Frequency measurement NI 9401

[Adryen]

Hello everyone, I´m sorry to create a new subject, i tried to find solution by myself everywhere, but with no success.

Iˇm trying to read a frequency with NI9401 and cRIO.

After i will set 800Hz on frequency generator (i did test it with oscilloscope, output is really 800) and i´ll connect it to 9401, I´m getting frequency which is jumping from +/- 793 to 823. (i connected CTR0 to pin 14 and ground to COM)
It does´t matter if i´ll set 50Hz, 500Hz or 5kHz, the "jumping" is still there. (Time on the loop is 200ms just to see the values, usually i leave it on 10but then, the values are jumping so fast it´s more like blurry number - illegibly).
Chassis is set on scan mode, i checked the electrical connection, cables etc, those things should be ok. I tried to put 9401 into DAQ and read freq. through NI max, and there, i´ll get 800Hz almost exactly. So i believe it is  cRIO and labview programming problem.
My question is, why is it acting like this ? Is possible to get "straight" frequency from 9401.. ? If yes, what should i change?

//..my amateur opinion, I have the feeling I´m getting "bottom and peek values of amplitude" from the graph (pic below), which is not what i want 🙂 .. but maybe you guys know how to get accurate freq from this or what else i did wrong. I´ll be grateful for any advice. Thank you. 🙂

I used example from here.

[vardanium]

It seems that you have sampling problem. What sample rate have you specified? The max. rate in scane mode is 1kHz, so you can't get very accurate measurements with that mode. So better to move to RT acquisition or, maybe, acquire signal with FPGA. For some details look here.