# A question about differential ended settings for single ended inputs

Reading this documentation, what could be the reason to use 10k if one uses differential ended input settings for signal sources?:

I dont know why they recommend 10k but I had 6 channels going to this board from single ended 6-axis force transducer system and the signals measured were very clean. But when I added some other transducers to rest of the channels such as temperature, humidity ect. transducers, I started to have more noise and 50Hz noise. All inputs to the daq are single ended( the transducers' grounds are not earthed so no ground loops expected) and BNC coax cables used.

In my case I had shorted all channels' CHLow to LLGND but they recommend 10k resistor, could that be the reason? What could be the 10k resistor's function?

edit:

I tried to make a simulation regarding Spehro Pefhany's answer:

(left click to enlarge)

I couple EMF to both lines, and Rx is the recommended 10k.

If I dont use 10k and short CHLow to LLGND I obtain noisy output(red plot):

If I use 10k the 10k develops a common-mode and the output(red plot) doesn't have the noise:

I haven't tried this 10k in practice yet though.

• You MUST provide some current into the two input pins of the amplifier. Perhaps only picoamps if the amplifier is FET-input, tho at 125 degree Cent that input current will increase 1,000X if not 1,000,000X. – analogsystemsrf Dec 21 '17 at 2:29

The value of 10K is not magic. Values as low as 50$\Omega$ are used sometimes- just enough to prevent serious ground loops in the case where the grounds are not isolated from each other. That's called a pseudo-differential input.