|Topic Review (Newest First)|
|01-27-2010 10:20 PM|
Originally Posted by GaryHLucas View Post
|12-30-2009 11:31 PM|
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.
|12-30-2009 10:41 PM|
Originally Posted by Selkie60 View Post
|12-29-2009 02:27 PM|
|Selkie60||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|
|12-29-2009 01:16 PM|
Originally Posted by Maine Sail View Post
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.
|12-29-2009 10:34 AM|
I own the Mastech 2108 and discovered that it is not as accurate or fast for measuring DC in-rush as I would prefer. For all other features it is spot on and a great value. When I bough this it was to replace a Fluke that I had loaned to my dad for over a year. The day I got it back I dropped it out of my pocket from the dinghy and into the water. Ouch!!!! Should have left it with my dad a little longer..
The Fluke 337 will accurately measure DC in-rush but the Mastech 2108 is not as fast. It works ok for AC in-rush but I do not believe it captures peaks as well as my old Fluke did for DC in-rush.
I do plan to buy another Fluke but have not been in a huge rush for these very short duration peaks as they have not been a huge priority recently. The Mastech has proven to be a decent meter though. For the price, the 2108 is an good value and a surprisingly durable meter. My only complaint other than the DC in-rush (does AC in-rush fine) is the size of the display numbers, too small..
I believe Extech makes a clamp that will do DC inrush that is as fast as the Fluke so you may want to check them out as well. I also own a UEI meter, though not clamp, and that meter has been beat on for years and years and still keeps ticking...
If you find a good deal on a Fluke 337 let me know, I need a new one. I still recommend the 2108, with the DC in-rush caveat and the small display peeve..
If I had to do it again though, for an in-expensive DC clamp, I might try the Extech EX 830 1000A AC/DC clamp, it has a built in infrared thermometer and will capture DC peaks greater than 1ms in duration (about $210.00) or the EX-730 which is an 800A AC/DC clamp that also captures DC peaks greater than 1ms and costs about $160.00.
Edited: I see Ed beat me to the EX-830 recommendation...
|12-29-2009 10:31 AM|
I have an Extech EX830 Clamp Multimeter
It measures: AC/DC Current,
Temperature with an Infrared probe
Diode and Continuity test
Peak function captures inrush currents and voltage transients
True RMS Current and Voltage measurements
I got it on Fleaybay for about $120
|12-29-2009 09:10 AM|
Mastech is a Chinese electronics manufacturer. They turn out some pretty good stuff. I have had their 20A 0-50VDC power supply (HY5020E) for two years, and find it very well made. Based on this, I would expect their other products to be pretty good, too.
The meter you're looking at has some very desirable features, which many less expensive meters don't. Among these are: In-rush Current measurement and Clamp-on Frequency measurement -- both are very useful for working around generators, electric motors, etc.
I have top-of-the line Fluke meters (Fluke 189 and Fluke 337), but the Mastech meters at about half the price of the Flukes would probably be good values for medium-duty service.
For really cheap multimeters, I prefer the Velleman....can be had for under $20. Handsome, rugged, functional. I open them up, adjust them to read in the 12V range exactly the values measured by my Fluke 189, and give them to my clients! Every boat should have an accurate multimeter aboard :-)
|12-29-2009 07:23 AM|
I just bought a fluke from ebay a few months back. I got a fantastic deal too, the meter was in new condition for a great price.
Before I bought anything I researched like crazy (for about three months) for the features I wanted in a multimeter then I looked all over for the best deal which happened to be ebay.
UEI is supposed to be a good meter but not good as fluke.
|12-29-2009 05:27 AM|
|tager||I would either go for the fluke or the $30 special. Anything in between is a waste of money.|
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