EEVBLOG #75 - Digital Multimeters

[Kiriakos-GR]

I'm happy for you, K.  Give us your review as you have time.  It looks in very good shape, practically new.
You're old DMM seems to be quite well used, a testament also to its durability.

Note, for safety the lightning annunciator to warn you about the shock potential of the V you have on.

Thanks Mate for your positive spirit  

I will write few words about my feelings, for the Newcomer ..

The first quirk found on it , was at the temperature setting, the inner sensor in order to work ,
needs from your end , to have leads crossed ( in contact ) ...  thats stupid ... but understandable .
It does not have an separate K-Prob input , so it needs my help to react properly.
With out the leads crossed the screen reads  { OPEn  }  ( circuit )    

The holster , with the extended rear ( foot - leg - support point ) , does not look to be well designed ,
it causes the feeling that the instrument will fall - flip , by an accidental sock , or even by pooling the test leads  in your direction.
( I am working on a solution about it , I had not made my mind yet )  
 
Check this picture..



Another  quirk that I found , are the clear plastic on the  display ,
its so shiny that causes  reflections  " glare " , even with the indoor lighting.  
( An not shinny LCD protector film , could be the answer )

Another  quirk
At High Resolution mode ...  at 20V (end of the high resolution road )
The meter correctly show as { 19.999 } above that drops to { 20.10 },that is logical.
In order to show again the high Resolution , it does not need to lower the voltage to less than 20 again , but to drop it down to 16.80 ... then it shows again High resolution .  Why ? .. why why ? tight asses  
( My DC PSU has an 30 turns potentiometer on it ... I have to do 3-4  complete rotations to drop it that low !! )
.
.
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Other than that , the instrument looks solid ... Thanks God  


Few posts above I had speak about the inner Fuses, quick acting ones.  
And I just feel the need to explain my view - opinion - conclusion .

a)  About the Fuse ratings , the higher Fuse ratting , will force the manufacturer ,
to make one equal rated  PCB design and electronics .... So the MetraWatt must be better made than Fluke, so to survive in such an incident .

b)  Fuse rating - Max breaking capacity in KA  or thousands of Ampere ....
We need some one more expert , to tell us whats going on here ..
By combining scattered info .. like ..
1) The 87 Fluke can do 20A at 20 secs at 1KV  
2) Fluke recently updated the fuse rating from 17KA to 20KA ( 20.000A) ( 11A one)
3) The word capacity =  Amperes + time =  keep alive seconds
By combining all those , the MetraWatt should doing if I am not mistaken ,
as 20A for 30 seconds Max !!  
So its  33.3% more powerful in this area .    
  
c) We should not " force " the people , to throw away good tools , just from fear ,
that could " possibly "  blow - explode  ....  I recommencement to all who haves such instruments ,
to get an pair of " fusible probes " ... simple - effective - cheap.

d) Common glass fuses , does not explode , never did .
The car industry uses those for years .
Still , by replacing your old fuses , with " quick active ones " ( those with grey body instead of glass ),
its an clever or smart thing to do ,  those  modern - better - fuses , are probably used on the fusible probes too.

e) One last notice about multimeter 's  with slots and openings on the front panel.
Those are totally " in door " designs ... moisture or liquids are the enemy here .
One little opening on the multimeter , its not possible to be an enemy.

But for out door usage ... there are high risks ,  but this haves to worry mostly the industrial electricians,
that they " have to " work in all weather conditions,  &  also use  "open type toolboxes" ,
or if the environment that they work , are full of steams - heat or what ever other factor ,
that could raise the humidity level sky high , and could transform one simple multimeter ,
in to a wet stick ...  

Yes there is special gloves - boots - cloths ,
but electricity uses always the most direct path to meet you .  

About my old and brave one  
I had never removed the protective cheap nylon from the face plate ,
but even so , looks and works great .  

Dave.. I started reading your theory about the " burden voltage " .
Interesting stuff - for advanced tasks.  ( but lets stay on topic)        

 
 

[Kiriakos-GR]

Maybe the picture is making it look Black.

Check this link .. http://www.auctiva.com/hostedimages/showimage.aspx?gid=238574&image=359992571&images=359992571,359992649,359992608,359992632,359992866,359992847,359992737,359992754,359992703,359992721,359992666,359992777,359992889,359992796,359992587,359992827,359992810,359992995,359992978,359992950,359992911,359992932&formats=0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0&format=0

Its my multimeter , pictures are taken by the eBay seller.

[andri]

That meter is frigg'n hilarious!

I happen to own a multimeter that is probably a close relative to the one in that picture. (And no, I wouldn't call myself a proud owner). I got it a couple of years ago when I needed something that resembles a multimeter to take some quick measurements and they
were dirt cheap (in the 10€ range) at my local electronics store.

As people here tend to like multimeter porn, I opened it up and snapped a couple of pics (sorry for the distortion, I was using my mobile phone):




Given how Dave likes to talk about the importance of proper input design, it makes you really wonder how they justified slapping the "HIGH SAFETY" label on this one.

[Kiriakos-GR]

As people here tend to like multimeter porn, I opened it up and snapped a couple of pics (sorry for the distortion, I was using my mobile phone):

Good one  

it makes you really wonder how they justified slapping the "HIGH SAFETY" label on this one.

andri welcome , your name sounds to be from France .

Any way , no , I would be proud of your multimeter , if its going to be used at it named rating.
That is  500V ... This is what you had pay for , and get .

Those  " burned examples " , was tested .. OR  better said .. " blasted" , with an minimum of  1300 Volts.

The CAT III 1000 , its the nominal  not the maximum ,  the maximum should be 20-30% above that.  
Or even more ...

[EEVblog]

d) Common glass fuses , does not explode , never did .
The car industry uses those for years .
Still , by replacing your old fuses , with " quick active ones " ( those with grey body instead of glass ),
its an clever or smart thing to do ,  those  modern - better - fuses , are probably used on the fusible probes too.

Sorry, but you are off-the-mark and incorrect. Please go look up what HRC fuses are designed for, there are very good reasons why they exist and are used in multimeters and other equipment.
Standard glass fuses can only interrupt say an order of magnitude more than their rated current. Any higher and they may arc over, which means the fuse will continue to pass the current and it and other components can violently explode as a result.

It's not uncommon to find glass scattered all over your gear when glass fuses explode due to gross overloads.

Dave.

[Kiriakos-GR]

Sorry, but you are off-the-mark and incorrect. Please go look up what HRC fuses are designed for, there are very good reasons why they exist and are used in multimeters and other equipment.
Standard glass fuses can only interrupt say an order of magnitude more than their rated current. Any higher and they may arc over, which means the fuse will continue to pass the current and it and other components can violently explode as a result.

It's not uncommon to find glass scattered all over your gear when glass fuses explode due to gross overloads.

Dave.

Hi Dave .... arc over = some thousands of volts .
We can search and find  at what specific voltage rate,
the electricity can arc over the distance of 11 mm of the classic small fuses, or the distance of 19mm,
of the large Fast acting ones .

What we will never find, are totally fool proof multimeters .    

[PetrosA]

CAT ratings are explained here:

http://digital.ni.com/public.nsf/allkb/05D3F9C0F740BC2986256E9A00505421

The dangers that CAT ratings protect against are voltage spikes. Good multimeters will also be designed to minimize the likelihood of the meter becoming the source of an arc flash (which is one of the main reasons for using the HRC fuses). Most residential circuit breakers in N. America and Europe can withstand 10,000 amperes which is the most common available fault current from the transformers used by utilities. A meter has to be able to deal safely with that much fault current (and more) moving through it in the event of a voltage spike. This article gives an example of the dangers posed by a cheap multimeter on a common voltage:

http://ecmweb.com/ops_maintenance/defective-test-equipment-20100101/

As the first link shows, any outlet you test within 30'/10m of the point of origin of your electric service will be either CAT III or CAT IV and CAT II is only where you are at least 30'/10m from a CAT III source. So in most single family homes and in many apartments there may not be any CAT II outlets in the building which means you couldn't SAFELY use a CAT II meter to check any of the mains voltage at all.

Kyriakos is wrong that the highest industrial voltages are 380V 3Ø (phase to phase). While 380V 3Ø is a "common" voltage in the EU, it's not the only voltage used. In the US a common industrial 3Ø voltage is 480V and in both the US and EU electric motors are often 600V, 1200V and higher. It's also not true that you need thousands of volts to "arc over". US receptacles are designed to withstand 600V before arcing over (approx. 10mm gap). IIRC, EU plug gaps allow for a 1000V arc. They are designed this way to help shunt voltage in case of transformer failure or lightning strikes to ground. Transformer failures can cause huge voltage spikes lasting for many minutes at a time, and recurring when the automatic resets on the utility breakers keep trying to switch power back on. Mains power is truly a different beast and should be approached with extreme caution.

At the beginning of the 20th century, 1 out of 2 electricians were killed on the job. The numbers have come down drastically only because we are so much more aware of safe work practices and safer equipment designs.

[Kiriakos-GR]

While 380V 3Ø is a "common" voltage in the EU, it's not the only voltage used. In the US a common industrial 3Ø voltage is 480V and in both the US and EU electric motors are often 600V, 1200V and higher.

Ok ... ok ... but we talk here about multimeters , and the we do not teach the basics at the target group of industrial electricians of some factory , that it happens to own 2-3 electric motors that needs a 1000V to operate.

We have children's , fathers  and grandfathers , who just do basic measurements , in LOW power city network .. and  we should not scare those people , and look to them , as sellers of health  insurances,
that what usually do , are to repeatedly  remind you about 100 hazardous possibility's , in order to force you to buy, the damn health insurance contract ..    

Lets keep it simple .. lets not curred away , by creating a pile of  theory with out practical use .
If its hard even for one industrial electrician to find a motor with 1000V AC ,
why to bother all those people , with our debates about the absolute maximum limits ?

And , the point is that if I am measuring my own home plug , and at the same time  a massive lightning strikes the pole next to me and all that energy comes to my wall plug ,
I will survive , and be saved  because of the 400$  FLUKE ?

In such unpredictable conditions , its best to not be there at all .
 
If you are at the wrong place , at the wrong time, it called as accident , because it is one .

And there is no multimeter , that could handle such conditions, it just has not born yet,
and probably never will do .

  

[EEVblog]

Lets keep it simple .. lets not curred away , by creating a pile of  theory with out practical use .
If its hard even for one industrial electrician to find a motor with 1000V AC ,
why to bother all those people , with our debates about the absolute maximum limits ?

I thought I and others have been keeping it fairly simple.
The message is pretty clear, if you measure the mains you should get a properly designed name brand meter with a suitable CAT rating. At the very minimum a properly designed meter that doesn't have other dangers like poor quality probe insulation, exposed live metal screws or capacitor test sockets or whatever.
If you don't measure mains stuff then any old one-hung-low brand meter will do just fine.
So it really is a simple precautionary message.
IMO anyone who tries to argue the thin edge technicalities of it all is just being a twit.

Unfortunately some beginners and/or fans of el-cheapo meters don't seem to be able to comprehend or have respect for the potential dangers, so it unfortunately has to be explained to them ad nauseam, and the scary exploding multimeter videos help too!

And quite frankly almost any hobbyist will eventually want to measure the mains, so why not get that $50 name brand meter instead of the $10 one to begin with?

Dave.

[Kiriakos-GR]

At the very minimum a properly designed meter that doesn't have other dangers like poor quality probe insulation, exposed live metal screws or capacitor test sockets or whatever.

Dave.

a) exposed live metal screws ? .... its a damn plastic box , how it will become "live" ?  
b) test sockets ? ...  you will have  to spent allot of energy , and you will not win at the end ,
about making the planet to spin backwards  

But you are lucky ,  in the next 15 years , that all the TV sets will be 100% TFT - Plasma or what ever,
the small transistor slots , they will disappear from the face plate of multimeters .

Also because the new TV sets works with low DC , no one will care about CAT III other that some stupids electricians like me .  

But the capacitors slots , they will hunt you down for ever    as long there is even one electrolytic alive  ...

Take care Dave !!   ROFL  

I have meet and work with Australians , we was six months together.
We share the same passion as nations ,  when we stand behind of our opinions ..  
  

[XynxNet]

[...]
Hi Dave .... arc over = some thousands of volts .
We can search and find  at what specific voltage rate,
the electricity can arc over the distance of 11 mm of the classic small fuses, or the distance of 19mm,
of the large Fast acting ones .
[...]

When you massivly overload the classic unprotected small fuse, your fuse wire gets vaporized. The resulting hot metal vapor air mixture is mutch more conductive than normal air. Because of that the fuse can arc over at a much smaler voltage.

[Kiriakos-GR]

I took some quick lessons about fuses and arc-over, last night ..

Looks like , that the general rule are ... as much higher voltage fuse rating , the better about fuses build quality and behavior = anti arc over design .  

I have never bothered to look at high voltage fuses , because in everything that uses high voltage above 300V,  we secure the  220 input of the transformer by fuse , never the output.

The larger DC PSU that I have see from very close , was  selectable  700 - 2000V , and was used to power up the last tube ( stage )  ( RF amplifier )  (FM transmitter) of the American tubes ,
that they called as CX 4x250  or  CX 4x1000 , that produces large amount of RF power .

I had work - experiment - was my hobby -  the FM transmitters , but I was had always transistors as output ,like  dual  MRF317 , 250Watts on my antenna .
I had experiment and with tubes , like the EL-504 , but those was low output 25W ,
and the most that was able to handle , was as 300 - 400 DC at their anode.        

[alm]

c) We should not " force " the people , to throw away good tools , just from fear ,
that could " possibly "  blow - explode  ....  I recommencement to all who haves such instruments ,
to get an pair of " fusible probes " ... simple - effective - cheap.

Fused probes are a horrible idea in my opinion, the only reason why Fluke makes some is because it's mandated by some safety standard. Fused probes should only be used if you religiously use do a three-point test (known live circuit, circuit under test, known live circuit) for every measurement, otherwise they may incorrectly indicate 0V. I also doubt if a crappy meter plus fused probes offers the same safety as a real CAT II/III meter, will the fairly high-current fuse blow early enough to prevent any explosion or arcing?

But I do agree that applying industrial electrician standards to home use is silly, you'd be hard-pressed to find anything like CAT III 600V in most average homes, at most CAT III 380V (and for actual electronics usually CAT II/III 240V).

[TheWelly888]

Dave mentioned that no-one uses the transistor Hfe testers on the cheapo multi-meters. No wonder when they can only be used on low power outline ones such as BC558s etc and cannot be used at all with TO3 outline transistors such an 2N3055s!

I bought one of these for checking out discrete semiconductor devices ( BJTs, FETs and diodes ) and it's dead easy to use, just connect the leads any old where on the two/three legged thingy and it will tell you what the thingy is and what the lead outs are. http://www.peakelec.co.uk/acatalog/jz_dca55.html

[Waifian]

Or you could look up the data sheet if you need info on it.
Use the diode check function to see if its bad. You can also figure out if the BJT is a pnp or npn this way with out the transistor hfe "feature".

[Pradipta]

In my opinion, closed case (electronic) calibration is a thing to look out for. That leaves out the chance of a potentiometer being altered from a hard knock, among other advantages.
Basic input abuse the Dave way maybe a scale of choosing the odd ones out. Yes, people will say that it is callous to have a meter on ohms and hook up to the mains, but remember Murphy's law. Ironically, this is not rare anyhow. If one needs warning indicators and terminal blockers on the amps jack, the former can be highly probable.
Conclusion: best is the meter that you need. A student can not afford to use a 87 V and a mainstream professional can not afford to use a cheap chinese meter.

[EEVblog]

The cheap multimeter will be on their way soon, 5x $50 ones and 5x $100 ones. So we'll see what kind of meter you can get for not much money.

Dave.

[Kiriakos-GR]

The cheap multimeter will be on their way soon, 5x $50 ones and 5x $100 ones. So we'll see what kind of meter you can get for not much money.

Dave.

Alleluia  !!      

[EEVblog]

Conclusion: best is the meter that you need. A student can not afford to use a 87 V and a mainstream professional can not afford to use a cheap chinese meter.

Thankfully there are MANY good meters in between. It's certainly possible to get a good quality safe brand name meter for around the $50 mark. The upcoming Multimeter shootout will be interesting to see what they have to offer for the price.

Dave.

[desolatordan]

Are you also reviewing one of the cheap-o $3 dollar ones?

[EEVblog]

Are you also reviewing one of the cheap-o $3 dollar ones?

No, I think that would spoil it, and I don't think I could ever stoop so low as to seriously review a sub $10 meter.
The idea is to find the best value and well made meter in two different price categories. In this case it's around $50 and $100. The $100 mark ones all have TRMS.
I could of course have a $10 category as well, but of course that's kinda pointless because they are all equally shit IMO!

Dave.

[saturation]

Are you also reviewing one of the cheap-o $3 dollar ones?

No, I think that would spoil it, and I don't think I could ever stoop so low as to seriously review a sub $10 meter.
The idea is to find the best value and well made meter in two different price categories. In this case it's around $50 and $100. The $100 mark ones all have TRMS.
I could of course have a $10 category as well, but of course that's kinda pointless because they are all equally shit IMO!

Dave.

It might be a good thing to demonstrate because consumers are more numerous than hobbyists, and far more than engineers.

So, you'll be like a Consumer advocate/Report and you can show:

you can show what those marking mean, and if they have none
how accurately they track compared to better meters
how safe they are under CAT II, most home use, and III, home appliance use

Usually, such things will make the general press and even TV spots.  

As the late 'Steve Irwin' was to wildlife, you could be to electronics.  As you suggested in one video, there is a resurgence of the hobbyist, hacker, maker crowd, so the timing could be ripe for even a spot on the Discovery channel, like Mythbusters.  You never know, but seize the moment.

I can see it now, instead of 'crickey' it'll be 'its garbage!' 

There are a large number of hacks being done everyday, mostly quietly, and mostly in Asia, who are constant trying to get more from their devices.   A lot are in cellphones, a lot of are quasi-legal, and it differs from model to model, and brand to brand, so there are lots of opportunities for material.

[Kiriakos-GR]

Are you also reviewing one of the cheap-o $3 dollar ones?

After an such question , I can only imagine the face of Dave , getting smokes from his ears  

When just an cheapy crappy leads set, cost more than 8$ , and the proper ones for 15$ and more,
how in earth we should care for the for the 3$ DMM .

And I speak in positive spirit.
I am not trying to make fun of anyone, or be nasty.

The culture of this blog , has to do , at list from what I have understand so far,
with common problems and issues , that would possibly bother , the mid class of the knowledgeable technicians in electronics.

Even I , have seconds thoughts , like that it is possible  the Greek "Mid level" to not qualify with the international one, and that translates to , that I do not fit in here.  

In any way ,  Dave was clear enough , he will evaluate from the 50$ range and up, and nothing less.  
(even my own cheapy , pictured few pages back, got it at 1992 with cost as 95$ . )

Edit: looks that my reply came delayed , but I will let it live ..  

[PetrosA]

I agree with Dave and Kyriakos - you have to draw the line somewhere.

A student can drink a few less beers or smoke less to save for a slightly better meter
A professional in a country like Greece or Poland (I lived there for 14 years) can save some money to get the best they can afford
You can buy something used to save a few dollars
Hacking a cheap meter would be a waste of time


I seriously doubt that consumers are a large group buying multimeters. Unless you have unlimited funds, most of us who need them will be trying to save money on what we buy but the equally important lesson in all of this is not to sacrifice safety for savings. We can't afford that.

[Simon]

I think the blog was aimed as mentioned earlier in the topic at people buying their first meters, I think most of us would prefer and need to spend the price of one bench meter on a number of neccessary handheld multimeters before buying a bench one, I currently have 5 handheld meters which I trust to various degrees and have to make do with my new amprobe AM220 as my master meter, I'll be buying a decent fluke long before i can afford a bench meter