NI FGEN Off-Set Range

Updated Sep 20, 2018

Reported In

Driver

  • NI-FGEN

Issue Details

I have a PXIe 5413 and according to the spec sheet, the offset range is +/- 50% amplitude range, and the range is 0.0155V to 24V for an open load. However, if I set the input to amplitude=18mV and DC offset to 2.7V I get an error saying the offset is out of range. It is saying that the valid range is half of my amplitude, +/- 9mV in this case, which is not half of Amplitude Range as stated in the specs.

It seems that the calculation of valid DC offset in the driver is wrong. It calculates a valid DC offset as 50% of selected amplitude rather than 50% of full range.

Solution

In order to get an 18mV amplitude sine wave with 2.7V offset,you would have to generate it through a custom waveform, where you can set the range yourself. You can do this by using the NI-FGEN in Arbitrary Waveform mode, however, the resolution of the signal will be compromised if you decide use a rang that will allow for a 2.7V offset for an 18mV signal. 

For more information, a discussion forum on this issue can be found here.

 

Additional Information

When you create a waveform with a standard waveform generation, the FGEN driver automatically uses the best possible range it can to represent the signal. If you have an 18mV signal, then it will set the range such that it provides the best resolution for your wave, ie the range will be quit small, which is why it is telling you it is not possible to use 2.7V as an offset as it is out of range for the range FGEN has chosen for you. 

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