Using USB 4431 to Generate Analog output Waveform

[Anil_Reddy]

Hi Everyone,

I am really jumping between hardware for analog output.

I started with Measurement DAQ card, but the plan changed then.

Then i did using PCI 6221 successfully.

Now am trying to do with USB 4431. But the problem with this card is, it has fixed update rates. This is really challenging me on generating a waveform of some specific frequency. am generating a 21 point Sine waveform and then giving it to Analog Out on this card. When i mention 10000 as update rate and i give 100 hz signal, am getting a signal with around 475Hz on the output.

Any guess on where am going wrong.

Thanks in advance

Anil Punnam

[Anil_Reddy]

...............I could solve the issue....am generating a higer point (sampling rate of waveform and no.of samples in a block) waveform equivalent to some fixed output rate and am limiting the maximum output frequency to some point. with this i could solve the issue......

[Margaret F.]

Hello Anil,

Thank you for posting to the NI Forums! My suspicion is that you are using 10000Hz and the card is coercing that to the nearest update rate that it can handle. If you take a look at the Analog Out section of the 4431 manual, you will see  the update rates that are available. Check this out and let me know what you think. Have a good weekend!

Message Edited by Margaret F. on 04-24-2009 03:39 PM

[Anil_Reddy]

Hi,

i did not know about the fixed output rates. When i started working on that. i got an error about the update rate. Then i checked the manual and got to know about fixed update rates.

Is there any reason for desiging with some fixed update rates?

I could work with the card with some changes in the software. 

Anil

[Margaret F.]

Hi Anil,

The reason for the fixed update rates is because DSA cards have a much lower master timebase than regular DAQ cards. Therefore, the timebase cannot be divided down into as many increments as a DAQ card; however, as you know with DSA cards, the resolution is greatly increased. Hope this helps!