Voltage measuement advice (USB6216)

[lvrichard]

Hi All,

Please advise,

I am having some difficulty measuring a votlage using a USB 6216 (A task which i usually do not have an issue with). Please see attached pic.

The device under test is a 12 volt power supply with the secondary side optically isolated from the mains votlage side. I am placing a votlage divider at the O/P (220k/100K) and measuring the voltage over the 100K resistor, differentailly using AI1+ and AI1- as shown. I have have connected the AI reference to ground (also shown).

Can someone please advse me if this is good/ correct practice or not ? My measurments are not as stable as i would like...

thanks in advance.

[crossrulz]

You will have issues with ghosting and other noise due to the divider making a high impedence source.  I would add an op-amp in a voltage follower configuration to create a single ended signal that will also have a low source impedence.