Generating fast analogue ramps simultaneously

[GDBruce]

Using DAQ-mx, I am trying to output two fast and simultaneous analog ramps.  I have created the attached .vi and know that if I try to output just one ramp, my method works.  However, when I add the second ramp one channel outputs a ramp and when it is finished the other ramp is output on the second channel.  Can you spot my error?

[Mark_SAI]

Hello,

Could you post the waveforms2.vi for us to try?

Thanks

[GDBruce]

Here it is, Thanks

[Mark_SAI]

Hello,

I would suggest having a look at the Cont Gen Voltage Wfm-Int Clk VI. This VI is located in the Example Finder under Hardware Input and Output » DAQmx » Analog Generation.

Using a similar approach will give you something like the modified VI I have posted. I don't have any hardware to test this on so please let me know if it works or not!

[GDBruce]

Unfortunately, I'm using v8.5, so can't open your .vi.  Can you post a screenshot? Thanks again

[Mark_SAI]

Hello,

I have attached an 8.5 version, I hope it works.

[GDBruce]

No joy, I'm afraid.  The channels now both immediately switch to their initial values (which is an improvement on my effort), but then remain at that voltage.  Thanks again anyway

[Mark_SAI]

Hello,

Just a minor modification this time

[GDBruce]

Hello again. This now works nicely.  I'll possibly add another condition to stop the while loop after a certain time, as the loop does not seem to exit.  One issue I still have is the speed.  The ramp is nice and smooth on long timescales, but if I want to ramp in, e.g, 2ms it essentially becomes a double-step.  Is there anyway to smooth out the ramps on this sort of timescale (which is actually what I'm aiming to use)?  Thanks again

[Mark_SAI · Accepted solution]

Try increasing the rate constant to something appropriate for your hardware (i.e. within the maximum sample rate for your hardware). You could try 50000. You will also need to change the waveform generator sample speeds too (they are all set at 1000hz). Maybe make a front panel control and replace all the 1000 constants with a wire to the control.

 I hope this works!

Message Edited by macaba on 07-23-2009 09:10 AM