Unable to acquire constant values on FPGA on the CompactRIO.

[TridentHappy]

Created a VI to acquire data from the NI 9201 Analog Input module on the  FPGA target using CompactRIO 9004 and Chassis 9014. We used DMA FIFO to transfer data from the FPGA Target to the RT. In RT, we read this FIFO and then passed this data to the binary to nominal vi. A possible problem might be that the binary to nominal vi is acvquiring data in fixed point form directly from the FIFO read and hence calculating wrongly. So we put indicators after reading the FIFO to check the fixed point values. A 5v constant input was being read as 4-5. But there is a lot of unreasonable variation. Is there any extra step i need to take to convert this fixed point to binary? Is there anything wrong with the DMA FIFO timeouts? I am attaching all the relevant VI's.

[TridentHappy]

I've been trying again and I've got the issue with the DMA timeouts sorted out. Now I atleast get the same value that I get on FPGA on the RT host vi. However this value is always changing even though I've wired a constant 5V supply.

I don't know whether I should attach something else and if I've given all the relevant information and I suspect it's a very very simple error on my part but I've spent two days and can't figure it out yet.

[Shreyas · Accepted solution]

Hi,

    What is the range in which the values are varying? Also putting a low pass filter would help you reduce the noise if you want to measure DC voltages only.

[TridentHappy]

I tried with a different voltage source and a low pass filter and it's working now. Thanks.