Problem about read Sin wave data by DAQmx

[hanwei]

Hi all:

 I meet a strange problem about reading Sin wave data.

Now I am using a external functional generater to generate a Sin Wave, and I want to read it by DAQmx.  But the data (voltage) that I read is too strange, (seems like the data that I read from the Multimeter )and can't show conrrect Sin wave in Graph Display.

I don't know what's wrong about it, does it need a special configuration for AC voltage?  What is data that I read?  rms? or something else

Thanks a lot

[hanwei]

The configuration about it is attacthed here, I think it is normal.

Best regards

Message Edited by hanwei on 02-22-2008 12:10 PM

[Dennis_Knutson]

You've specified differential. Is that how you have physically connected the input to your board?

[hanwei]

Thanks for your replying

Actually, I am using PCI 6040E DAQ card, Scxi 1001 chasis, Scxi-1102 AI module and Scxi1300 terminal block. My connection line from functional generator is directly connected to the Scxi1300 terminal block. 

After I changed the "Terminal Configuration " from differential to <let NI DAQ choose>,  the test result is same.   (which configuration should I use?)

I am not sure what  the Data I am acquiring is ,   RMS ??

Message Edited by hanwei on 02-22-2008 01:20 PM

[pallen]

Hello Hanwei

Looks like your configuration is set for 100 samples at 1000 samples per second, continuous.

Depending on your signal, this may not be fast enough. Your card is capable of much faster acquisition rates. Try bumping it up to 10,000 or even 100,000 samples per second. The card is capable of 500kS/s

[hanwei]

Thanks

I try to change the sampling rates, but it is still not working,   by DAQ MAX,  the data I got is 0.19V, when I set a 4V 145hz, Sin wave Output in Functional generator.

It seems the DAQ read this data as DC voltage.  When I used other data measurement equipment , like oscilloscope,  it's fine.

I don't know what's going on about it?  something wrong of configuration ??

[Dennis_Knutson]

How exactly are you determining the voltage from the DAQmx task? Is this the max amplitude you see in a waveform dsiaply or are you doing something else?

[hanwei]

sorry, 0.19V is just a  example approximate value that I want to describe the problem, of course it is always changed

I didn't set any special configuration parameters in MAX, just default.

you mean, if I built the basic task with default parameters, the DAQ MAX should recognise any AC or DC voltage signals automatically. right?

Message Edited by hanwei on 02-22-2008 03:47 PM

[Dennis_Knutson]

I'm not at all familiar with the scxi equipment but the DAQ card is only dc coupled I believe. As far as the physical connections, again, I'm not sure how your scxi works. Instead of just saying that you have connected a signal source to the board, why don't you provide the details on what is wired where (include pin numbers, etc.).