Multimeters, What a concept!
Proper selection, use, and care of electrical testers is important
By Jim Sparks
Like most involved in the aircraft maintenance field, I started out as an inquisitive little tyke with a fond habit of taking things apart. One day, after spending a significant amount of time trying to get a friend's transistor radio to operate, I climbed on my bicycle and pedaled up the road to the local electronics retailer. It was my suspicion that the battery was dead but with the price of a nine-volt battery being about half of my friend's weekly allowance, I did not want to take any unnecessary chances. The sales clerk, after hearing my dilemma, reached into the showcase and withdrew a fantastic gizmo. It had neatly folded test leads and a display that had lots of numbers and a mirrored background and even a selector knob that had about a million different positions. The man behind the counter had removed the suspect battery from the radio and connected and adjusted the mirrored gadget, then told me that the battery was indeed depleted and would need to be replaced. I, on the other hand, was no longer concerned with a mere battery. I wanted a closer look at the mirrored marvel. He
called it a V.O.M. and said that complete with test leads and battery it could be mine for $5.65. My birthday had already passed and Christmas was a ways off. Fortunately, I had a father who also liked to tinker and was equally enthused about the fantastic little gadget. Under the premise that the directions would be read carefully and the device only used under supervised conditions, my father bought me my first V.O.M.
It was only after reading the directions that I learned V.O.M. actually had a meaning, Volt, Ohm, Meter and was also known as a Multimeter. It could be used to test things called voltage, amperage and something called Ohms. I observed that anytime I selected the scale that had to do with Ohms, I could touch the two test leads together and make the pointer deflect all the way to zero on the mirrored scale. About a year later, a friend of mine who was old enough to drive purchased an old, used car. Unfortunately, the headlights would not come on when the switch was activated. I selected the scale labeled as Ohms and connected the test leads to each headlamp and observed meter movement. That told me the lamps were okay. The next step was to connect my V.O.M. to the light switch. Unfortunately, I connected the Red test lead to the light switch while the Black lead was resting on the uncarpeted floor. When I did install the black wire, there was no meter movement. I then removed both leads and touched them together as I had done many times in the past. Again there was no movement. I went
back to the store where I purchased my meter and then ask the guru behind the counter why my V.O.M. no longer worked. This time he pulled out a Phillips screwdriver and removed the one screw that held the back on. After careful scrutiny, he informed me that I had blown a fuse. He then asked if I had used the meter as illustrated by the directions. I informed him what I was doing and was promptly reprimanded for having the familiar Ohms scale selected while connecting the meter to a circuit that had power applied. It was then made clear to me that anytime I connect a meter, it is always best to select the highest range of the voltage scale to see if any potential is available. If it is confirmed that the circuit is dead, then go to the Ohm scale. The cost of this lesson involved spending 59 cents to replace my blown fuse, plus have one as a spare, and listening to a 10-minute dissertation on how to properly use my meter.
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