Reading LEM current transducer

[gihlutax]

Hi, i'm having problems measering current using labview FPGA.

I have a LEM CKSR 25-NP current transducer. I supplied a 5V supply voltage to the LEM current transducer, and the reference voltage of 2,688V
So when Ip = 0A, Vout=Vref+2,688V the sensitivity is 0,025v/A so when I have 1A the Vout will be 2,688 + 0,025 = 2,713V.

I have a CRIO with an analog input module NI9223, where I have the reference voltage and the Vout to measure the current.

When I measure the input voltage ( I created an indicator from the FPGA input node), the input voltage is varying.

when the current is 0A the value indicated is 2,6XXX, the X are varying. Though when I measure with simple voltage meter I measure 2,688V.

I hope I was clear enough and someone can help me further.

Thanks.

[AJost]

The 9233 is made for IEPE sensors, which means that the module will output a 2mA exitation current on the BNC connector, which you can't switch off on the 9233.

Please refer to the manual for more information

http://www.ni.com/pdf/manuals/373784f.pdf

I imagine, that this will cause serious issues with your measurement set-up and it can easily explain the large amount of noise you see on your device. And I fear there is no way around with this module.

Andreas Jost

Applications Engineer

National Instruments