Multifunction DAQ

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I am using the AO channels of a PCI-6024 DAQ board to drive

motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?I am using the AO single point vi in LabVIEW 5.x to generate the channel outputs.
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motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?How are you interfacing to the DAC card (a screw terminal device, the BNC-2090)? Also, have you tried just looking at the DAC outputs with a voltmeter to verify that they are changing correctly with the value you expect to see?

Mark
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motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?Thanks Mark. I have used a voltmeter on the DAC outputs to check that they are changing as they should be and there aren't any problems there. The problem only arises when the signals are input to the motor controller. I am using a screw-terminal device to interface to the DAQ card, a CB-68LP. Do you think I might have some sort of grounding issue to sort out?
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motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?That would have been my first guess, yes. First, I want to make sure that you have the correct pins, 54 and 55 are GND, and 22 is DAC 0 out, and 21 is DAC 1 out. Is it possible to monitor the output of the DACs when you connect your motor controller?

Mark
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motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?Good idea - with interesting results! When the DAC channel is connected to the motorcontroller input then the ouptut reads 12.8V irrespective of what the generated output should be. If I disconnect the controller input from the DAC, no voltage appears across the leads.
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motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?Well, I suppose two things could be happening. First, when there's no connection to the DAC, the motor controller input actually already HAS voltage on it, with sufficient current behind it that it actually is more powerful than the DAC, so the DAC can't lower it to the proper voltage. The reason your variable power supply would work is because it has a much lower impedance output than the DAC, allowing it to overdrive the motor controller input.

Either that, or there is a current coming from the motor controller input, and it is affecting the DAC because it's output impedance is not that low, and thus cannot "drive" the circuit hard enough, where your power supply can.

If you can find any information on your motor
controller, maybe you can see how much current it actually takes to drive it.

Lastly, I have had a similar situation before. Since you have a power supply that WILL work, can it accept a voltage input, and track it with its output? That's what I did. In essence, I just had a voltage "follower", and the power supply could output much more current, which was what I needed--it just gave me computer control of it.

Mark
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motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?Hello;

You should use the Continuous Analog Output Labview shipping examples instead. Those VIs execute a buffered Analog Output operation instead of the Software timed operation you are trying with your VI. You will need only to adapt the waveform to be output by the analog output channel to your needs.
Hope this helps.
Filipe
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motor controllers. However the controllers output full-scale as soon as they are connectted to to the DAC channels no matter what the channel output is. If I use a standard variable power supply I get a variable output from the controllers. What is wrong?With a bit of further investigation I discovered that I had a grounding problem between my motor controller and the DAC output. I have 12.8V appearing across the grounds of each. I'm hoping the problem can be solved by simply isolating the DAC output. I need to use the Write one update vi as the application is for real-time control.
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