On Wed, 22 Dec 2004 04:47:04 +0000 (UTC) Damian Menscher
wrote:

Jim Adney wrote:

How about 547? Does that sound any more familiar? ;-)

No, it's definitely a 647. Got it right here in front of me. Looks
to be one of the earlier ones, judging by the serial number.

It has a strange malfunction which I've been trying (unsuccessfully)
to correct for the past 10 years or so. I'll start a new thread about
that, though, since it has little to do with this thread.

Is this a solid state scope?

You'll have to explain to me how to use the meter as part of the
chain... that doesn't really make sense to me. Also, doesn't that
impact the safety of the measurement?

Think of ten 10 MOhm resistors in series. Each one sees 1/10th of the
total voltage. Now replace the bottom resistor with your meter, which
just looks like a 10 MOhm resistor when you put it in a circuit.

Now your meter reads out the voltage it sees across itself, which is
1/10th of the total. So the total voltage is 10 times the meter
reading.

As long as you keep your fingers away from the upper resistors, I
don't think you're in any real danger at the voltage levels you're
talking about here. Of course you need to make sure that the low side
test lead of your meter is securely grounded before you start this.
Otherwise, the meter itself will float up to the full voltage.

A better probe for high voltages would actually have a 990 MOhm
resistor. Then you get to multiply by 100, and there is even less
loading of the test point. But resistors for this will be much harder
to find. A probe made to work to 40 kV would be made like this.

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Jim Adney
Madison, WI 53711 USA
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