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DC offset on input of 5782 module

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Hello All,

 

I'm using a flex rio system with a 5782 module ( the DC coupled version)

We have some trouble with the analog inputs AI0 and AI1, we measure a DC voltage of 250 mV on both inputs.

The module has been returned for repair but no problems were found.

I wander if other modules have the same "problem" so is there anyone out there that can do this simple test:

Disconnect your cable from AI0 or AI1 and measure the voltage on the bare input terminal with a simple multimeter.

If other modules also have this Dc offset then it's probably the "nature of the beast"

 

Thanks in advance for any reply's.

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Solution
Accepted by topic author Flow_Cat

I measured +250 mV DC offset on the AI0 and AI1 inputs of my DC-coupled NI 5782 also. NI should have included that in their spec sheet.

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Thanks dr_b,

This indeed confirms that all DC coupled NI5782 modules have got this DC offset.

This was also the conclusion of the NI service engineers that helped me, and I must admit that I forgot to post this conclusion.

Meanwhile we changed our hardware connected to the inputs and created a work around for the offset.

So my problem is "solved" but I agree that NI should have mentionned this in the specs.

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Hello, i have been going through same issue and i finally stumbled upon this. I thought there was a problem with the impedance mismatch, but it seems it starts to make sense if there is a DC offset internally in the input.  See attached picture, when i plug in the AI of the 5782, there is a shift on the original sine wave input.

 

ImpedanceIssue_w_5782_connector.png

 

 

My second question is what did you do for the workaround?

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I had to add an analog level shifter circuit.

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