AnsweredAssumed Answered

measuring small voltages

Question asked by davebrobst on Jan 25, 2009
Latest reply on Feb 20, 2009 by Frank_BR
In browsing the forum, I think I have found the answer to my question, but would like verification.  The question boils down to:  When measuring a small AC voltage riding on top of a large DC bias, cranking the scope's volts/divsion down and the DC offset up for the channel up to see the AC voltage full screen, an unavoidable non-linear error is introduced into the signal, correct?

If the above is correct, the only way to get around the problem is with a differential probe, correct?

As an application background, I am trying to measure the current in a battery-powered system.  I am measuring the voltage across a 10 ohm resistor on the high-side of the system.  The current is on the order of 100uA, but has higher power surges of about 3mA.  The battery voltage is 3.6V.  In looking at the signal on the scope, if I try to do a (channel 1  - channel 2) operation, when I am zoomed into the signal, I get vastly overstated readings (compared to multimeter readings and calculations).  Is the only way to measure this particular setup with a differential probe?

If the differential probe is the only way to measure this setup, can I get away with an N2772A probe, or do I need one of the higher end differential probes?


Dave Brobst