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Old 19-06-2013, 20:18   #76
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Re: Multimeters - What Features To Look For.

How to measure current and power -* using a hall effect transducer - clamp

for you home brew types
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Old 19-06-2013, 20:55   #77
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Re: Multimeters - What Features To Look For.

Foggy-
"Hall" isn't a brand. The "Hall Effect" is the physical interplay between a magnetic field and a Hall Effect Semiconductor, much the same as the way light causes a reaction in a solar panel. It allows for much more sensitive reading of magnetic fields than a simple magnetic induction coil would.

And yes, shunts are expensive. The $4 shunt from China looks like a piece of scrap iron next to a typical $25 US shunt. I wouldn't bet on how well it ages in salt air or how well it has been calibrated, thermally compensated, etc. Bought a cheap Shenzhen digital meter to see what I'd get, and the plastic in front of the LEDs warped from room heat within a week. They were also unreadable in sunlight. (Large green display.)
If the $4 job works good enough for you...great. I can buy a foot of power cable for less and use it the same way.
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Old 05-09-2013, 17:00   #78
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Re: Multimeters - What Features To Look For.

I'm going to offer MHO, and while some of you may disagree with it, it's based on 30 yrs of hands-on electronics background (10 yrs Navy sub ET, 11 yrs defense contractor and 9 yrs self employed.)

As a defense contractor, all of our test equipment was required to be calibrated at the Navy's cal lab. Most of my coworkers used Fluke 77s, one guy bought a Fluke 87 and I bought a Centech which had all of the same features as the 87, but IIRC, it was only $35 instead of $350. We sent them in to cal and mine came back calibrated, his $350 Fluke 87 could not be calibrated - brand new, right out of the box. Of course he returned it, and got another one which passed cal. I still use the $35 one occasionally, but I usually use the $3.99 Cen Techs from HF. Why? Because they're so cheap, if one gets broken, no big deal. Plus for the last 9 yrs, I've had no requirement to have a calibrated DMM, so the cheap ones do what I need them to. Most of the time, someone asks me to help them diagnose a problem with their RV, and they don't own a meter or know how to use one. I bring over a $4 meter, I show them how to use it, diagnose the problem, help them fix it (if we don't need parts from town), drink a couple of beers and give them the DMM. I keep them around like chewing gum. One in each vehicle, 3 or 4 in the trailer to give away, a couple in the house.

I just compared one of my $4 DMM to the calibrated meter using a NiZn battery. The calibrated meter registered 1.563 VDC. The $4 meter registered 1.565 VDC. So the cheapo meter was off by .002 V on the 2 volt scale. I don't think 2 millivolts is going to mislead any DIY guy tracking down 120v or 12v.


Why do I mention this? Because many of us (and I still do this a lot) equate more expensive with higher quality. But often, there isn't a direct correlation between price and quality. The only way to tell the quality of a DMM is to either do some research on electronics hobbyist websites (let someone else buy one and open it up) or take a chance and buy one that you think might be good. My search today indicates it looks like my meter was pretty popular in it's day, but is no longer in production. The current model number is Mastech M9508, which is also hard to find.

I'm not saying that every $4 DMM is as good or as accurate as a Fluke, but I am stating this: after using and passing out probably 15 - 20 of the cheapo DMMs, I never saw one that appeared to be off by more than .01v on the DCV scale. At the same time, spending almost $400 for a Fluke 87-V will buy you an uncalibrated meter. You'll have to order and pay extra for calibration.

I don't currently own a boat, but I am fairly familiar with Murphy's law which I believe is very closely related. One of the more obscure corollaries of Murphy's Law is:
The probability of a piece of test equipment (or repair parts) falling into the bilge or getting knocked over the side into the water rises exponentially with the cost of the test equipment or part. In accordance with that, even though the $4 units are cheap, they'll probably never go away - like the proverbial ex-wife who claims you still owe her child support.

What I'd suggest is buy a couple of the cheapo DMMs for every day use. If it breaks or gets wet, no big loss. Then as others have suggested, pick up a good quality True RMS DMM for $150 or less (Agilent, BK Precision, Mastech, and others look pretty good) and a good quality clamp on ammeter (like the Mastech MS2108 I just got on Ebay for $61) and tie a string around both so they don't go in the water. This way if you ever need the added accuracy and/or precision, you have it.

Sometimes (actually all of the time), the talent of the technician or handyman is far more important in troubleshooting success than the price of his test equipment.
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Old 05-09-2013, 18:40   #79
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Re: Multimeters - What Features To Look For.

Quote:
Originally Posted by socaldmax View Post
I'm going to offer MHO, and while some of you may disagree with it, it's based on 30 yrs of hands-on electronics background (10 yrs Navy sub ET, 11 yrs defense contractor and 9 yrs self employed.)

As a defense contractor, all of our test equipment was required to be calibrated at the Navy's cal lab. Most of my coworkers used Fluke 77s, one guy bought a Fluke 87 and I bought a Centech which had all of the same features as the 87, but IIRC, it was only $35 instead of $350. We sent them in to cal and mine came back calibrated, his $350 Fluke 87 could not be calibrated - brand new, right out of the box. Of course he returned it, and got another one which passed cal. I still use the $35 one occasionally, but I usually use the $3.99 Cen Techs from HF. Why? Because they're so cheap, if one gets broken, no big deal. Plus for the last 9 yrs, I've had no requirement to have a calibrated DMM, so the cheap ones do what I need them to. Most of the time, someone asks me to help them diagnose a problem with their RV, and they don't own a meter or know how to use one. I bring over a $4 meter, I show them how to use it, diagnose the problem, help them fix it (if we don't need parts from town), drink a couple of beers and give them the DMM. I keep them around like chewing gum. One in each vehicle, 3 or 4 in the trailer to give away, a couple in the house.

I just compared one of my $4 DMM to the calibrated meter using a NiZn battery. The calibrated meter registered 1.563 VDC. The $4 meter registered 1.565 VDC. So the cheapo meter was off by .002 V on the 2 volt scale. I don't think 2 millivolts is going to mislead any DIY guy tracking down 120v or 12v.


Why do I mention this? Because many of us (and I still do this a lot) equate more expensive with higher quality. But often, there isn't a direct correlation between price and quality. The only way to tell the quality of a DMM is to either do some research on electronics hobbyist websites (let someone else buy one and open it up) or take a chance and buy one that you think might be good. My search today indicates it looks like my meter was pretty popular in it's day, but is no longer in production. The current model number is Mastech M9508, which is also hard to find.

I'm not saying that every $4 DMM is as good or as accurate as a Fluke, but I am stating this: after using and passing out probably 15 - 20 of the cheapo DMMs, I never saw one that appeared to be off by more than .01v on the DCV scale. At the same time, spending almost $400 for a Fluke 87-V will buy you an uncalibrated meter. You'll have to order and pay extra for calibration.

I don't currently own a boat, but I am fairly familiar with Murphy's law which I believe is very closely related. One of the more obscure corollaries of Murphy's Law is:
The probability of a piece of test equipment (or repair parts) falling into the bilge or getting knocked over the side into the water rises exponentially with the cost of the test equipment or part. In accordance with that, even though the $4 units are cheap, they'll probably never go away - like the proverbial ex-wife who claims you still owe her child support.

What I'd suggest is buy a couple of the cheapo DMMs for every day use. If it breaks or gets wet, no big loss. Then as others have suggested, pick up a good quality True RMS DMM for $150 or less (Agilent, BK Precision, Mastech, and others look pretty good) and a good quality clamp on ammeter (like the Mastech MS2108 I just got on Ebay for $61) and tie a string around both so they don't go in the water. This way if you ever need the added accuracy and/or precision, you have it.

Sometimes (actually all of the time), the talent of the technician or handyman is far more important in troubleshooting success than the price of his test equipment.
Thanks for your input.
I put the Mastech on my wish list.
Where are the $4.00 meters?
I want a couple for the boys.
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Old 05-09-2013, 19:26   #80
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Re: Multimeters - What Features To Look For.

If you watch the Horror Fright magazine ads, sometimes they are literally giving away the $5 or $10 multimeters. I picked one up that way figuring I can keep it in the car and if it gets stolen, I'm not out a lot of money.

Also got around to testing it versus a calibration source, which put out 10.00 VDC precisely. And compared to my other meters...the HF meter was about as close as a test light. I've never seen one so far off, including one that was ten years old and had a good chance to age and drift before it ever got tested.

Maybe I just got the winner, like the bad Fluke. But as a test light, it works just fine. It will never earn my trust as the "go to" meter though.
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Old 05-09-2013, 19:33   #81
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Re: Multimeters - What Features To Look For.

Quite often Harbor Freight has their Cen Tech 7 function DMM for sale for $3.99. When I need some, I just stock up on a few more. A lot of stuff that HF sells is junk (especially their LED flashlights), some of it is OK - consumable items like grinding disks are OK. I've found that by really looking closely at whatever the tool or item is, I can pretty much tell the decent quality items from the junk. If you don't like it, they'll always take it back.
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Old 05-09-2013, 19:46   #82
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Re: Multimeters - What Features To Look For.

Quote:
Originally Posted by hellosailor View Post
If you watch the Horror Fright magazine ads, sometimes they are literally giving away the $5 or $10 multimeters. I picked one up that way figuring I can keep it in the car and if it gets stolen, I'm not out a lot of money.

Also got around to testing it versus a calibration source, which put out 10.00 VDC precisely. And compared to my other meters...the HF meter was about as close as a test light. I've never seen one so far off, including one that was ten years old and had a good chance to age and drift before it ever got tested.

Maybe I just got the winner, like the bad Fluke. But as a test light, it works just fine. It will never earn my trust as the "go to" meter though.


Here's a good example of someone having the opposite experience I did. Not that I think any of the HF DMMs are calibrated, but they're only $4, not $400.
I look at them as consumables, and they're good enough to tell me if an alternator is charging, or if there is a bad connection.

They're so cheap, it's almost not even worth the gas to drive back to HF to exchange for another one, unless you have several or other items to take back. For important measurements, one should have a true RMS DMM, I just think you can find plenty of good ones in the sub $100 or $150 range.
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Old 06-09-2013, 10:56   #83
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Re: Multimeters - What Features To Look For.

I work on vintage vacuum tube amplifiers alot. Over the years I have tried a couple of cheap VOM's. Radio Shack & another hardware store one. Both were severely off in some ranges of V and Milliamps. I have a small Fluke that I bought in '88. It is still going strong. Frankly I dont think you need an expensive meter for a boat.... most of what you are measuring is DCV. But how to know if it's any good to start with?
I put a $5 Digital voltmeter on my boat recently with a STDP switch to be able to check each batterys voltage. Works great and is right on with t he Fluke reading. Go figure....
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Old 08-09-2013, 18:47   #84
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Re: Multimeters - What Features To Look For.

Can someone please tell me what the difference is between these two is????

They look the same to me......


Amazon.com: Mastech MS2108 True-RMS AC/DC Clamp Meter with Inrush Current Measurement: Home Improvement

Amazon.com: professional MS2108 AC DC Current Clamp Meter backlight Frq Cap CATIII vs FLUKE hol: Home Improvement

On 84.00 the other 39.00. If it is a fluke (forgive me please) I would like to take advantage of it before it changes.

Thanks much.
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Old 08-09-2013, 19:09   #85
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Re: Multimeters - What Features To Look For.

New MASTECH MS2108A 400 AC DC Current Clamp Meter - Amazon.com

Looks like all three are the same, this one at $43 including free Prime shipping.
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Old 08-09-2013, 19:20   #86
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Re: Multimeters - What Features To Look For.

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Originally Posted by hellosailor View Post
New MASTECH MS2108A 400 AC DC Current Clamp Meter - Amazon.com

Looks like all three are the same, this one at $43 including free Prime shipping.
But what does the "A" mean?
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Old 08-09-2013, 19:30   #87
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Re: Multimeters - What Features To Look For.

MS2108/2108A AC DC Current Voltage Clamp Meter Backlight Frq CATIII vs FLUKE Hol Large Jaw 26 mm 6600 Counts 600V, View Clamp Meter, MASTECH Product Details from Shenzhen Youfu Tools Co., Ltd. on Alibaba.com

Appears to be all the same from our friends in Shenzhen.

The "professional" listing on Amazon says 2108, but shows 2108A in their picture as well.

Looks like the "A" model may be newer with 60/660ADC range instead of 40/400ADC
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Old 08-09-2013, 19:31   #88
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Re: Multimeters - What Features To Look For.

I found it.

True RMS

http://www.p-mastech.com/index.php?p...mart&Itemid=29

http://www.p-mastech.com/index.php?p...mart&Itemid=29
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Old 08-09-2013, 19:34   #89
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Re: Multimeters - What Features To Look For.

Yep.

That is it.

Amazon.com: professional MS2108 AC DC Current Clamp Meter backlight Frq Cap CATIII vs FLUKE hol: Home Improvement
says it is a 2108 but the pic shows a A model.

The true 2108 has "T-RMS" just above and the left of the screen.

Tricky stuff.

Still, what you get is what you pay for eh?
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Old 08-09-2013, 20:11   #90
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Re: Multimeters - What Features To Look For.

Yup, the vendor selling the "MS2108" for $39.95 left the "A" off the end. Maybe accidental, but I'm guessing it wasn't.

I did buy an MS2108 on Ebay for $61. It will take another week for it to arrive.
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