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post #11 of 15 Old 12-29-2009
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Originally Posted by Maine Sail View Post
Edited: I see Ed beat me to the EX-830 recommendation...
Great minds...

If you know what features that you are looking for, I believe that there are some good deals to be had through eBay.

I wanted: a DC clamp-type multimeter for measuring charging current,
a True RMS meter for accurately measuring AC.

The fact that the Extech has a built in IR Thermometer, and a thermocouple thermometer was a bonus. Note that the IR thermometer does not have a very narrow sensing beam (it's 8:1). On some of the handheld IR thermometers it's more often 12:1.

- Ed
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post #12 of 15 Old 12-29-2009
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I recommend Circuit Specialists Inc.. My company buys a lot of our lab equipment from them; they have good prices and a selection ranging from 'disposable' to 'lab quality'. Heck, if you spend over $50, they'll even throw in a cheap DMM for free: Circuit Specialists Inc. - Promotional Special
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post #13 of 15 Old 12-30-2009
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I recommend Circuit Specialists Inc.. My company buys a lot of our lab equipment from them; they have good prices and a selection ranging from 'disposable' to 'lab quality'. Heck, if you spend over $50, they'll even throw in a cheap DMM for free: Circuit Specialists Inc. - Promotional Special
Note that the meter from circuit specialists is NOT a true RMS (root mean squared - it is a way of representing the statistical amplitude of a sine wave) meter. That's why the stated value of the meter is only $25


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post #14 of 15 Old 12-30-2009
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Okay, here is a useful trick for you guys with clamp-on amp meters. If they don't have a low amp range of say 10 amps or so they are pretty much useless for measuring current of fractional hp motors. A lot of these digital clamp-ons have specs like +- 3% FS on a 100 amp range. That 3% of FULL SCALE. So trying to measure a motor that is supposed to draw 10 amps you could read anywhere from 7 amps to 13 amps!

Had this happen at a jobsite a little while ago on a 1 hp 3 phase 480 volt pump that was tripping out. The electrician says he amped it out and it is only pulling 1.2 amps, no problem it's rated 1.3 amps. I didn't believe his meter. I had him wind a ten turn coil of wire with the motor current running through it. Then put the ten turns in the clamp-on. He reads 23 amps now, and divides the reading by 10, to get 2.3 amps. Ahha! the motor is seriously overloaded!

I install these ten turn coils between the contactor and the overload block on all motors that draw less than about 10 amps. I always demonstrate the error to people, and they are always amazed at the magnitude of the error.

In the days of mercury thermostats with 'heat anticipators' I used to carry a 100 turn coild made of bell wire. I'd insert it in the thermostat circuit so my 6 amp clamp-on would read down to 60 milliamps.
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post #15 of 15 Old 01-27-2010 Thread Starter
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Okay, here is a useful trick for you guys with clamp-on amp meters. If they don't have a low amp range of say 10 amps or so they are pretty much useless for measuring current of fractional hp motors.
Sounds like a cool trick but sadly I can't visualize the details. Would you mind explaining or better yet showing a picture or two.
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