 on block connectors) and record datas in a file.
I use the following configuration:
- sampling rate= 100000 S/s (max rate DAQPad6020E)
- minimum scan= 25200 pts
When I read the datas I notice that the gap between the first point of the first acquisition and the first point of the second acquisition is 1016ms and not 258ms like the trig.

I change the configuration:
- sampling rate= 10000 S/s
- minimum scan= 2520 pts
The gap is now 516ms (it correspond to two trig)
An other configuration:
- sampling rate= 155 S/s
- minimum scan= 40 pts
The gap is 516ms (it correspond to two trig)

I use also the VI "AI-Wave" but the results are the same.
I don't understand what happend. Maybe it's due to the card limits ?

Thank you for your answer.

[Isabelle]

Hello,

A trigger is an external stimulus that initiates one or more instrument functions. Trigger stimuli include a front panel button, an external input voltage pulse, or a bus trigger command. The trigger may also be derived from attributes of the actual signal to be acquired, such as the level and slope of the signal.

A trigger is not a clock.

If you want acquire with a specific clock, I advise you to use external clock. Instead of using your signal as trigger, use it as external clock.

Have a look at "Cont Acq & Graph Ext Scan Clk - D trig.vi" example. This example is provided with LabVIEW (Help >> Example Finder).

Here a tutorial about external clock acquisition :
http://zone.ni.com/devzone/conceptd.nsf/webmain/7d8eaea1d87cfb2686256802007b8c52?OpenDocument

Regards,

[brunet]

Thank your for your answer Isabelle.

But I'm not sure that the VI "Cont Acq & Graph Ext Scan Clk - D trig.vi" is appopriate.
I would like to acquire the input analog signal every 258ms (with my trigger) and with scan rate 10000 S/s for example.
I would like that each edge falling of my trigger initiate the acquisition.
Is it possible to take the scan of labview (10000 S/s for example) and external clock (my trig) to have every 258ms a measurement of my analog signal (with 2580 points)?

[Isabelle]

Hello,

If i understand you, you want to do finite acquisition every 258 ms.

The first example uses 2 devices (multifunction DAQ and counter/timer device):
http://venus.ni.com/stage/we/niepd_web_display.DISPLAY_EPD4?p_answer=&p_guid=BFE6E379D5807506E034080020E74861&p_node=201213&p_rank=&p_source=Internal&p_submitted=N

But you can program both devices in DAQmx, if you have NI-DAQ 7.3.

The second example only use the multifunction DAQ device.
http://venus.ni.com/stage/we/niepd_web_display.DISPLAY_EPD4?p_answer=&p_guid=B45EACE3F09F56A4E034080020E74861&p_node=DZ52335&p_rank=&p_source=Internal&p_submitted=N

Regards,

[brunet]

Merci pour votre aide, mais je n'arrive pas à accéder aux exemples que vous m'indiqués : impossible de se connecter aux adresses web !?

cordialement,

Christophe

[Peter D'Hoye]

FYI, DAQmx does not support the DAQPad6020E...


Peter

[Isabelle]

Bonjour,

Vous pouvez voir la page www.ni.com/examples.

Salutations,