Hello all, this is my first post here and I swear that I used a search button and read a whole bunch of articles regarding grounding issues.
Background:
I'm trying to measure an analog signal between 20 and 30 kHz into a PC via Digital Acquisition(DAQ) Board. Before A/D conversion signal is filtered and amplified through my home-built filter/amplifier board. This filter/amplifier board is largely based on 741 OpAmps and requires +12 and -12 voltages to operate.
Problem description:
Once the filter/amp board is connected to laboratory (earth grounded) power supply - everything works fine. However, it is supposed to be powered by two 12Volt batteries and be a mobile system, then when it is connected to two 12V batteries filter board's output becomes noisy and drops down significantly. What happens next is very puzzling for me: When I connect "Common ground" between batteries to "Earth ground" from 110VAC wall plug, everything becomes normal.
Can I somehow improve my filter output without connecting it to wall earth ground??? It has to be a mobile solution.
Here's AC-ground output:
Here's "wrong" battery-ground output:
Here's the setup:
Background:
I'm trying to measure an analog signal between 20 and 30 kHz into a PC via Digital Acquisition(DAQ) Board. Before A/D conversion signal is filtered and amplified through my home-built filter/amplifier board. This filter/amplifier board is largely based on 741 OpAmps and requires +12 and -12 voltages to operate.
Problem description:
Once the filter/amp board is connected to laboratory (earth grounded) power supply - everything works fine. However, it is supposed to be powered by two 12Volt batteries and be a mobile system, then when it is connected to two 12V batteries filter board's output becomes noisy and drops down significantly. What happens next is very puzzling for me: When I connect "Common ground" between batteries to "Earth ground" from 110VAC wall plug, everything becomes normal.
Can I somehow improve my filter output without connecting it to wall earth ground??? It has to be a mobile solution.
Here's AC-ground output:
Here's "wrong" battery-ground output:
Here's the setup: