ECN Forum Forums General Topics of the Trade General Discussion Area Multimeter

Paul,
I have an old meter here, that was one of the first to use Field-Effect-Transistors (FET's).
It gives a centre zero option, although I've never used it before, it also has a polarity switch on it too.
It says on the scale that it will measure up to 3000VAC, personally I would never use it to that level of voltage.
However,
One thing my younger brother learned in a hurry when I first started my time as an Electrician, don't plug your older brother's meter into the 230V socket and expect to measure how fast the amps are coming out of the socket on the resistance range.
There was a shower of sparks and a blown fuse at the switchboard and a useless meter.

Most VTVMs or FET equivalents allow that. The polarity reversal is needed so that you can measure voltages positive or negative with respect to the chassis with the shield of the cable/probe on the latter (e.g. negative A.G.C. or grid bias voltages, or most voltages on those older transistor units based around PNP transistors). There's normally enough range provided on the zero adjustment (the electrical one, not the mechanical one) to bring the meter up to center zero (with suitable scale provided).

I still have an old Leader VTVM (mid 1960s) which I use for radio work.

And of course, when making that chassis connection you need to make sure it isn't a live chassis, odervize ist spitz und sparken mit poppenfusen!