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Building safe meters

By Chuck Newcombe

It has always bothered me a little to be referred to as an expert.

Besides the obvious old tired definition of the term ("x" is an unknown quantity, and spurt is a drip under pressure), I have the feeling that I'm misrepresenting the truth of the matter. What I know, or seem to know, is the direct result of my powers of observation, a latent curiosity, and, so far, a reasonably good memory. I think it may also be referred to as experience. (Ok, maybe that's what an expert really represents.) I'd like to give some examples of how expertise may be gained.

I regard each of my readers to be a potential contributor to my own continuing education. By that I mean you each have insights and experience in areas that I know nothing about. And that's what I'd like to talk about for the remainder of this column.

Knowledge often comes from mistakes.

The first mistake relating to electricity that I can remember from my youth was the time as a five year old when I unscrewed a light bulb and stuck my finger in the socket. I liked the funny feeling I experienced in my finger. I learned that was a mistake when my parents punished me, but I didn't understand until years later how dangerous my experiment had been.

The next mistake was the day when I was about 10 that I attempted to make a light bulb. I had just heard the story of Thomas Edison and his quest to do the same in 1879.
I knew the basics - a filament enclosed in a vacuum so oxygen wasn't present to burn it up. What I didn't know was Ohm's Law.

It was an elaborate experiment - a candle in a pie tin partially filled with water. The end of an old extension cord was routed under the lip of an upside down Mason jar immersed in the water, rising out of the water inside the jar with a sewing needle (filament) connected between the stripped ends of the wires.

The experiment went something like this:

  1. Light the candle and quickly place the jar over the assembly until the mouth was closed by the water.
  2. Watch the candle burn (and the water rise in the jar) until it extinguished for lack of oxygen.
  3. Plug in the extension cord to light my bulb.

Well, you know what happened. There was a bright flash as the jar jumped in the pan - vaporizing the needle and spraying water all over me and the kitchen counter where I was working. Then, of course, the kitchen went dark because the fuse in the fuse box blew.

My dad didn't actually punish me so much as he carefully explained Ohm's Law until he was sure I understood.

I hope you're getting the idea by now. Much of what I know resulted because of mistakes made by me and others over the years. Unfortunately, there have been injuries and damage as the result of some of those mistakes; mistakes that happen because of a lack of knowledge or impatience.

Consider the case of the blown fuse in your multimeter. It's certainly an inconvenience when you discover that you can't complete a current measurement because the fuse is blown in your meter. All too often, the temporary fix is to wrap the foil from a stick of chewing gum around the fuse and continue with the measurement. That can be a disastrous mistake, particularly when combined with another mistake, that of attempting to measure the voltage on a 480 volt panel while the test leads are in the wrong jacks on the meter. The arc flash that may result can be deadly or at the very least painful, if you're extremely lucky, as I was with my thrill seeking exploration of the light socket, or my crude light bulb experiment.

Each of the safety features you find in your Fluke DMM and its test leads resulted because we learned from the experiences of others in the electrical industry. Sometimes those experiences were because of mistakes, but often it was simply a lack of complete understanding about the physics of the situation, as it was in my childhood experiences.

You folks are lucky. With such information sharing tools such as Fluke Plus available, you can gain insights into the mysteries you encounter on a daily basis. I'm learning much from the "Tips from Fluke Users" threads, and the several case studies that appear there and in other Fluke publications these days. If I were still defining new meters for Fluke, I'd be all over this resource on a regular basis.

I guess the latent curiosity I spoke of at the beginning of this piece is still alive and well within me. I find myself wanting to experiment with some of what I read in Fluke Plus, in order to gain first-hand experience that I might then remember.

I hope you're finding it useful as well.

Chuck's Favorite Articles

A million and one uses for voltage detectors »
This simple tool can save lives - check out the innovative uses that Fluke customers have submitted.

Floored: Insulation Resistance Meter tests for electrostatic discharge »
A creative use of an insulation resistance meter that also details the before and after testing process (verification) that should be followed with any major installation.

Choosing the correct fuse for your tester »
Foil around a fuse is dangerous, but so is substitution of a cheaper fuse.

Temperature tools give engineering firm the competitive edge »
Besides safety, relatively inexpensive Fluke tools can help make your business more competitive