Problem in producing dual channel analog output waveforms

[viswa]

Hi all,

              I am trying to generate two analog output waveforms synchronously. At the moment the VI is working properly. I am using Labview 8.2 and USB6221 DAQ board.

One of the analog output voltage drives a piezo vibrator at frequency say 2000 Hz, simultaneously another output generates 50mV at 2000Hz.

Now the problem is i want to drive piezo at different amplitude say 1,2,3, or5V etc.....i can genrate upto 2000Hz smooth waveforms but as i increase amplitude say from 1V to 3V DAQ card is unable to drive piezo at 3V it still shows 1V even though there is change in amplitude.

I have changed number of samlpes and sampling rate also but there is no effect on amplitude. 

Is there any relation between frequency of waveform and amplitude?????

Any help would be greatly appreciated.

Regards

visu

[Broken_Arrow]

So... is this a question about your VI or about the hardware (DAQ) ?

• Your VI has to be stopped and restarted when you change a setting, so be sure you're doing that, or rewrite it so it doesn't need to be started.
• When you say "it" still shows 1V, what is "it"? Are you looking at an oscilloscope? The VI? 

Message Edited by Broken Arrow on 09-25-2009 07:55 AM

[alpha1]

Hi Viswa,

There is no relation between frequency and amplitude, they are perpendicular to one another, so changing sampling rate will not affect the amplitude. The VI appears to be outputting correctly according to the waveform on the screen, I've just grabbed a DAQ to try and replicate the problem and will report back shortly.

[alpha1]

Hi Viswa,

I've tried to replicate the issue you seem to be having, but using the VI exactly as you have it seems to work as expected for me. For example, when I select an amplitude value of 3.00 in Waveform Information Channel 1, the actual output on ao0:1 is the same as the Output Waveform that is displayed, a sine wave with ±3 V peaks.

As Broken Arrow has pointed out, you are not able to change the amplitude while the program is running since the Waveform Information Channel 1 inputs are outside of your while loop. Please let us know if you're still having issues.

[viswa]

Hi all,

                 "It" refers oscilloscope. I can see that the DAQ board is producing waveforms as i instructed. When one of the outputs is connected to piezo vibrator then the DAQ output can not drive more than 3V at 2000Hz. 

Is this due to impedance mismatch?

[alpha1]

Hi,

It's possible that it's due to an impedance mismatch, what's the impedance of your piezo component? And what happens if you output at a lower rate? Do you get the same result?

[Broken_Arrow]

As the peizo nears saturation, its impedence drops, thus the loads becomes more difficult for the driver. However, 3V seems small. Check your peizo datasheet.