How to generate a square signal with 60hz-120hz frequency?

[ColombiaHM]

We are using labView 8.6 to create a square signal (60Hz) with Simulate Signal VI to control an external system. We are using a cDAQ9172 with a NI9265 module (analog current output) to get the physical signal.

With a digital oscilloscope the frequency measure of the output signal doesn't correspond with simulated signal.

How can obtain the same output frequency?

[Schneiater]

Hi ColombiaHM,

You should use the simulate signal connected to a DAQ Assistant (or use the low level functions).

The configuration of both should use a rate higher than the signal frequency you want to generate (for example 1000Hz). the number of samples should be the same at the simulate signal function and at the DAQ Assistant, for example 100.

This should work fine.

Please, if you are still having problems, detail your scenario and send us the code or some screenshots.

Regards,

[ColombiaHM]

Is not working. The scenario is like this. We are taking temperature signals with NI9211, we can see this signals in LabView, so this is working. Now we need to control the temperature measured, so we have to generate a square signal (120Hz), in Labview we are generating the square signal using Simulate Signal Block, so this signal is taking out using NI9265 (current output) to control the system. We can extract this signal using DAQ Assistant Block, but the freguency measure in the outside signal is not the same that we generate on the Simulate Signal Block, so the control is not working. What can we do to obtain the same frequency? Maybe is for sample rate in this blocks, but we have proved a lot of values and obtain the same result.

You can see the block diagram in next picture, so if u can help us just post a possible solution.

[Dennis_Knutson]

Why are you using 1 Sample On Demand? One sample means ONE SAMPLE - not a waveform.

Change to N Samples or Continuous Samples and make sure Use Waveform Timing is checked.

Edit - looking closer, don't understand at all the Select function. I have no idea what will happen when you wire the dynamic data to it but it just does not make any sense. And, no matter what, you will pass a single value to the DAQ Assistant. All that will do is generate a DC signal.

.

Message Edited by Dennis Knutson on 03-12-2010 12:39 PM

[Schneiater]

Now I think I understood your scenario.

Please take a look in the attached pictures and I think this can generate your square wave (in this example, I put 60Hz of frequency).

You can generate the signal with the Simulate Signal andthe DAQ assistant will only pass this signal to the DAQ board.

Please, let me know if this solve the problem.

Regards,