I'm using LM324 Q-op amp as a differential amplifier for measuring the voltages of 19-cell battery pack in series which happens to be 1.5 volt for each and the differential amplifier gain ratio is 1:1
Then all 19 op amps outputs are fed into 3 multiplexers 744051 with some sort of looping i got the measurements through STM32 3 ADC channels
The point is; amplifier output measurement has error of around 200mv So, how could i improve the accuracy?
Another point is; in my prototype i have an option to connect the battery ground to the op amp ground, when i connect it every thing is fine, and when disconnecting it, the lowest cells op amp measurements is too high around 5 volt which i couldn't understand why that happens
as far as i know differential amplifier doesn't need to be connected to the ground of the measured potential.
Note: I'm using a 20 volt single supply for the op amps
This is a simple illustration for the 19 cells schematic.
I'm using an ADC multiplexer, so I switch over each channel to get 8 cells measurement over a single ADC channel
When disconnecting batteries ground, my reference is op amp power supply reference as I measure a difference potential of the battery cell.