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Posted by David Sherman on Tuesday, February 17, 2009 at 22:31:03 :
In Reply to: speaking of digital posted by copey on Tuesday, February 17, 2009 at 14:50:59 :
None of my cheap digital voltmeters will work even for just measuring the battery voltage on a vehicle with a mechanical voltage regulator. The farther you get away from the battery, the worse it gets. The sparking of the points in the regulator causes too much electrical noise. Sometimes they're so sensitive that the electrical noise actually drives the microprocessor nuts and you have to reboot it to get it to work. However, my Fluke meters always work fine in that situation.
Do you have a Fluke meter or an off-brand one? I used to work for Fluke, and I know they really do build them better than the cheapo meters. They not only add better noise filtering and shielding (the military versions meet TEMPEST emi/rfi/emp specs), but they also have displays designed not to blow up in your face if you accidentally put the leads across a high-voltage wire, and they have an extra 600 volt fuse in series with the usual 2 amp fuse on the current range. That's because if you have the meter in amps mode and accidentally put the leads across a 600 volt industrial power bus, the little 2 amp fuse will vaporize, coat the inside of the glass tube with condensed metal vapor, and become a dead short. When that happens, a cheapo meter will go up in smoke, but with a Fluke meter, it'll just blow the 3 amp 600 volt fuse with no damage to you or the meter.
I keep $3 Harbor Freight meters stuffed into every tool box and shed, because the cheap meter you have on hand is better than the good one that's back at the shop, but if you want the voltmeter equivalent of a Snap-On wrench, spend the $100 on a Fluke. Fluke invented the hand held digital voltmeter (well, actually Norm Strong did), and they know how to make them survive real world working conditions.