DMM Help

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DMM Help

Post by Lego4kid » Tue Nov 05, 2002 5:42 pm

I'm planning on purchasing a new DMM, and want to get an idea on which one I should choose. the first one has a low battery indicator, over-load protection and auto power off function. It will measure DC to 20A and voltage to 1000V, and AC to 20A and voltage to 700V. Resistance measurements to 20M ohm, and capacitance measurements from 2000pF to 20mF (MegaFarad?) . It measures frequency to 20kHz, and temperature from -50 to +1000 degrees C. includes protective holster and probes(non-autoranging.) the next one is a four digit autoranger and can measure DCV-Range-400mV, 4V, 40V, 400V, 1000V. ACV-Range-400mV, 4V, 40V, 400V, 750V. DC current-Range-400uA, 4mA, 40mA, 200mA, 10A. AC current- Range-400uA, 4mA, 40mA, 200mA, 10A. Resistance-Range-400 ohms, 4K ohms, 40K ohms, 400K ohms, 4M ohms, 40M ohms. Frequency counter-Range-40Hz, 400Hz, 4000Hz, 40KHz, 400KHz, 4MHz, 30MHz. Capacitance measurement-Range-4nF, 40nF, 400nF, 4uF, 40uF, 200uF. 2angle stand protective holster and probes.Which one would you get? Thanks, Mike

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Re: DMM Help

Post by russlk » Tue Nov 05, 2002 5:52 pm

Depends on price and what you need. I probably would not buy either one, based on price!

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Re: DMM Help

Post by greg123 » Tue Nov 05, 2002 6:06 pm

In my opinion:<p>-Low Battery is basically a standard, its found on even cheap $20 units.
-Auto Power off is good and so is overload protection.
-Auto ranging very important for 2 handed measurements.
Measuring the current is not to practical in boards as it requires you to "Break the Circuit"
I've never bought a meter on current specs alone, but i am into electronics and mA.
-Frequency and Temp is good if accurate.
-Safety is also good....good insulated NOT PLASTIC probes<p>Well in my opinion, buy the best you can for the money. Somthing that is autoranging, with highest possible range in Resistance, Capacitance and DC and AC Voltage. Its also a good idea to get one with a warranty and a seal of calibration. I just bought a new fluke meter for around $450.00 canadian and its great.<p>[ November 06, 2002: Message edited by: theman ]</p>

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Re: DMM Help

Post by Crowbar » Tue Nov 05, 2002 6:10 pm

Mainly the choice of a DMM should be safety and features, after all that comes price. For low level measurements you can use almost anything, only real consideration is degree of accuracy. For high level measurements in an industrial enviroment you want a Cat III rating with associated probes as you WILL be using it on at least 480 VAC or more.
Keep Prying...


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Re: DMM Help

Post by Dean Huster » Wed Nov 06, 2002 5:23 am

Mike, Crowbar makes the most important point on this subject. If you're into industrial electricity and intend to use the meter in high-energy circuits (e.g., 480v, 3-phase, etc.) it absolutely should be rated for Category III or Category IV (the newest one) operation. That fact will be imprinted on the back of the meter. And don't swallow the phrase, "Will meet Category III requirements" for that meter hasn't truly been certified. Using some non-certified imported meter, no matter what kind of voltage ranges it has, in such an application can jeopardize your life if you happen to forget to set it to the correct function before trying to measure high-energy voltage. They can literally explode in your hands.<p>Handheld meters made by the John Fluke Mfg. Co. meet that specification, hands down. In addition, Flukes are literally "bulletproof". But they're also more expensive than most others.<p>"mF" is millifarad, not megafarad.<p>It's neat to have a meter with gobs and gobs of functions and lots of digits in the display. But the more functions a meter has, the more compromises that must be made in the meter. Accuracy is usually the first to go. Does the accuracy support the display? In other words, an accuracy of 1% cannot reliably display on more than 2-1/2 digits; 0.1% is limited to 3-1/2 digits; 0.01% is limited to 4-1/2 digits. If there are more digits than can be supported by the basic DC meter accuracy, those extra digits are good only for indicating short-term changes in voltage and not for quantative measurement of a voltage. All manufacturers (and I do mean ALL) are guilty of overextending their display like this, especially when functions other than DCV are invoked.<p>If your basic DCV accuracy turns out to be 0.1%, which is really good for most imports, you'll find that your DCA accuracy will be just a little worse and your ACV accuracy will be a lot worse, usually around 0.5 to 1%, depending upon frequency. And that lesser accuracy compromises your display even more. Resistance measurements will be all over the place. Even the finest and most expensive of 2-terminal resistance measuring instruments will be downright awful once you go below 10 to 100 ohms, because contact and lead resistance become a significant part of the reading, and just subtracting that residual out doesn't guarantee full meter accuracy. It takes a 4-terminal measurement for those low values, so beware if that will be one of your primary measurements.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).


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