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| Multimeters: Part-Deuce |
| Written by David Jackson | ||||
| Tuesday, 23 October 2007 | ||||
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Watt matters the most?
Multi-meters: what are they? Multi-meter is a generic term for the hundreds of models of electronic measuring devices used to study electricity. Each year these instruments become more complex and feature-laden, while mass production lowers the cost. Even the humble modder can have at least one in his or her toolbox. So, what kind of meter should I buy? The answer to that is… it depends. It depends on the measurements you plan to take, what you can afford and how or where you are going to use it. You wouldn’t want to buy a $3000 bench-top meter with an oscilloscope, and then try to use it to install a car stereo. Nor would you use a $15 cheapo from that um.. Shack place to troubleshoot a logic board problem. Features Now this is strictly my opinion, but I would say the two most important features to have in any meter are voltage (both AC and DC) and resistance. This is based on my experience as the settings I use the most in my hobbies and my profession. Next would be amps, followed by millivolts. Let’s kick some tires OK, there aren’t any tires to kick, but let’s take a look at some models I am familiar with.  Hardly a multi-meter, but still at the top of my toolbox, this little tester detects the electromagnetic fields around wires when they are charged. It is great for those “ is it hot” situations. Just hold the end near a wire that has current flowing through it, and it lights up and “beeps”. No current = no beep.  Clamp on amp probe, reads amps voltage and continuity (more on continuity later)  This is a true multi-meter; reads voltage, resistance, amps and milliamps, and has an rs232 port for data logging.  Very simple auto ranging meter, reads volts and ohms. Next is the latest in my personal collection a very nice clamp on amp-volt-ohm meter:  Although it looks simple, it is quite versatile and covers all the primary functions I require in my meters. It has a data hold button that is very useful for taking readings with the clamp inside a panel where you cant see the display. Simply clamp it on the wire to be read, and push the hold button. Un-clamp it and read the frozen display. Push the button again to un-freeze the display.  Now this old guy here is from the ‘70s and has been in my toolbox since I was a teenager. I got this as a gift around my 13th or 14th birthday. It still works great. Oh and that great big thing with the needle in it? That’s an analog display. This meter reads volts, AC and DC, ohms and milliamps. And it has a battery test function. There are a great many more types of meters and testers out there beyond the few I have shown here, from mega ohm meters used to test among other things, the windings on motors, to sign wave current analyzers running on the thousands of dollars. Safety Before taking any measurements or readings, a few words about safety. Always set the meter to a higher range than the expected voltage, then turn it down after confirming the actual voltage. If you have an “Auto ranging” meter, this is not necessary. When reading high voltages, set the meter down, or hang it where you can read it. Why? I have seen faulty meters burn up and nearly explode when reading voltages above 440 volts AC. Obviously, be very observant of the area around yourself, and eliminate any distractions. You don’t want to be startled and touch the wrong thing. It only takes milivolts of current to stop your heart. There is plenty of current in a Mac power supply to ruin your day. Basically, be careful and know what you are doing. Take a basic electric course if you have a real interest; the hands-on training you will get is far better than anything we can cover in this column. This week we looked at some of the different types of meters available and briefly touched on safety. Next time we will grab some schematics, turn on our meters and see what’s up in that sub atomic world of flowing electrons called electricity. ‘till then, Keep moddin’!
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