Problem in getting accurate measurement using NI 9227

[Deepa_Krishnamurthy]

Grounded the shield of all four Lapp cables to one of the sensor's ground.

[CFER_STS]

Grounding a cable shield will reduce externally induced noise, but that is not the same as a ground-referenced signal, in which the current signal analog input negative / common end is tied down.  Refer to the wiring diagram in the Operating Instructions and Specifications manual for the NI 9227.  It is possible that your problem is the result of common mode voltage differences between channels.

[Deepa_Krishnamurthy]

Thanks for your input.

I will try grounding Al- of all four ports.

[Deepa_Krishnamurthy]

I could not solve it yet.

I even tried grounding all the four AI- to ground of one sensor, but the output is still the same. Sometimes I get correct values from 3channels and sometimes I am not getting it whether I ground them or not. One of the channel always is providing 0.15mA difference. Even other channels provide 0.1mA difference.

I couldn't figure out what is the mistake I am doing.

[Henrik_Volkers]

Please provide a schematic of all your cable connections...

[Deepa_Krishnamurthy]

Please find the attached schematic below

[Henrik_Volkers]

Powersupply?

[Deepa_Krishnamurthy]

Power for the CDAQ chasis and the devices which produces (D1-D4)4mA-20mA is provided(230V 50Hz). I forgot to mention them. Sorry.

[Henrik_Volkers]

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@Deepa_Krishnamurthy wrote:

Power for the CDAQ chasis and the devices which produces (D1-D4)4mA-20mA is provided(230V 50Hz). I forgot to mention them. Sorry.

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No problem just include them in the schematic as found (and not as remembered 😉 :D)

[CFER_STS]

Have you tried using the shipping example to see if the readings are consistent?

Example Finder / Hardware Input and Output / DAQmx / Analog Input / Current - Continuous Input.vi