[Craig Sawyers]

Here you go. Ignore the blue lettering - I was using this for a different application.

Anyway R1 is what the tester originally wants to see (in my case 1k).

Anyway, the way it works is that the voltage across R2 has to be the same as that across R1. R2 sets the current through the meter.

In my case the donor meter was ten times less sensitive than the (open circuit) original. So the voltage that the original saw was 0.1v. So 0.1V across 100 ohms is 1mA - the current sensitivity of the donor meter.

RV1 sets the zero, R3 is a current limiter to prevent the donor meter burning out if there is something wrong somewhere - it limits the maximum current to 2mA - so a x2 maximum overload. The rest is just power supply stuff.

Craig