Cannot generate square wave with USB6251

[peterpeter5431]

I have a USB6251.  I am trying to generate a voltage.  I would like to use the DAQ assistant to do so.  The voltage I am trying to generate is like a square wave, only I am summing several square waves of different amplitudes and frequency so that it is not simply a logic on/off waveform.  I am able to generate sine waves over 20Hz.  Under this, the amplitude starts to decrease to less than requested.  When a square wave is requested, it generates a wave at the proper frequency but the voltage spikes and then decays exponentially periodically.

[Jordan F]

Hi peter,

Could you post a screenshot of the behavior you are seeing with the square and sine wave output?  Also, how are you creating and outputting your signals?  It sounds like you are using the Express VIs so I attached a quick piece of code that shows how to do this using the Create Analog Signal vi and the DAQ Assistant vi.  I was able to output a square and sine wave over 20Hz with no signal decay on the 6251.

Message Edited by Jordan F on 06-17-2009 07:49 AM

[wildcatherder]

As a former electronics technician, I'm guessing the problem was high capacitance either in the load or the measurement circuit.  That would result in the high-pass filtering effect described - just for future viewers.