Measruement range for Amps for portable Multimeters - Page 1
Forum section: electronics / general

author: Hans Gebert
author_rank: Contributor
timestamp: January 16, 2013, 08:24:38 am
content: Hey all,most Multimeters out there have different inputs for uA-measurements and measuremet above (10A).I just wondered if the 10A option is really needed. 70mA can kill within milliseconds..So when I know that there will be currents above serveral mA I usually use my Clamp-Meter. How about you? Do you use the 10A option or is it just there but never used?Sincerely,Hans

author: rr100
author_rank: Frequent Contributor
timestamp: January 16, 2013, 08:35:19 am
content: Take a look around you, many things use 1-10A.What kills you doesn't matter, you can use real probes (with wires) not your fingers.

author: Hans Gebert
author_rank: Contributor
timestamp: January 16, 2013, 09:26:43 am
content: examples? I know that there are a lot of things using 1-10A..but nevertheless..nearly always its possible to measure with a clamp..perhaps i just haven't encountered the applications where current measurement in row is a must

author: Harvs
author_rank: Super Contributor
timestamp: January 16, 2013, 09:30:00 am
content: Dc current. It doesn't have to be mains voltage to use a dmm... I rarely use my meter for anything above 50v, just because that's not what I work with. In fact I use external shunts to get higher currents often.

author: Achilles
author_rank: Regular Contributor
timestamp: January 16, 2013, 09:37:29 am
content: Well, split in two parts here I guess. If you're just into some electronics you're fine with an mA Range. I often needed the 10A range to check solar powered setups, so I don't want to miss that one.Otherwise, you could use a transducer clamp for Amps (like the Metrahit Base) does, but that means more investment and something else to carry around. A meter without an 10A mode won't wander into my toolbag.....EDIT:My work is set-up and maintenance of research equipment in Meteorology/Climatology and remote sensing. So partly R&D and Electrician

author: Hans Gebert
author_rank: Contributor
timestamp: January 16, 2013, 09:41:01 am
content: Could you guys write down in which field you are working?Examples R&D, HVAC, Electrician...that would help to understand if I miss anything..

author: jnd
author_rank: Regular Contributor
timestamp: January 16, 2013, 10:18:03 am
content: For most of my measurements in low voltage electronics I need mA and A up to few amps. We got two the Agilent U1232A at work and when I compared them to the Fluke 117s which we have I was initially amazed by the number of features and noticed even the uA range. However there is no mA range! Microamps or amps, nothing in between...Fo some hobby project uA can be nice but I don't need it at work and what I was really missing from the Fluke 117 was the milliamps. I mean, even the cheapest meters have mA ranges, why not these? Are they trying to justify their higher models with this?I agree that clamp meters are nice for fast current measurement however they're not that precise. We have one good PROVA model which can measure down to 400 mA DC range but these aren't cheap. One good thing is they don't have burden voltage. Which is another bad thing on the U1232A, you get about 300 mV per 100 uA which means nearly 2 V on full scale of 600 uA

author: ejeffrey
author_rank: Super Contributor
timestamp: January 16, 2013, 06:20:44 pm
content: Quote from: Hans Gebert on January 16, 2013, 08:24:38 am70 milliamps at 120 volts can kill. Not so much at 10 volts that many of us prefer to work. The current is there, but there simply isn't enough voltage to push it through your body.Likewise, a 5 milliamp circuit at 120 volt is not something you should consider safe by any means. Just because it only consumes 5 milliamp doesn't mean that the power supply can't drive 100 milliamp through your body.

author: SeanB
author_rank: Super Contributor
timestamp: January 16, 2013, 06:44:36 pm
content: Measuring AC current I almost never use the 10a range on a meter, I use a clamp meter, mostly because in my case most of the measurements are over 10A, up to 200A. Mostly I use it on motors and to balance phase loads.For Dc I will use the built in meter, as I do not currently have an AC/DC current probe ( but have not missed it too much for DC) and am looking for one cheap.

author: rr100
author_rank: Frequent Contributor
timestamp: January 16, 2013, 07:32:18 pm
content: Quote from: Hans Gebert on January 16, 2013, 09:26:43 amLaptop, desktop, a few phones, most/all tablets, a decent torch or battery charger, some digital cameras. And probably many more.Sometimes you can use a clamp meter for such things but more often than not you just don't get the precision you need. And I'm talking about VERY rough estimates. A crap 10 or 20A multimeter even with 2000 counts can read (if it has autoranging on that scale, most do): 15 mA or 147 mA or 1135 mA or 5.15 A or 15.24 A. When you read 2.1A on a good clamp meter you get at least a rough estimate, but how about when the device goes to sleep and you read 0.1A on the clamp meter? It can be in fact 15mA or 200mA. Or even zero! You can't just go with a multimeter on 200mA scale and see what's going on; apart from being inconvenient the device might wake up and go 1.5A and blow your fuse. And you also get a much higher voltage drop on the miliampermeter.

author: Hans Gebert
author_rank: Contributor
timestamp: January 17, 2013, 08:28:15 am
content: that sounds for me like..we need a multimeter that has the 10A Range + protection but can measure everything on this range..from uA, mA to A...does something like this exist?

author: Achilles
author_rank: Regular Contributor
timestamp: January 17, 2013, 09:15:13 am
content: I think the Metrix MTX-328x Series has just one Amps socket which is used for all.Martin reviewed it once and is pretty happy with that fellow. The only thing I dislike is the clamshell design, otherwise it has really interesting features (one Amps socket, simultaneous A and V measurement, Math functions, graphical display, logging with timestamp, RTD temperature measurement)

author: Hans Gebert
author_rank: Contributor
timestamp: January 18, 2013, 07:08:11 am
content: The Mextrix device you mentioned seems pretty decent. It's pretty much what I searched for..you just can't misplace your probes in die A, uA, mA or V jacks. Thats an huge advantage..nevertheless the design is really ugly..Edit: Votes without comments are half the fun

author: Hans Gebert
author_rank: Contributor
timestamp: January 18, 2013, 08:22:13 am
content: One more question that came just up to me:Is there a meter with a good battery concept? Means the battery recharges when measuring voltage? Does something like this exist or can it even be realised?

author: Harvs
author_rank: Super Contributor
timestamp: January 18, 2013, 08:53:26 am
content: Quote from: Hans Gebert on January 18, 2013, 08:22:13 amThe answer depends on what you mean. If you're talking about recharging its own batteries off a voltage source it's measuring, then no. The ideal multimeter has an infinite input impedance on the voltage ranges and an input imp of zero on current, so as not to effect whatever it's measuring. What that means is you have zero input power to harvest.If you're talking about recharging off a plug-pack, well yes you could, just like the fluke 196B scopemeter. However it adds a lot of complication (which translates to cost) because it all needs to be isolated. The second thing is the typical DMM can last quite a long time on a few AAs, so it's not going to be worth it.

author: Unknown
author_rank: Unknown
timestamp: January 18, 2013, 08:56:24 am
content: That meter would draw current from the circuit. It would have a very low input impedance and influence the circuit. It would be a really bad idea in all but a very limited set of circumstances. To charge an AA cell at 0.01C, it would require about 40 mW. This number would probably have to be even higher, since the average meter only spends a small amount of its time being connected to a voltage source. At 5 V, this 40 mW draw would represent an impedance of about 600 ohm. Measuring in digital circuits might easily introduce a 10+% error. Measuring in high-impedance circuits (eg. audio amplifiers with ~10kOhm input impedance) will be impossible.I can also see fun stuff happening in mains circuits. You measure between live and earth. The meter draws just enough current to trip the GFCI/ELCB. That might make for one unhappy customer.The Agilent U1253 OLED meter has a battery that can be recharged via a special power supply connected to the input jacks.

author: Achilles
author_rank: Regular Contributor
timestamp: January 18, 2013, 10:00:01 am
content: Quote from: alm on January 18, 2013, 08:56:24 amwell, it's not special....just a 24V DC source. You can also charge it with your lab powersupply set at 24V and plugging in 4mm Bananas in the GND and mA Jack. That 24V supply from the U1253B is pretty bulky, so most times I don't use it as a normal powersupply is on the table anyway.You can only charge it when it's turned off, otherwise you'll blow the fuse.Gossen Metrawatt has some Metrahit meters which have a DC jack. I have the same jack on my GMC calibrator. The manual states it won't charge, but power the meter. The Metrahit E Extra and Metrahit Energy uses that supply as well.

author: Hans Gebert
author_rank: Contributor
timestamp: January 21, 2013, 02:50:38 pm
content: Some times has passed and I had time to watch Martins review concerning the Mextrix MTX-328x-Series.Well it's not exactly the ideal device in my opinion..why does it have two 3 jacks..common, A and V...Why is there no meheter with just two jacks so you can't put your probes into the false input. That woulde be really great..never change the inputs..just select the function and..measure..I know it has someting to do with the internal architecuture of today's multimeters but well..couldn't this be changed somehow?!

author: SeanB
author_rank: Super Contributor
timestamp: January 21, 2013, 03:38:38 pm
content: More to do with the cost of the switches. A switch that can both handle 10A, 1000v and at the same time not add extra contact resistance while handling millivolt signals is expensive, as well as not something which will be available in a mutipole rotary configuration. 3 sockets are a lot cheaper.

author: c4757p
author_rank: Super Contributor
timestamp: January 21, 2013, 03:44:21 pm
content: Also, and more importantly IMHO, is that with separate jacks, if you switch modes with the probes attached, you usually won't blow anything (everything but the current modes is usually pretty robust). One accidental brush past A or mA with a single input and you pop your fuse or worse.

author: Hans Gebert
author_rank: Contributor
timestamp: January 21, 2013, 04:00:25 pm
content: Well haven't so much fear about this one..Nowadays there are power electronics which could reduce if not prevent such accidents/blow ups.But I understand the cost thing..rotary switch could stay but only for the selection of the function..not like now to change the circuits...alibi switch for all the guys used to it :E

author: rsjsouza
author_rank: Super Contributor
timestamp: January 21, 2013, 04:01:28 pm
content: Quote from: Hans Gebert on January 16, 2013, 09:26:43 amSure there are...Even a simple AA battery gives a lot of current if connected to a small load, therefore the best practice is always to start on the high current range and then reduce to smaller levels. This is good practice when the current is unknown or can reach higher levels unexpectedly - examples would be tracking defects on equipment or if a short occurs when debugging a new project.Quote from: Hans Gebert on January 17, 2013, 08:28:15 amIf you look at several of the older DMMs (Fluke 8020, for example), everything was integrated into the same input: from 200uA to 2A (Fluke 8060 is 10A). However, more modern DMMs with auto-range have the current inputs split between mA and A ranges because it is easier and simpler to maintain accuracy at the lowest ranges.

author: PA4TIM
author_rank: Super Contributor
timestamp: January 21, 2013, 04:09:39 pm
content: If I use a meter to measure current it is pA to uA. Most times things like leakage. I have a pA meter and a spotgalvanometer for this sort of things. Sondtimes I use my Keithley or prema for this,I allmost never use a multimeter for measuring higher current. I have an old fluke 8000 with 20 A option. This one I used one time adjusting the ampmeter of a battery charger/tester/dynamic load i designed.For the rest i measure the voltdrop over a resistor allready in a circuit or I use a Tek P6042 AC/DC currentprobe, a clampmeter or a seperate shunt.I think mistakes made in current measurenent is multimeter dead cause number one. ( the cheap not protected that are not fused in 10A and let you switch to voltage while the bananas are still in current busses

author: rr100
author_rank: Frequent Contributor
timestamp: January 21, 2013, 05:41:42 pm
content: Quote from: Hans Gebert on January 21, 2013, 02:50:38 pmSome time has passed and I ordered the "beastie". With 3 wires you can do VandA at the same time (yes, that's power, usually). And you can alsologit! Big selling point.Also even without dual function still for protection is best to have different wires. If you use the same wires it's just too easy to mess up your circuit by changing something on the meter and grounding by mistake whatever point you want to measure.Quote from: Hans Gebert on January 21, 2013, 04:00:25 pmThe electronics might protect your meter but not the circuit you try to measure.

author: Hans Gebert
author_rank: Contributor
timestamp: January 22, 2013, 01:10:59 pm
content: if it would be such a big prob for security..how can it be that for example fluke 116 measures Voltage and uA with only two jacks...no switching needed :Eif it works for small currents there has to be a possbility to do the same for larger currents..

author: Unknown
author_rank: Unknown
timestamp: January 22, 2013, 06:43:40 pm
content: The shunt for the uA range will have a much larger value than the shunt for the 10 A range, so the damage from putting it across your circuit will be much less. Switch design is also much easier. This is why it's very common for the mA and uA range to share the same input socket, but sharing mA and A is not so common.

author: Slothie
author_rank: Regular Contributor
timestamp: January 23, 2013, 12:24:08 am
content: Don't be afraid of electricity! If you're working on voltages of 50v or less (as most of us are most of the time) its virtually impossible to get a shock or kill yourself (I'm told licking the top of a PP3 is painful, but I've never been stupid enough to try it!). I guess if you impaled yourself with some electrodes near the heart and attached 50v to it you might kill yourself, but if you're doing that then you have more problems than the risk of electric shock!You can get burns if your skin is too near when you short out a high current source, so its worth being careful with high power battery packs (NiCd, LiPo etc) but if you are reasonably cautious then you've really nothing to worry about, aside from damaging expensive equipment.High voltages and Mains are a different matter, and you should assume that they are "live" or capacitors fully charged until you have proven positively to yourself they are not.If you're using a multimeter with insulated probes and you know what you are trying to measure then you are perfectly safe. I've done a LOT of mains work (250v and 400v AC) and have never received a shock using a multimeter on live wiring because I take my time and make sure I use good quality probes and wear gloves when reaching through chassis to get to the point I'm measuring!

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 23, 2013, 02:55:43 am
content: Up to a few A would be good for direct measurement. Above that, insertion resistance can cause significant measurement errors in low voltage circuits and a Hall effect current probe would be more suitable.

author: Hans Gebert
author_rank: Contributor
timestamp: January 23, 2013, 02:35:11 pm
content: @rr100: the specs of the metrix mtx say that I starts measuring volts by 0,1V..and amps by 1mA....Thats pretty shitty isn't it? Don't u have problems with these ranges?

author: rsjsouza
author_rank: Super Contributor
timestamp: January 23, 2013, 03:11:37 pm
content: Quote from: Slothie on January 23, 2013, 12:24:08 amTry licking the top of a 9V battery. It is shocking. I did it when I was a child (6 or 7) convinced by my older cousins this would only cause a tickle...

author: G7PSK
author_rank: Super Contributor
timestamp: January 23, 2013, 04:01:47 pm
content: Quote from: rsjsouza on January 23, 2013, 03:11:37 pmI would not describe the feeling of 9 volts on the tongue as painful, certainly not comfortable and most certainly distasteful, leaves a nasty acidic come metallic taste on the tongue for a short while, not some thing I would do for kicks but I often check PP3 batteries this way if I think that they may be bad and I don,t have meter to hand, I can tell from the size of the buzz approximately what state the battery is in.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 23, 2013, 04:35:21 pm
content: Quote from: G7PSK on January 23, 2013, 04:01:47 pmYou are probably right on your description of the sensation... At six years old, I wasn't so sophisticated or versed in words to describe it...

author: rr100
author_rank: Frequent Contributor
timestamp: January 23, 2013, 07:52:34 pm
content: Quote from: Hans Gebert on January 23, 2013, 02:35:11 pmYou're reading it wrong or you have really unreasonable expectations. The lowest ranges are 0.1V and 1mA and being 100 000 counts it means it has 1uV and 10nA resolution. That is 100 times better on V and 10 times better on A than Fluke 83V/87V. That is not to say it's 100 times better than the Fluke. In particular the contrast is shockingly bad, I was thinking it's my unit (it's a second hand) but from youtube it looks bad in some cases so it might be a general problem (for exampleat around 15:20).But in any case the autoranging over whole V and A domain is really nice.

author: nanofrog
author_rank: Super Contributor
timestamp: January 24, 2013, 03:57:58 am
content: Whether or not a uA range is needed would depend on what you're doing IMHO. Personally, I like having it, even if I don't need it very often.As per greater than 1A (10A based on the poll selections), I see this as necessary, as even a wall wort can exceed 1A current output (amongst other examples others have posted).

author: Hans Gebert
author_rank: Contributor
timestamp: January 24, 2013, 04:23:37 pm
content: @rr100: means there is no problem in measuring flame sensing diodes?Fluke 17X series starts with 5mA range if I read the specs correctly..6000 Counts...means 5uA would be shown as : 0,005mA ??Not really useful for flame sensing.. or am I totally wrong? (It's late..-.-)

author: rr100
author_rank: Frequent Contributor
timestamp: January 24, 2013, 07:49:52 pm
content: The numbers sound right but I've no idea what the flame sensing diodes do, if they need some nA scale, if you need to capture some singular events, etc.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 24, 2013, 07:57:20 pm
content: Quote from: Hans Gebert on January 24, 2013, 04:23:37 pmAccording to its manual, the 17x series (175, 177, 179) has 6000 counts and the lowest range is 60mA - which gives a resolution of 10uA...