update amplitude while running labview

[Jason_Chan]

Hi,

I am using PCI 6120, i am using a example code in labview 7.1 "Continuous Generate Voltage Waveform.vi". I am using a frequency of 1000 Hz and start running the program using amplitude 2 Volt. While running, I want to increase or decrease the amplitude voltage and this mean i also want the amplitude of the output waveform to change too. Please tell me how to do it. I do appreciate your help. Thank you.

Best wishes. Chan 

[devchander]

Hi Chan,

In this VI chosen form the set of examples shipped with LabVIEW,  you can change the generated waveform's parameters on the fly.

In menu, find : file->vi properties-> documentation,  to read the vi's documentation.

Regards

Dev

Message Edited by devchander on 01-24-2006 03:39 AM

[Jason_Chan]

Thanks Dev,

I have download the vi and try to run it. The amplitude of the output waveform still didn't change when i change the amplitude in the front panel. Can you please advise me what should i do. Thank you.

[devchander]

Hi Chan,

Ops, sorry!

This Vi with a small modification to the previously attached LabVIEW example will work.

Regards

Dev

Message Edited by devchander on 01-24-2006 04:15 AM

[Jason_Chan]

Hi Dev,

Thanks again for your reply. But, it still can't work. When i change the amplitude, only the amplitude of the Wave graph is changed but the amplitude of the output waveform didn't change. I check the amplitude of the output waveform using a Pico occilloscope. Please help me on this. Thank you again.

Best wishes. Chan

[devchander]

Hi Chan,

I have used this program for changing generated waveform's parameters (on the fly) with PXI 6713s and it has worked fine for me.

I have not run it on a PCI 6120 since i do not have that hardware.

So, I simulated a 6120 on my DAQ mx and ran this VI anticipating regeneration property related error.But no errors showed up.

Even in examples list, this Vi was displayed as being compatible with PCI 6120.

So, It beats me why you are not able to observe a varying output on the scope.

Hope others can catch any technical aspects that i might have missed out

lastly, It should not be a bother for you to check if the AO pinouts are correctly connected to the scope

Regards

Dev

[Jason_Chan]

Thanks Dev,

I have checked the connection, there is nothing wrong.  By the way, when i try to run the vi in BLOCK DIAGRAM. Error occur.

Maybe i cannot update the amplitude because of this error. I am trying to fix this error using Labview suggestion like increase the buffer sample or reduce the sampling rate.

Thank you.

Best wishes. Chan 

[Jason_Chan]

Hi Dev,

The error appear is ERROR 200290. Can you tell me what is this error. Thanks.

Best wishes. Chan

[Otis]

Hi Chan,

If you go to Help > Explain Error it will tell you why you are getting the error you are seeing:

Error -200290 occurred at an unidentified location

Possible reason(s):

The generation has stopped to prevent the regeneration of old samples. Your application was unable to write samples to the background buffer fast enough to prevent old samples from being regenerated.

To avoid this error, you can do any of the following:
1. Increase the size of the background buffer by configuring the buffer.
2. Increase the number of samples you write each time you invoke a write operation.
3. Write samples more often.
4. Reduce the sample rate.
5. Change the data transfer mechanism from interrupts to DMA if your device supports DMA.
6. Reduce the number of applications your computer is executing concurrently.

In addition, if you do not need to write every sample that is generated, you can configure the regeneration mode to allow regeneration, and then use the Position and Offset attributes to write the desired samples.

I would just follow the instructions as they are above.  You are probably just trying to generate the AO too quickly for the buffer to receive a new set of data.

If this doesn't help then let us know what is happening.

Regards,

[devchander]

Hi Rohit,

Also kindly post the values you have selected for the following paramaters

• Update rate/Sampleclock rate
• Buffer size

Regards

Dev

Message Edited by devchander on 01-24-2006 10:28 PM