how to measure millivolt with Labjack (U3-HV)

3 posts / 0 new

Fri, 09/14/2018 - 01:36

MinC

Hi all, I'm coming here for advice. I connected the positive to AIN1 and negative to GND in order to measure a very small Voltage signal, in the LJLogUD interface (in Ch1) I'm getting two different values that shift constantly from one to the other and are in no way representative of what I'm measuring. I went through the 'Ranges' dropdown menu but that doesn't seem to help. I imagine this has to do with the fact that the resolution of LJ is not enough to register the range I need (0.0001 mV to 10mV).

May this amplifier help (link below)? And if so, could you confirm that I can connect two sensors with each amplifier?

https://labjack.com/accessories/ljtick-inamp

Or are there any other possible solutions?

I'd appreciate your help, thank you

Min

Fri, 09/14/2018 - 10:48

LabJack Support

I believe you are correct

I believe you are correct that the U3 is unable to resolve the signal that you are looking for. An inAmp would make a big improvement. You are also correct that the InAmp has two channels.

Mon, 09/17/2018 - 09:57

LabJack Support

Assuming you are talking

Assuming you are talking about AIN1 on a U3-HV, that has a normal range of +/-10 volts, which is a span of 20 volts. Taking 20 volts divided by 12-bit resolution (4096 steps) you get a resolution of about 5 mV, so not very good for a signal that is only 10 mV max.

You could do a little better on a low voltage channel, say FIO4, but still not good enough. You would have to do a differential since you are so close to 0 volts:

https://labjack.com/support/datasheets/u3/hardware-description/ain/analo...

... and thus your resolution will be about 1.2 mV:

https://labjack.com/support/datasheets/u3/appendix-a