I have this DVOM:
http://www.rpelectronics.com/Default...s/PM-1029A.asp


DVOM uses 9V for power display and electronics

A 24v battery and a linear voltage regulator (set at 9V) feeds the circuitry of DVOM. I can measure any DC voltage within its preset range (0 to 200V) as long as that is part of separate circuit, say a battery, another power supply etc.

but when I try to measure the voltage on same battery pack that feeds the voltage regulator the DVOM digits disappear and only couple of segments are displayed in first digit.
removing the ground DVOM probe from the circuit restores the digits to "0000".


apparently negative/ground for 9V DVOM and negative/ground probe do not play well.


so, how do i isolate those two negatives from each other so that I can measure the power from same battery pack that feeds the DVOM via voltage regulator?

Buy a dPm that includes the isolated power supply. Or build a switcher with an isolated winding on the inductor