Data aquisition problem with PCI-6024E and external triggering

[Kristian Laß]

Hello,

I have a problem with data aquisition using LabVIEW 6 and an NI PCI-6024E
DAQ card.

I want to read two values from two analog channels on the rising edge of
an external trigger signal. For this purpose, I have connected my trigger signal to the STARTSCAN input pin und my two analog signals to the analog inputs No. 1 and 2 (Non-referenced single-ended).

My problem is that I can read the first channel and get reasonable values, but the values I get from the second channel don't depend on the actual signal connected to this input, but instead are somewhat correlated to the values from the first channel. It doesn't matter to the application what I connect to the second input channel - the
values I get don't depend on it.

I have enclosed a a small example VI using my data aquisition technique.

Does anyone of you have an idea of what's going on there?

I would appreciate your help very much.

Best regards
Kristian Lass

[Filipe A.]

Kristian;

I don't believe the problem you are seeing there is related to the external trigger connection, but to a too small interchannel delay in between channels.

If you don't give enough time to teh interchannel delay, the instrumentation amplifier might not have enough time to settle properly, so you will always see the signal that is connected to the previous channel on that channel, regardless what you have connected to the second channel.

The AI Config.vi has an input for you to change the interchannel delay of your acquisition.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[Kristian Laß]

Dear Filipe,

Thanks for your answer.

Unfortunately, it didn't resolve the problem. Even setting the interchannel delay to a such a large value as 1 s didn't fix the problem (although the program ran much more slowly, of course).

Best regards
Kristian Laß