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Analog Input Signal Issue

Hi Everyone,

I am having a small problem that has troubled me for awhile now.

I use LabVIEW 2016 and 7853r FPGA card. I have 4 stable signals from 4 different femto preamplifiers hooked up to a quadrant photodiode. I feed the signal to labVIEW through SCB-68 connector. I use SHC68-68 RMIO cable to connect the SCB-68 to the Chassis (NI PXIe-1062Q).

My problem is, when I check the signals via a multimeter or oscilloscope, I get a stable signal, but when I check the signal in LabVIEW FPGA using the code attached the signals fluctuates a lot, sometimes giving negative values. What could be the problem?

Any hint or ideas will be highly appreciated.  Thank you.

 

Opuk

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Could you provide some examples how the measurement looks like and how it should look like (as seen with the oscilloscope)?

 

The issue might be with the termination (RSE/NRSE) of the input for example.

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I am also seeing you are not applying a scale to the reading.  You are just seeing the actual ADC bits.  Any little noise will cause those bits to toggle.  If you applied a proper scaling, that toggling might not look so bad.

V = Count*10/32767


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Helo Nikodem,

Thank you for your response to my question. Attached please find the sampled measurements for my data. I expect the data to be a constant but the fluctuation is just crazy.

 

Kind Regards,

Opuk

 

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Hi Crossrulz,

Thank you for finding time to respond to my question. I have tried applying a scaling as suggested but in vain.

Thank you.

 

Kind Regards,

Opuk

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