Re: How to Use an HP 400D R.M.S. VTVM?

joshhemming@xxxxxxxxxxx wrote:
I picked up an HP 400D R.M.S. VTVM at an estate sale. I’ve never used
one before, and I don’t have the manual for it.

The meter has a pair of jacks on the left front, with one labeled
INPUT and the one below it labeled G. There’s also a similar pair of
jacks on the right front, with the top one labeled OUTPUT and the
bottom one G again.

I’ve used multimeters and AC voltmeters many times before to measure
the voltage of my house wiring. I always stick the red lead in the
hot slot of a wall outlet and the black lead in the neutral slot to
get the reading. With this VTVM, however, if I stick the red INPUT
lead in the hot slot and the black G lead in the neutral slot, the
lead draws sparks from the outlet.

I figured there must be a short in the VTVM. But here’s the kicker:
If I stick just the red INPUT test lead in the hot slot of a wall
outlet, and leave the black lead disconnected, the meter reads 118
volts on the 300V scale. This appears to be a very accurate
reading.

So what’s the deal here with this meter? Is it designed to be
grounded with the G connector, and to use the INPUT to measure a
voltage by itself?

The meter may be faulty - download the manual (inc. circuit diagram) from here :

http://bama.edebris.com/manuals/hp/400d/

If you don't know how to check & repair the meter then find someone who can. If it was working properly, you'd be able to measure AC voltages from ..1 millivolts to 300 volts.


.

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