Can I control the voltage being output by the PCI-4451? If I can control the voltage are there any sample apps that illustrate how? What is 'update rate' in the Measurement and Automation explorer and why does the output voltage fluctuate based on it? I have a PCI-4451 connected to a BNC-2140 and have been unable to control the output voltage. I have the output from the BNC-2140 going into an osciliscope to verify my waveform's amplitude and frequency. Using the Test Panel in Measurement and Automation explorer I have been able to generate a sine wave that went from about -9 to +9 volts at an 'update rate' of 15 kHz - I had requested voltage from -10 to +10. When I reduced the 'update rate' the voltage dropped to a measured range of -1 to +1.
When I tried controlling the voltage in software using the ActiveX controls I was not able to impact the voltage at all.
The "update rate" parameter in Measurement and Automation Explorer determines how often the 4451 board updates the voltage on its analog output line. This value is not equal to the physical frequency of the analog sine output, but it is directly proportional to it.
I tried a wide range of update rates using the 4451 attached to an analog oscilloscope and I did not see any change in amplitude at lower update rates. It sounds like very low-frequency signals may be experiencing some filtering in your circuit. You can expect this if you are feeding into an oscilloscope set for AC coupling.
There are several examples available in LabVIEW, ComponentWorks, and LabWINDOW/CVI for programminmg analog output. In LabVIEW and ComponentWorks, you can use most hardwar e-timed analog output examples for your DSA board. If you are programming in CVI, I would suggest taking a look at our example program available in the Developer Zone (search under "DSA" and "output").
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