Here is a differential multimeter from fluke. I have tried to cover most of the repair circus in the video below.
However, this blog is to track any bugs/details I may have missed in the video.
I tested this (without calibrating) against my Agilent 34401A and the voltage and current readings were very close. Resistance needs calibration.
Few simple explanations here. What is a differential meter ? Lets compare it with weighting scale.
This is a direct weighing scale or direct measurement multimeter
And here is the differential multimeter of weighing machines
The idea is to measure the unknown using a known precision measurement or weight. Which we call as the standard weight.
In a differential instrument, this is implemented using a reference voltage source – equivalent to the standard weight. Then a precision divider, so that you can create sub weights of the main weight (aka 1kg, 100g, 10g, 1g). In electrical sense this is accomplished using a precision divider.
The third piece is the balance arm, which is the null detector in the multimeter.
So here is the block diagram
The left side is the input, which is the “unknown” weight connected to the “arm” aka null detector. The right side is the reference source + precision divider aka standard weights.
The difference between them is displayed on the meter, and you adjust the precision divider to match both sides to “null” or balance the meter, and count the standard weights you have used to figure out the unknown input.
Lazy Electrons 