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Digital Multimeters


A Digital Multimeter is the best weapon you have in fighting those electrical and electronic gremlins that sneak into your vehicle.
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» Part 1: DMMs
» Part 2: Using a DMM
» Part 3: Volts & Ohms
» Part 4: Wire Checking
 

This week I'd like to talk about using a Digital Multimeter (DMM). With engine management systems being electronic it is one of the most powerful and versatile tools at your command. With a good wiring diagram and a good multimeter, you can find the cause of almost any problem be it electrical or electronic.

There are two basic types of multimeters, digital and analog. Analog multimeters have a needle and the digital has an LCD or a LED display. With today's vehicles it makes more sense to have a DMM but an analog multimeter still has its uses.

In the old days a meter was used mostly to check batteries and dwell angles. A mechanic might have gone days without taking his multimeter out. Today that has changed. Today a good multimeter is an essential part of a mechanics toolbox. Today there's hardly a day goes by where I don't use my meter at least once.

A DMM will have many functions built into it, and since there are many brands and types of DMMs on the market, I will only go into the basics that they all have in common. As with any tool or piece of equipment make sure you read and follow the instructions and cautions that come with it. This will protect you and your equipment.

All DMMs will test for voltage, current and resistance. These are the three functions you will use most when trying to diagnose a problem. When you purchase a DMM, one of the most important things to look at is the meter's impedance, which is the meter's operating resistance. Most DMMs have very high impedance. Since the meter is part of the circuit being tested, its resistance will affect the current flow through that circuit.

If a DMM has a very high impedance or resistance it will cause a slight increase in the circuit's current. This becomes a concern when you test electronic systems because the increased current draw can damage the components being tested or, at the very least, alter the readings or change a sensor signal. You want to get a meter that has an impedance of at least 10 megaohms. That is to say their current draw is so low it becomes invisible.

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Part 1       » Part 2       » Part 3       » Part 4
Additional Information provided courtesy of
ALLDATAdiy.com and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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