Testing trigger voltage

In article , (Floyd L.
Davidson) wrote:

Specifying impedance that way is nearly useless if the number changes
for every range.

No it is not. It is just more wordy. It says *exactly* the same
thing.

Floyd-

You are *exactly* right! However, knowing the Ohms-per-Volt is only
important when using a meter where that value is constant.

When using a meter with a constant input resistance, you are wasting your
time doing the conversion (unless you just want the practice). Input
resistance is the value you need to know.

Fred

Kennedy McEwen writes:

You probably know them better as "Megger", which is even what most of
the younger electricians over here refer to them as, these days:
http://www.megger.com/us/about/index.php

I've seen a hand-cranked Megger insulation tester, and I think those are
well known here. The "about" page says that was the company's first
product.

their digital AVO range has slightly
lower in input impedance at 7.8MOhms than most DVMs, such as those by
Fluke and others.

What an odd value! The 11 M input DVMs get that by using standard 10 M,
1 M, 100 K, ... precision resistors in their divider, for a total that's
actually 11.11111... Mohm. The 10 M input DVMs provide a slightly
easier number to work with in loading calculations, and in theory it's
exactly 10 M, but the divider chain is built using 9M, 900 K, 90 K, ...
To get 7.8 Mohm total, while still giving 10:1 steps, the divider would
have to be 7M, 700K, ...

Dave

Awww, you guys.

You've done it to me. All this talk of analog vs. digital voltmeters
reminded me of my years joyfully using analog instruments. You know,
the ones with real, live, honest needles.

I'm an electronic hobbyist. I own a high-end DVM - a Fluke 187. Love
it. It has a bargraph display that simulates an analog meter, but
when I'm "adjusticating" something, the feel just isn't the same as it
was when I used to watch a needle move up and down. Reading this
thread made me realize that I miss that feeling. So I just orderered
an analog VOM!

My justification is that I can stick it in the glove compartment to
have in the car if it breaks down. But with the plumbing and computer
hiding under the hood, I wouldn't know where to start troubleshooting
a dead engine. (Years ago, I could repair just about anything that
broke on my car. These days, my automotive troubleshooting checklist
is to look at the gas gauge. Gas in the tank? Air in the tires? If
yes, get out the cellphone. Fortunately, with modern automobile
technology, the term "troubleshooting" has become an abstract
concept.) But it's at least a tangible reason to add another test
instrument to my collection.

Mostly, though, I want to watch that needle move up and down.

Gotta run. I need to build something that needs adjusticating before
the VOM arrives.

Tom