USB 6009 some problems with loop controlled waveform generation

[Johnie]

Hello friends,

 I just experiment with new usb 6009 data aquisition card and have some problems with voltge waveform generation. I use analog output AO and write 1 sample to the card in each for loop execution. Everything looks fine when loop execution is software controlled but when I attempt to set any delay in loop execution the output waveform looks terribly bad and it looks as if there wasn't a sample&hold circuit( or zero order hold) on each output channel. The output signal ( i try to generate a sine wave and any arbitrary waveform that was stored on PC's hard drive before) looks like "comb" then, first when a new sample is written to the card there is a sherr edge like a sample-shoot and later  output voltage falls down a bit slowly, and when the next sample is written the same situation occurs. The longer delay is set the worse signal distortion occurs.

 The second problem is amplitude because when I try to generate sine wave of 5 V peak to peak  I recive wave of about 400 mv peak to peak.I don't belive that this problem is caused by not perfect connections to the ossciloscope and by some external noise.

I realy want to meet Your opinion. Is there any solution for my problem.What about time controlled generation and zero order hold circuits on analog outputs.Is there anything like that?

Any help would be appreciated

Many regards

 Johnie

[Ryan_V[DE]]

Johnie,

The USB-6008/9 should maintain an output voltage until the DAC is updated with a new one. It sounds like your "comb" is an effect created by AC coupling on your oscilloscope. That is, because you are updating slowly, any charge you accumulated when setting a new voltage will eventually discharge and you will return to 0V. The rate of this is dependant on your 'scope's bandwidth. Try changing the input to "DC Coupled." As for your voltage offset problem, it sounds like you are using a 10x probe and not accounting for it. Either tell your 'scope that you are using a 10x probe, or instead use simple clip leads. Please let us know if you have any additional questions.

Hope this helps,