Analog input voltage fluctuation in myDAQ

-Hello !
I have a turbine blade rotation sensing and measuring device (i.e. picoturn) connected to AI4 pin of BNC 2110 I/O board. I am using a PXI-1033 chassis with PCI-6251 M series card in it. I have programmed an algorithm which acquires voltage from AI4 channel through DAQ Assistant and converts voltage into RPM.
Picoturn is connected to DC power supply (ranges 9 - 36V)
These are the following problems:
1. I will get error voltage readings if picoturn is connected to other channels except AI4 (i.e AI0,AI1,etc)
2. The reading of the voltage keeps on fluctuating between 0.49 and 0.51, in both the cases of when turbine is stationary and rotating.
3. If the power supply to picoturn is removed, even then I could see the fluctuations in the voltage reading from -0.0005 to 0.1 and above till I stopped running the program.
Could you please help me to solve these problems?
Attached is the VI of the program and manual of the instrument Picoturn.
Attachments:
Picoturn.pdf ‏515 KB
Analog_ RPM.vi ‏64 KB

Hello
What Error Voltages do you read when the picoturn is connected to other AI Inputs than AI4?
What are you using for the ground reference of your measurement?
Checkout this White-paper: http://www.ni.com/white-paper/3344/en/
Are you able to measure other analog input voltages from a different voltage source? e.g. a 1V DC signal from a power supply or a sinusoidal voltage from a frequency generator?
Regards
Corinne

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Attachments:
Subtract.PNG ‏1 KB

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Dear All,
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Attachments:
SV2.jpg ‏2305 KB
SV3.jpg ‏2305 KB

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=========================
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Attachments:
FinalCombined_2.vi ‏102 KB

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Attachments:
reflection coefficient and Vswr.vi ‏665 KB
front panel.PNG ‏66 KB
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gearing.jpg ‏162 KB

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Analog input voltage fluctuatio​n in myDAQ

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Analog input voltage fluctuation in myDAQ