Clamp Meters

Ummm... What are you not agreeing with now? That an amp-probe will not give you a true reading? Isn't that what I just said? Let me expand that statement: Any magnetically coupled meter (wrap-around type) will not give you a true reading because (the important part-) they are magnetically cupped. As the frequency rises (square = sine plus every harmonic) the transfer ratio increases, producing more voltage in the secondary loop (same reason a 60 cps transformer is much bigger than a 400 cps transformer, like those used in plains.) and that RF broadcasting works.
The "true RMS" meters work well but are a far cry for accurate if they are magnetically cupped. To get an accurate reading, you must break the circuit, introduce a passive, frequency independent resistance, then monitor the drop across the resistor. Any magnetic involvement screws the equation as you have introduce an inductive element which will not be liner to frequency. To make matters worse, the type of waveform that is produced by a dimmer is part sign and part square, dividing at the chop point.
I must further state that amp-probe was not a term describing a brand of meter, but a type of meter, specifically a "non-intrusive clamp on meter." I am aware of the old style magnetically operated Amprobe" as a brand, but the spelling is different, which is why I spelled it out amp-probe.
My own current unit is this one- http://www.lashen.com/vendors/fluke/336.asp I would trust it to give me a good ballpark thermal load reading.

1. Any non-true-RMS meter will give you an inaccurate reading on a non-linear current waveform. The clamp-on current transformer has almost nothing to do with the inaccuracy.

2. Almost all field current measurement on AC line circuits are accomplished with clamp-on or toroidal current transformers, not by breaking the circuit and measuring across a resistance. That is just not practical in most cases.

3. Good true RMS clamp-on meters are capable of quite high accuracies even when presented with high-harmonic content waveforms. For example, the Fluke 345 clamp-on meter is capable of +/- 3% of reading on crest factors between 1.1 and 3, and +/- 5% of reading on crest factors between 3 and 5. This is pretty darned accurate.

4. Typical instruments have frequency response of 15 Hz to 1kHz for the meter and clamp-on transformer combination. The accuracies above are measured across that frequency range. This takes care of the instrument response to harmonic frequencies in no-sinusoidal waveforms like a phase-control dimmer.

The bottom line: magnetically coupling the meter to the conductor under measurement does not introduce gross inaccuracies, even when the waveform is harmonic-rich. Gross inaccuracies come from using a non-true-RMS instrument on a non-sinusoidal current waveform. That was the point I was originally trying to make.


ST
 
removing the outer insulation on a cable to expose te insulated conductors on a permament electrical installation is consider an unlawful modification in many jurisdictions. here in Ontario the individual who performs such an act is liable to be personally fined - likewise their employer can b e fined and they can be made to pay a victim surcharge plus pay for the repairs. A recent case resulted in a cable TV installer being fined $10,000 and his em^ployer was fined a similar amount. Fortunately no one was injured by this action of stripping away 1 inch of outer sleeving of a piece of Romx outside of an approved box.

To be honest when I read this post the questions that are being asked about the use of basic electrical test equipment indicate that the person doing this type of measurement should stop and find someone who is a competant (legal word here) to show them how to do this type of measurement safely. It is very easy to suffer serious second and third degree burns or lose your life by performing these types of measurements incorrectly (using the wrong setting and or euipment, slipping with a probe etc etc).

it is good to ask the questions and want to learn however the next step is to get someone to show you and take the training. Good luck.
 
The easiest, and possibly safest way to use your clamp on ammeter is to buy something like this. Sure, you spend a few extra bux, but in the end, your theatre probably already has edison to stage pin adapters. Then there is no need to construct your own electrical devices and no need for "creative" solutions to using your equipment. Did I mention it was safer?
 
The easiest, and possibly safest way to use your clamp on ammeter is to buy something like this. Sure, you spend a few extra bux, but in the end, your theatre probably already has edison to stage pin adapters. Then there is no need to construct your own electrical devices and no need for "creative" solutions to using your equipment. Did I mention it was safer?

Thank you, very much for finding that, I think that typa thing is just what I needed, though I need to try and find a 13A plug version, which I'm sure there'll be somewhere on the internet. Thanks for the find.
 
While that's a nice item icewolf08, do I really need to buy something, for $14.99 US, that I already have the parts for, AND since our original poster, Diarmuid, is UK-based, he would need to build TWO adapters to use it? EDIT-answered by the post above, for the most part. Diarmuid , do you see the Edison, NEMA 5-15, PBU, plug and connector in the UK, often?


STEVETERRY, as I am a (sometimes) House Electrician of an arena, are you suggesting I should throw away my Fluke 30 and purchase a Fluke 345 (or equivalent) for $1395.00 US?! Yikes. Would a Fluke 334A, for $164.95 US, be acceptable?

Has my Fluke 30 really been giving me inaccurate readings of ETC Sensor™ Touring Racks all these years? Does the level of the dimmers matter (as to the amount of inaccuracy)? [I usually take a reading with ALL Dimmers at Full before the show, and sometimes a couple of readings during the show, if I suspect the load is approaching 400a/leg, on that particular service.]
 
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While that's a nice item icewolf08, do I really need to buy something, for $14.99 US, that I already have the parts for, AND since our original poster, Diarmuid, is UK-based, he would need to build TWO adapters to use it? EDIT-answered by the post above, for the most part. Diarmuid , do you see the Edison, NEMA 5-15, PBU, plug and connector in the UK, often?
STEVETERRY, as I am a (sometimes) House Electrician of an arena, are you suggesting I should throw away my Fluke 30 and purchase a Fluke 345 (or equivalent) for $1395.00 US?! Yikes. Would a Fluke 334A, for $164.95 US, be acceptable?
Has my Fluke 30 really been giving me inaccurate readings of ETC Sensor™ Touring Racks all these years? Does the level of the dimmers matter (as to the amount of inaccuracy)? [I usually take a reading with ALL Dimmers at Full before the show, and sometimes a couple of readings during the show, if I suspect the load is approaching 400a/leg, on that particular service.]

Your Fluke 30 meter, while a fine tool, is the wrong meter for the job in that it's not a true-RMS device. In the same price range, the Fluke 32 is the ticket, or equivalent. Your readings have been "close", since you test with all dimmers at full, where the current waveform is almost a sine-wave. Had you wanted to measure the current in the neutral with all dimmers at half (a useful test), you would have gotten much more inaccurate (low) readings.

I was using the specs on the more-accurate Fluke 345 simply to make the point that current transformer clamps are not inherently inaccurate, as a previous post suggested.

As for the line splitter--Icewolf08 is right--it's the right tool for the job. It preserves the 600V insulation rating of the cable and it's UL-Listed. If I had remembered these devices, I would have suggested them earlier. Thanks, Alex!


ST
 
Your Fluke 30 meter, while a fine tool, is the wrong meter for the job in that it's not a true-RMS device. In the same price range, the Fluke 32 is the ticket, or equivalent. Your readings have been "close", since you test with all dimmers at full, where the current waveform is almost a sine-wave. Had you wanted to measure the current in the neutral with all dimmers at half (a useful test), you would have gotten much more inaccurate (low) readings....
Watch ebay soon for a Fluke 30 meter, in very good condition, and still have the original box. Ordering a Fluke 32 (or equivalent) now. Thank you, Mr. Terry. There goes my Xmas money.:)
 
1. Any non-true-RMS meter will give you an inaccurate reading on a non-linear current waveform. The clamp-on current transformer has almost nothing to do with the inaccuracy.

Actually, it has everything to do with the inaccuracy. An inductor by nature (of which transformers are, and that is what you really are using in a clamp on meter) is frequency dependant. (see below)

2. Almost all field current measurement on AC line circuits are accomplished with clamp-on or toroidal current transformers, not by breaking the circuit and measuring across a resistance. That is just not practical in most cases.

In no case am I suggesting you break the line in field application. My referral is to lab measurements. Most all electric company meters (that I've ever seen) do indeed measure by use of a torad, with the exception of domestic meters.

3. Good true RMS clamp-on meters are capable of quite high accuracies even when presented with high-harmonic content waveforms. For example, the Fluke 345 clamp-on meter is capable of +/- 3% of reading on crest factors between 1.1 and 3, and +/- 5% of reading on crest factors between 3 and 5. This is pretty darned accurate.

I am not arguing this point. see below.

4. Typical instruments have frequency response of 15 Hz to 1kHz for the meter and clamp-on transformer combination. The accuracies above are measured across that frequency range. This takes care of the instrument response to harmonic frequencies in no-sinusoidal waveforms like a phase-control dimmer.

And there in lies the problem! The output from a dimmer is not one frequency. If has a low frequency element (60cps) but also has high frequency harmonics all the way up to whatever filtering limit is on the dimmer! I am sure at any given frequency, your meter is accurate. The problem is the nature of taking multiple readings at multiple frequencies at the same time.

The bottom line: magnetically coupling the meter to the conductor under measurement does not introduce gross inaccuracies, even when the waveform is harmonic-rich. Gross inaccuracies come from using a non-true-RMS instrument on a non-sinusoidal current waveform. That was the point I was originally trying to make.

And this is what is confusing me. I never said otherwise! I am perfectly happy using the meter I am using. :)
 
Watch ebay soon for a Fluke 30 meter, in very good condition, and still have the original box. Ordering a Fluke 32 (or equivalent) now. Thank you, Mr. Terry. There goes my Xmas money.:)


I just looked up the 334, and it has the same problem--it's not true-RMS.

Cheers

ST
 
In an earlier post, you said:

"Let me expand that statement: Any magnetically coupled meter (wrap-around type) will not give you a true reading because (the important part-) they are magnetically cupped. As the frequency rises (square = sine plus every harmonic) the transfer ratio increases, producing more voltage in the secondary loop (same reason a 60 cps transformer is much bigger than a 400 cps transformer, like those used in plains.) and that RF broadcasting works."

True-RMS meters with good crest factors get around this problem. They are designed to measure non-sinusoidal waveforms with high harmonic content while preserving true-RMS accuracy. That includes those types with clamp-on current transformers.

ST
 
It was once upon the big boss’s visiting a show site that there was a wee problem in balancing the load, and further discovered that not one of the crew possessed a clamp meter so as to help solve or diagnose the problem. It was than mandated into corporate rule that any employee that wished to do shows should possess a clamp meter. Ya’ know how simple could that be, I even had one while a carpenter by trade...

Given this mandate which has a bit fallen to the wayside in requirement level until next time by way of active memory in what could happen... I set out as the shop tool person to find and study the clamp meter at the same time as my B&K clamp meter was starting to give me problems or limited for what I needed.

Did a study of the following:
Model # Brand True RMS AC Amps DC Amps AC Voltage DC Voltage Resistance Capacitance Continuity Temperature Frequency Peak/Hold Jaw Size


Of this there were a few defining features important. First the seperation of True RMS that on a computer dimmer will counter the non-wattage effect, and jaw size - a 4/0 type SC feeder cable has a specific diamater and those clamp meters that will not fit over the cable won’t work so well. Add to that amperage rating of 400A and less, features such as peak hold and max hold, ability to test voltage both AC and DC, frequency, resistance and have a beep for it, etc. and you have what will be an all around multi-meter. Add to this some Fluke add on/replacable jaws to one’s probes and you have a really useful multi-meter. As long as bananna clip style probe as another limitation. Beyond this was accuracy and features available.

Below is what I studied and the starting prices from 2003: (given this is a Word Perfect table and it does not translate so well to the net.... Perhaps print if really interested in what I found in this study of most brands of clamp meter.)

SEE PDF posted below...



Since than, those of the upper tier of people such as me bought the best Ideal (above Fluke) in spec choice for clamp meter. While we had to get used to it taking a bit longer to settle down in zeroing, for the most part it is a good easy to use true RMS meter. Those stating out seem in the other extreme of budget most often settle for non-tru RMS meters of the Extech brand and there is nothing really wrong with them. Accuracy, RMS and features are at times less but for the price they work well. For those following the rule, it is a good meter even if the jaws are a bit small in just able to fit the cable. While one co-worker was waiting for the Ideal clamp meter simillar to mine was waiting for the thing to just settle down and zero out he sent me an E-Mail about the thing... What is this crap you specified over Fluke... it won’t zero. Did a study of my own and it does take it’s own time in zeroing, but on the other hand is much more cost effective, accurate and more important yet does offer more features than the Fluke line of product. I was really disappointed in what Fluke for clamp meters had to offer. This not to say that Fluke and other brands don’t have a place, just that for the best, at times it is not Fluke. I did the best and they also have full warranty in one lens breaking under use and it being replaced.

Still beyond clamp meters there is multi-meters that measure amperage. One can even test such a thing thru a figure eight with one’s probes. Bought thru McMaster Carr a Extec multi-meter non-clamp meter or two now that will meter thru the probes 20 amps and that’s sufficient and necessary to test a follow spot.. Master ballast testing prociedure for a Lycian 924 ballast is with a multi-meter that tests up to 20 amps by way of probes into the multi-pin plug. Far different than testing 400A range on a show this testing with the probes the multi-pin plug to ensure it will as a ballast provide the proper amperage. At minimum at work now, I now have two types of amperage meters and ones that the common standard to the industry Fluke #77 won’t do. One to do feeder cable in the 400A range, plus is true RMS and very accurate, one that tests ballasts, than one that is analog. Something not mentioned above is the analog meter.

In an expert in the induststry coming to visit where I work in giving a class, he requested a meter. Gave him mine, it was not sufficient. Gave him the shop’s old analog meter and he was satified. Why would one choose an analog meter over a digital meter? Analog meters have a sort of resistance that compensates for computers, computer meters I learn don’t. Going for a clamp meter... go with the best or go simply analog I learn as often even better yet. The old timers use analog clamp meters if they use them - they often don’t in already having solved problems, but non the less it is their magic. Yet to buy one but it is on my own shopping list such an analog clamp meter. No... Not such a thing as a Radio Shack type meter in considering it accurate, more like a Spherry type brand and one well respected.

Still the expert in the industry recognized my meter and did his thing given it’s limitations and slowness to zero. True RMS and not True he explained etc. in teaching how to use such a meter. Beyond buying a multi-meter, this much less just as if multi-meter, one that beyond what the multi-meter does, one that will also tell amps about a cable, one needs physical instruction in how to use it. This much less at least a knowledge of what “True RMS” is or its use for our purposes where appropriate or in need or necessity dependant upon the person using it.

Multi-meters are a science, beyond this are clamp meters that do what a multi-meter will do yet go beyond that. Cannot imagine the need for say a Fluke #77 these days when a clamp meter will do what it did in our world plus more.

It’s possible that if one buys a good enough multi-meter, one can also buy the accessory amp clam for it and it’s going to work the same, but one needs to buy a good meter in the first place, than invest further into it. Cannot see any rational in a plug in feature that does the same as a meter that alredy does it however.

On Fluke on the other hand, Fluke #TL 223... It’s a sort of probe type accessories kit that will work with most brands of quality banana plug type mult-meter and has a number of probes that disconnect and reconnect. Great idea - others have similar but not as good. Add onto it with other styles of clip and you now have ease in testing stuff. Clip the alligator clip onto one pin and probe with the other. This as opposed to attempting to hold a probe on one pin and test to another without much ease.

Me, I’m an Ideal meter person in having replaced my discontinued B&K clamp meter that I loved and was great. Hz, amps AC and DC amps and volts, ohms and continuity. Add to this True RMS, ability to clamp the cable, peak and max hold, than after those options accuracy and you now have a great multi-meter for our industry.
 
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For GE 4552 and 4559s, there's no ceramic, so I've had to write on the glass, but that burns/wears off over time. Every place I've worked seems to have had a mixture of 4552 and 4559, never on the same bar, of course.:)
ship and len are probably too young to remember HiLights, a major R&R company of the '70s and '80s. I bought all their PAR lamps when they finally folded. They had engraved "HLI" in the back of every lamp, with an electric engraver. Taking it a tad too far, if you ask me.

Yep too young.. besides I'm not a rock and roller by hart and a carpenter by trade.... yea.. that worked out well for me these days in the end. Yes, I stock 547 different types of lamp having just done my year 2007 $250,000+ inventory for lamps. Major headache in trying to make the Word Perfect table preform as if Excell so as to make sumtotals but I did do so - screw Excell.

I know $4552 lamps and $4559 lamps, don't have the latter in stock though I wish I did so as to see. Len on the other hand... them might be fighting words with him.

Still engraving HLI on the back of the lamps. Could be brilliant or could be really stupid in weakening the glass. Paint marker for the glass and graphite for the porcelain works for me - this and yelling at my vendors that supply inks that wear off.
 
Major headache in trying to make the Word Perfect table preform as if Excell so as to make sumtotals but I did do so - screw Excell.

I know $4552 lamps and $4559 lamps, don't have the latter in stock though I wish I did so as to see. Len on the other hand... them might be fighting words with him.
Hey, ship, do you have the ability to generate a .pdf document from Word Perfect, or Excel for that matter? Your posting is just gibberish due to the lack of formatting, and a PDF would solve that. Also, could you not have exported your WordPerfect document to Excel to do the calculations? Both are easy on a Mac, someone else will have to explain how to do it under Windows.

The 600w ACLs are brighter enough for me to overlook the (perceived, in my opinion) lag in response time due to the larger filament. Len, which do you prefer, and why?
 
Here is the rest of the 2002/2003 list of tools at one point I worked up as useful. This in attempt to post a PDF by way of experiment.
 

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Hey ship - if you have any of the information in tables, you can use a program called PDF Creator. Free program. Basically, you just install it as a printer, and then you just print like you would to any hard copy printer - but it will just print it as a PDF to a file. I find alot of the posts useful, but if you already have the information in a table, that would be even more useful! I use this all the time when sending "official" stuff, so that none of the original formatting gets lost, and PDF is basically the standard file format for finalized text document transfers.
 
ship, that is a fantastic tool list. I'm starting a new thread in the "general advice" forum with that as the "flagship", no pun intended.
 
I may have missed it, there's so much good info in this thread, But did someone post the solution to the main question yet ? The trick with a clamp on amp-probe is to build a little jummper. Edison male on one end female on the other. connect everything together with 10-12 gauge single wires. thnn, or just the inside conductors from a standard cable. Plug the device you are checking into the female end and the male end into the wall, dimmer etc. This adapter allows you to clamp onto just one conuctor at a time. I have several of these in my tool kit with varying gauges of wire, and connectors. Obviously you don't need an adapter if you are chaecking the legs of feeder cable, but it's good to have a four wire setup and a couple of three wire set-ups. Remember when making the adapters, and using them, to use a properly rated connector and wire gauge e.g. don't use a 16ga wire on something you think might have 20 amps running through it, that would be bad.
 
My concern was that this query is from a school student in a country with 240/440 volt system.
basically if you don't know how to work a clamp meter it is probably irresponsible for this site to try and explain, already we have seen talk about stripping off insulation and I know what is meant but if someone gets the wrong idea.........
Sorry to be a kill joy, I usually as irresponsible as the next man but I have a bad vibe about making these suggestions to someone with a clamp meter at school.
 

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