Max current allowed when reading an analog voltage

3 posts / 0 new

Fri, 04/06/2018 - 14:47

florian_BCD

Hi all,

I am a bit confused and would appreciate a clarification on the matter:

Is there (and if there is, what is it?) a maximum current allowed when reading a voltage value; on both AIN pins and FIO ones?

I know there is obviously a maximum voltage that can be read (-10 to 20V special range for AIN pins; and 0 to 3.6V special range for FIO pins); but I was wondering if that comes with a current limitation?

Thanks,

Fri, 04/06/2018 - 16:20

LabJack Support

The currents that flow in/out

The currents that flow in/out of an analog input are called bias currents. Small currents must flow in to or out of the analog input so the connected signal can move the charge of input to the correct voltage. The bias current is dictated by the analog input. That is, the analog input will dictate how much current flows in/out of the analog input. On the U3, the analog input bias currents are on the order of 10 uA on the high-voltage inputs and much less on the low-voltage inputs.

For example, look at this diagram. You might have 1 amp flowing through the circuit and the measurement shunt, but only 1 uA is flowing into the DMM:

http://3.bp.blogspot.com/_06weV6RUhf0/TGOzirv_DmI/AAAAAAAAAHk/OVVIZ9acPQ...

Fri, 04/06/2018 - 16:32

florian_BCD

Hi,

That makes sense. Thanks for your help!