Author Topic: Low Current DC Clamp Meter  (Read 25414 times)

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Offline Mike WarrenTopic starter

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Low Current DC Clamp Meter
« on: July 03, 2015, 10:31:17 pm »
More and more often we are needing to measure the standby battery current in cars with everything shut down.

This used to be a rare occurrence, so the inconvenience of disconnecting the battery wasn't an issue, but with the increasing use of electronic accessories in cars now days we have to do it more often. This is complicated on modern cars as many of them will draw well over an amp when the battery is first connected, which means the person doing it needs to make sure the meter is shorted out for a few seconds on initial connection. Mistakes are made and multimeter fuses get blown.

I thought I'd see if anyone knew of a cheapish clamp meter that will measure DC current with at least 10mA resolution (preferably 1mA) and will fit over a car battery cable, which might be up to 13mm or so. Accuracy is not particularly important. It would take the job from minutes down to seconds.

I haven't used a clamp meter for many years, and that was only on reasonably high current AC.

 

Offline retiredcaps

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Re: Low Current DC Clamp Meter
« Reply #1 on: July 04, 2015, 01:29:52 am »
No idea if this is any good or meets the car requirements, but saw this thread earlier when it got bumped.

https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/
 

Offline Stray Electron

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Re: Low Current DC Clamp Meter
« Reply #2 on: July 04, 2015, 02:01:00 am »
   I frequently troubleshoot automotive wiring by looking at and tracing the current flow. It's a MUCH better way of troubleshooting some problems, such as mysteriously draining batteries, than by trying to look at voltages.  What I do is to find a junction that I can break AND that I can also that I can connect amp meter probes to something on each side of. I connect the amp meter probes  BEFORE I break the connection and then break the circuit. That way I never lose power to the automobile's circuits.  After I'm done checking, I reconnect the junction, then remove the amp meter and I don't have to reset the alarm, the clock, the radio code, stations, etc etc.

   One place that I can usually break a junction is at the battery. I can't reliably connect to most battery posts so that's out but frequently the wires connecting to the various major devices are bolted to the battery clamp so I can connect one side of my amp meter to the battery clamp and the other to the wire. After the meter is set and connected, just unbolt that one wire and start reading.

    If there's no place to connect the amp meter to on the battery side I have resorted to having a helper push a probe against the top of the battery post and holding it there while I unbolt the clamp and slide it off of the post (thus breaking the circuit). I then have the helper hold the clamp above the battery post and with the insulated probe sticking through the clamp.  As long as they can hold everything in place, you're go to go! Obviously this is only good for checks that you can make quickly. But if you need more time they can just slide the clamp back on the battery post and take a break while you figure out what to do next.

   PS:  To avoid the possibility of shorting the battery, it's better to connect the amp meter in the return (aka ground) circuit instead of the "hot" side whenever possible. That way if you accidentally short something to ground there's little if any voltage difference and no current flow. 
 

Offline PTR_1275

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Re: Low Current DC Clamp Meter
« Reply #3 on: July 04, 2015, 02:06:55 am »
Hi Mike,

I know Altronics do one. I've had my eye on it for a while for the same reason. Never tried it so can't say the quality / accuracy but their gear is normally pretty good. The jaw might be a bit on the small side for big cables.

http://www.altronics.com.au/p/q0968-compact-acdc-clamp-meter/
 

Offline Mike WarrenTopic starter

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Re: Low Current DC Clamp Meter
« Reply #4 on: July 04, 2015, 02:37:29 am »
Thanks for the replies.

That Altronics one looks perfect, especially since we have a wholesale account with them and order regularly. I did look at it briefly, but missed the 4A range. Not sure how, since it's clearly written twice.

I'll order one on Monday.

 

Offline PTR_1275

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Re: Low Current DC Clamp Meter
« Reply #5 on: July 04, 2015, 02:44:07 am »
Brilliant. Let me know how it goes and I might be persuaded to buy one as well.
 

Offline Lightages

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Re: Low Current DC Clamp Meter
« Reply #6 on: July 04, 2015, 03:24:51 am »
 

Offline mtdoc

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Re: Low Current DC Clamp Meter
« Reply #7 on: July 04, 2015, 04:34:38 am »
I bought one of THESE GTC branded meters a few years ago and am very happy with it. Martin Lorton did a review some time ago ( see below)  As I recall it has decent accuracy in the millivolt range. I can't recall the exact specs but I did check it when I first got it and it was within those.

It may be a rebrand of the cheaper ones above though it looks somewhat different. For one thing it's a right handed meter.... :-+

« Last Edit: July 04, 2015, 04:39:39 am by mtdoc »
 

Offline Someone

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Re: Low Current DC Clamp Meter
« Reply #8 on: July 04, 2015, 08:16:05 am »
Clamps tend to wander around with their offset quite a bit, and can be a bit trying to use around the low end of their rating. Is a clamp a 100% requirement? You mention blowing fuses on meters, where a Fluke 87 has 1mA resolution to 6A and 10mA resolution up to the full 10A with a 20A surge rating. The high resolution and min/max/average modes are great for working on power systems.
 

Offline HackedFridgeMagnet

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Re: Low Current DC Clamp Meter
« Reply #9 on: July 04, 2015, 08:21:28 am »
Frankie sold me one similar to those.
Seems ok, but doesn't like the 1.2 volt NiMh rechargeable batteries.
 

Offline BravoV

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Re: Low Current DC Clamp Meter
« Reply #10 on: July 04, 2015, 08:26:32 am »
Clamps tend to wander around with their offset quite a bit, and can be a bit trying to use around the low end of their rating.

Agreed, especially for clamp type measurement, a stable reading for DC low current within mA resolution is tricky.

I own Agilent U1213A clamp meter, the specification for DC current at 40 Amp range is with resolution of 10 mA, but the reality that its useable resolution only at 100 mA.

As the earth magnet it self can affect the sensor, cause just by waving the meter at the air at different orientation, the offset can jump within +/- 20 to 50 mA.  ::)

Turning or waving the clamp orientation at nearby huge metal object like big metal drawer or machinery can affect DC amp reading even worst.
« Last Edit: July 04, 2015, 08:30:19 am by BravoV »
 

Offline nctnico

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Re: Low Current DC Clamp Meter
« Reply #11 on: July 04, 2015, 09:06:13 am »
When tracing low currents in a car it is better to disconnect the batter (the minus) and put a multimeter in series. Just don't turn over the starter or turn on the lights.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline 0xdeadbeef

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Re: Low Current DC Clamp Meter
« Reply #12 on: July 04, 2015, 09:06:41 am »
The Metrawatt Gossen meters (at least the X-TRA) can measure from 100µa to 10A (16A for short duration) via a single connector jack and a single fuse.
https://www.gossenmetrawatt.com/english/produkte/metrahitx-tra.htm
Note very cheap though. Offcial price (including VAT) is close to 600€.
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Offline HighVoltage

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Re: Low Current DC Clamp Meter
« Reply #13 on: July 04, 2015, 11:44:50 am »
Hi Mike,

I know Altronics do one. I've had my eye on it for a while for the same reason. Never tried it so can't say the quality / accuracy but their gear is normally pretty good. The jaw might be a bit on the small side for big cables.

http://www.altronics.com.au/p/q0968-compact-acdc-clamp-meter/
That indeed is a very good looking clamp meter with 1mA resolution.
Is this Altronics brand specific to Australia?
It seems they are not offering international sales.
Where would one buy one of these in Europe?




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Offline Mike WarrenTopic starter

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Re: Low Current DC Clamp Meter
« Reply #14 on: July 04, 2015, 12:18:34 pm »
Is a clamp a 100% requirement? You mention blowing fuses on meters, where a Fluke 87 has 1mA resolution to 6A and 10mA resolution up to the full 10A with a 20A surge rating. The high resolution and min/max/average modes are great for working on power systems.

The important thing is for the unskilled people using this to quickly get a feel for if the vehicle is drawing more than about 50mA or so. At the moment they are so scared of blowing up meters that they call me from my work to do the test for them. And it's getting more regular.

Since this meter is so cheap, it's worth giving it a go.

I did think about making a device with a small shunt and a couple of solid alligator clips that could be clamped between the battery negative terminal and its cable and then they could just use a meter on mV, but the speed of a clamp has a lot going for it. If the meter fails, I'll build the adaptor.
 

Offline Mike WarrenTopic starter

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Re: Low Current DC Clamp Meter
« Reply #15 on: July 04, 2015, 12:20:38 pm »
The Metrawatt Gossen meters (at least the X-TRA) can measure from 100µa to 10A (16A for short duration) via a single connector jack and a single fuse.
https://www.gossenmetrawatt.com/english/produkte/metrahitx-tra.htm
Note very cheap though. Offcial price (including VAT) is close to 600€.

I shudder to think of how that would be treated in our installation bays. :)
 

Offline Mike WarrenTopic starter

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Re: Low Current DC Clamp Meter
« Reply #16 on: July 04, 2015, 12:27:14 pm »
Is this Altronics brand specific to Australia?

Yes, but they just re-brand Chinese stuff.

Quote
Where would one buy one of these in Europe?

Lightages posted a link to what looks like the same meter on ebay:
http://www.ebay.com/itm/DT337-AC-DC-Measurement-Mini-Digital-Clamp-Meter-Tester-Multimeter-for-CEM-/171741076657?pt=LH_DefaultDomain_0&hash=item27fc90dcb1
 

Offline 0xdeadbeef

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Re: Low Current DC Clamp Meter
« Reply #17 on: July 04, 2015, 12:28:10 pm »
That indeed is a very good looking clamp meter with 1mA resolution.
Is this Altronics brand specific to Australia?
It seems they are not offering international sales.
Where would one buy one of these in Europe?
As noted above, this is most probably a rebadge of some Chinese meter.
Despite of the different buttons and the flipped design (if this isn't just the image), I would assume this Voltcraft rebadge is exactly the same thing.
http://www.voelkner.de/products/501606/VOLTCRAFT-Stromzange-Hand-Multimeter-digital-VC-539-CAT-III-600-V-Anzeige-Counts-4000.html

Maybe an alternative for Europeans:
http://www.voelkner.de/products/210/Benning-Stromzange-cm-2-AC-DC.html
« Last Edit: July 04, 2015, 12:33:13 pm by 0xdeadbeef »
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Offline HighVoltage

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Re: Low Current DC Clamp Meter
« Reply #18 on: July 04, 2015, 12:52:43 pm »
Very interesting.
I found the re-branded Voltcraft VC-539 about 10 km away from me in a Conrad store.
Thanks for all your suggestions, I will get the probe next week and test it out in the mA range.
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Offline Rupunzell

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Re: Low Current DC Clamp Meter
« Reply #19 on: July 04, 2015, 02:55:55 pm »
The classic clamp on DC current meter was the hewlett packard 428 (1958) the 428B (1961). It is a flux gate magnetometer based current meter. The 428B version had a full scale range of 1mA to 10A. Range sensitivity can be increased by adding a loop or loops of the wire carrying the current to be measured around the current probe aperture. Or splitting the current by using one or more wires to carry the current to be measured.

Notable in the hp 428B, at the 3mA and 1mA full scale current range, there is an adjustment to compensate for the earth's magnetic field. If this compensation is not done, measured current accuracy is affected.

There is a large aperture probe for higher currents and a magnetometer probe for measurement of magnetic fields.
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1961-11.pdf

Yes, is fire bottle based and work really well in good condition. Fire bottles are not a reliability or service life liability.

When hp discontinued the 428B after decades of production, Applied Physics purchased the design and produces two version of this clip on current meter to this day, 428C and 428D along with a portable version 428P. These Applied Physics current meters are fully compatible with the all hp current probes made for the 428.
http://appliedphysics.com/products/products/



Bernice
 
 

Offline 0xdeadbeef

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Re: Low Current DC Clamp Meter
« Reply #20 on: July 04, 2015, 06:32:12 pm »
For the sake of completeness, for ~300€ (incl. VAT) Benning offers the CM 11 which has a 300mA DC range with a 0.1mA resolution (±1%+10 Digit)
http://www.benning-shop24.de/stromzangen-benning-cm-11-044067-p-784.html

BTW: why prefer the VC-539 over the Uni-T UT210E? Well, Uni-T doesn't have the best reputation, but at least the manufacturer is clear. Besides, the input protection looks better, it's True-RMS, has better (claimed) accuracy in the lowest DC ampere range (±2%+3 digits vs. ±4%+10 digits) and costs half of the VC-539...
Trying is the first step towards failure - Homer J. Simpson
 

Offline korlatos

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Re: Low Current DC Clamp Meter
« Reply #21 on: July 05, 2015, 02:45:25 am »
AEMC K100 provides 1mV/mA output signal and can measure from 100uA to 4.5A DC.

http://www.testequipmentdepot.com/AEMC/accessories/current-measurement-probes/ac-dc-microprobes/k100.htm
 

Offline korlatos

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Re: Low Current DC Clamp Meter
« Reply #22 on: July 05, 2015, 02:58:55 am »
AEMC K100 provides 1mV/mA output signal and can measure from 100uA to 4.5A DC.

http://www.testequipmentdepot.com/AEMC/accessories/current-measurement-probes/ac-dc-microprobes/k100.htm

BTW, K100 uses flux gate magnetometer technology, just like HP 428B.

http://www.aemc.com/products/html/view.asp?id=204&dbname=products
 

Online nowlan

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Re: Low Current DC Clamp Meter
« Reply #23 on: July 05, 2015, 04:26:55 am »

Review: CEM DT-337 milliamp clamp meter
http://www.cem-instruments.com/en/pro/pro-519.html
 

Offline 0xdeadbeef

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Re: Low Current DC Clamp Meter
« Reply #24 on: July 05, 2015, 06:49:02 am »
I stumbled over another mA clamp meter made by company called Prova from Taiwan
http://www.wisoft.com.tw/prova/jsp/provafront/prova.jsp?lang=en#

The Prova 11 (TrueRMS) claims ±1.5% +5dgts in the DC mA range (0-4A).
Pretty expensive though (230€-300€) for an unknown brand and a little hard to come by.

There's also a probe version of this called Prova 15.

[Edit]
The Prova 11 is obviously also rebranded as Extech 380942
« Last Edit: July 06, 2015, 07:26:11 pm by 0xdeadbeef »
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