EEVblog #94 – Near Death Multimeter ExperiencePosted on June 15th, 2010 62 comments
Dave was looking forward to reviewing the new Extech RC200 SMD Tweezer Multimeter, until the damn thing tried to kill him. Now he’s, well, kinda mad!…
The Cryrustek ES51928 DMM Chip: www.cyrustek.com.tw/spec/ES51928.pdf
My favorite (non-)review yet!
Maybe you should film when you’re messing with the devices, *just in case*.
Glad you’re not dead.
Glad to see you are ok, Dave.
were you able to do any different testing besides the voltage test in the socket?
… the main on the picture is a 20Amp rated 110V North American one, not a 220V one like in Europe or in Australia. You can even read it on the meter in the picture
(Still a really bad design, but I figured I’d point it out anyway)
eevblog.. the next cnet
for “anyone interested in electronic design!”
The link to the datasheet is bad, it links ‘http://www.eevblog.com/www.cyrustek.com.tw/spec/ES51928.pdf’
While it is nice and dramatic to stomp on the meter at the end of the video, it makes it harder for the manufacturer if they would like to see the actual meter.
Absolutely agree Dave.
Meters should be much more fool proof than this. Especially from a brand name manufacturer. Even trying to argue that you should have RTMF’ed first is unacceptable.
That is just ridiculous. What if you’re using it and it gradually comes loose until the switch disengages?
If your inspection is correct, I certainly wouldn’t feel comfortable using that to measure mains knowing that a small PCB mounted switch was all that was keeping the input protection in circuit!
What if the probe gets damaged in such a way that the switch doesn’t actuate?
Relying on a switch to engage input protection is a joke!
100% agree, it should be ‘safe’ by default, not the other way around!
RTFM for a multimeter? Perhaps if you never saw one before. 99% of all DMMs work virtually the same. Do I really need to read how to press mode and range switches to get the desired results nevermind meters with auto-range. Geez!
(Note that I’m Edd, not to be confused with the poster above, “Ed”)
Good video, Dave.
In your example schematic (or your theory of how the actual meter works), what is the point of the switch being set to dangerous mode? I mean, the probes measure everything that the tweezers do, right? So why not just remove the switch and have it always take the safe path to the microcontroller?
Is there something else, like improved accuracy that you get by having the switch go the unprotected route?
I am glad you have not been hurt, Dave.
Dave, don’t you think the protection circuitry that you showed from the data sheet would be sufficient to protect the chip from the mains voltage?
One branch is protected by a 100kOhm resistor which would limit the current to 2.4mA, a value the input diodes should be able to withstand.
The other branch is protected by a 15k PTC and zener diodes.
If mains voltage is applied, the PTC would quickly heat up and limit the current through the zener diodes.
Depending on the input voltage, this could die by overheating but should not explode.
If the charred resistor was the 100k from the data sheet, I can only imagine that it has failed because it was not specified for mains voltage.
If there was a sparkover at this resistor, I would expect such a severe destruction.
I am curious about the manufacturers analysis.
Damn thats one dangerous design for sure, no matter what you do to a meter it should never blow up on mains.(Well except switching to amps but the 10A range can usually handle that kind of abuse)
I wouldn’t trust any of these tiny meters for high voltages but come on its gotta work on mains.
What id really like to know is how the manufacturer responds as this is a serous danger
Does this meter really satisfy the EN61010-1 safety requirements? There is something wrong with the standard if this meter is not safe for the operator.
Extech datasheet have “EN61010-1 CAT III 600V” printed on the bottom right.
Glad you weren’t hurt, Dave.
Two things next time…gloves and CAMERA!!
Yeah, I know: One shouldn’t be expected to have to wear safety gear to do a standard test on a multimeter, but you see more than most folks go through the lab too.
The CNET crack was pure BS, BTW. Someone’s off their meds for sure.
I have one that seems identical, except for the brand (Voltcraft) and color (grey) : see http://www.conrad.fr/multimetre_cms_smd_200_p_53207_53652_855488
The PCB looks exactly the same.
When it works, it’s quite handy. But it often has problems :
- the auto scan doesn’t always recognize even a simple resistor or capacitor disconnected from any circuit.
- Sometimes when I switch it on, it starts beeping like crazy and won’t stop until I switch it off again (and even that isn’t always enough).
- Sometimes it goes in a loop switching between modes during auto scan without managing to select one, and disconnecting the component doesn’t stop the loop.
- Continuity test doesn’t always work and sometimes starts a loop like above.
Add to all this that after about half an hour of testing when I first got the thing, it simply stopped measuring anything. It turned out that the part where you plug the probes has two screws that are soldered on the PCB, and since you have to push/pull quite hard to connect/disconnect the probes (especially the voltage measurement ones, as you noticed) the solder had detached from one of the screws.
I have never tried to measure a voltage above 12V with this, and thanks to you I never will.
All in all, I consider this thing as a waste of money.
To be honest even with a rotary switch, quite often i’ve ended up hitting mains voltage with the meter on the ohms range or diode test or something by accident! I think it’s a pretty important feature for the device to be safe in all possible combinations of it’s use; mistakes do happen!
I’ve often taken my own safety for granted when using a multimeter and I think i’ve been lucky enough not to own any that are too dodgy!
Glad you weren”t hurt Dave.
Holy sh*t. Glad you were not killed, Dave. I work with mains voltage switching, and am super anal-retentive about safety and protection. RCD breakers. I have 2 (yup, 2) Tektronix P5205 differential probes for my Tek scope for measuring and monitoring floating voltages, and I ensure that the AC switching circuits under development are screwed tight into a proper test enclosure before powering up, etc…
Regarding Emmanuel L’s comments: if his meter is the same as yours but but different branding, I cam only conclude that this device is some crap made in China that Extech ordered from a factory but with their own branding. Reputation ruiner, if you ask me…
You didn’t read the manual?
HELLO!!! Think McFly, THINKKK!!!
Well you can’t call him chicken.
Glad you are not hurt. As you know at Fluke we voluntarily have our product independently tested to IEC61010. It would be great if this could be a mandatory requirement for all T&M product.
Why? If it was mandatory you couldn’t brag about how your stuff undergoes superior testing.
Maybe, but then you can brag about how you were first to subject your stuff to such a strict standard, before it was mandatory, even!
Strict standard? Yeah, that strict, superior independent testing didn’t catch 1,000s of dangerous Fluke clamp Meters last year (mine included).
Fluke has currently three recalls going on. http://us.fluke.com/Fluke/usen/Support/Safety/
But to be fair, some Asian manufacturers, if they would be honest and would care, should ship every single of their meters already with a recall notice.
I suggest a new safety mark for these. A clown’s face, superseding all the fake safety marks on their meters.
Interestingly I can’t find any of Fluke’s recalls on my country’s local Fluke website. I also couldn’t find any recall on the Fluke UK, Ireland or Spain websites. The Canadian website in turn has the recalls.
So much for “we place tremendous importance on your safety and the reputation of our products.” Who cares about a few dead Europeans?
I couldn’t help but laugh at the Google context ad for Extech appearing at the bottom of the video pane as you were proclaiming
“this thing is a piece of shit”
Love ya show, Dave but here’s the deal:
Whatever faults you find with that DMM, this was user error with a tool you weren’t familiar with, used on dangerous electricity!
WTF?! Hear me out, I bet this would have gone much more smoothly if you read the manual. This video was 80% adrenaline reaction and anger, and 20% good info.
Gonna go out on a limb and guess you don’t work on electrical stuff nearly as much as you do electronics. Electricians always check the swagger and bravado at the door.
Glad you’re okay but I echo Brian: Didn’t read the manual? Think, McFly, Think!
There’s a reason there are a lot of youtube videos of people doing stupid things around electricity.
The manual made no mention that there was a switch on “dangerous mode” by default, where you had to apply an unnatural amount of force to plug the probes in.
FLUKE have some explaining. LOL. They couldn’t keep themselves from getting in on the low-blow comments? Hah!
The funny thing is, FLUKE reacting is the best compliment they could’ve given to Extech, IMHO.
At 100 dollars is very easy for many of us that have an understanding of good meters and exactly what were measuring, to call the Extech a mediocre meter that deserved the death it received in the lab.
On the other hand, if my back round was not in Electronics, or if I was a beginning student trying to impress myself with a 100 dollar meter that exploded on the mains. I would be jumping up and down like Dave.
The meter should be more failsafe. It was destroyed to early in the blog to appear useful, and “sort of” gave me the impression of a cheap Chinese copy. Any meter that could fail during a product familiarization process should be looked at again. By the designers.
Assembly personnel and students that might experiment with line voltage would not accept the quality for the hard to get hundred dollars they paid. The Exteck needs to be more slightly more idiot proof and maintain its quality at the same time.
I would be pissed……
Measuring voltage on the ohms scale is bad karma all the time. I once did it on a “real” (it actually had a meter) multimeter (back in my youth, the late 1950′s). The result was that the needle of the meter was moving so fast as it hit the far stop of the meter it sheared off the needle at that point. Quite dramatic to say the least. Being smart (and shocked) I removed the leads from the power source quite quickly and resumed working. That meter actually suffered no damage OTHER than a shortened needle on the meter, and I used it for quite some time after that.
The problem on this meter is a MECHANICAL one where the silly switch wasn’t activated to put the device in “safe” mode without LOTS of pressure. That is the problem, and NO reading of the manual will overcome it. The default should be “safe”, and the tweezer probes should activate the “smart” mode. Common safety should prevail here. Think how interlocks are designed and go from there.
Excellent (and proper) review!!
You nailed it. The default should be safe. Either the applied safety standard is shit, not requiring this, or the safety standard compliance of the meter is an utter fake.
And then there is the issue how any engineer with working brain cells could come up with such a setup. That really smells like rebranded Chinese crap.
I agree, the safe mode should have been the default, so that if the probes were not pressed fully home then the instrument would still be safe to use (if not functional).
But even the other problem whereby the manual clearly states that high voltages should not be measured unless it’s in the correct mode, I would suggest that this is still a failing of the manufacturers of the instrument because a) you could accidentally press the range button while the measurement is being made and b) you could make an honest mistake and accidentally have it set to the wrong mode before you took the measurement. I don’t know how many times I’ve gone to take a voltage measurement and realised that I’m still set to resistance mode. It happens. Perhaps it makes me stupid, but it should not under any circumstances compromise my safety.
Good to hear that they’ve admitted a problem exists and that they’re working on it though. To be honest, I do have some patience and respect for a company who will publicly admit to an error and seek to correct it. It’s the ones that try to cover it up and refuse to admit to a problem that get a black mark in my book. Let’s hope they give Dave appropriate feedback and are transparent with their findings. We’ll see.
I think you were too easy on them. The backwards voltage measuring switch is only half the problem. Even when in
Leaving aside the fact that it did try to kill you, there is one comment really annoys me. “didn’t to read the manual”. I would personally always read at least the safety warnings – they are there for a reason.
Generally, I grant you most of the warnings are common sense (who has a ladder saying “don’t re-position the ladder when standing on it”) but sometimes there are things there you may not have immediately thought of. If you don’t realise that a radio transmitter might stop your pacemaker you would be glad of that waring in the manual.
Also, someone has spent (or should have spent) a long time on that manual – there hard work should be appreciated.
(Yes I do quite often end up writing (or correcting) the user guides for stuff I design)
Glad you didn’t get hurt. When measuring lethal voltages I always use something other than a toy gadget like that thing.
Why don’t they just have the protection of my cheap meter (~
Hi Dave, great stuff! so on the next multimeter review could you hook it up to 240V on the wrong range and see what happens?
I would be surprised if all of the multimeters in your last review could survive that test and I’d say it’s worthy of mention for those that do make the grade.
Anyway, just thought I’d mention fused test leads. I’ve been using fused multimeter leads for over a decade and now swear by them. Get the protection at the *business* *end* of things.
Then no matter about internal meter faults or damaged cable insulation or what the idiot user (i.e me) does it’s less likely to behave like a bomb. One thing you must remember to do a meter check before any test for live mains to guard against false indication if the fuse is blown – but hey you do that already, don’t you?
Having said that I’ve not blown a test lead fuse yet, ever. And the only time where I would have was when using unfused leads on a multimeter to check live mains – and after the bang I realised one lead was plugged in the 10A socket, oops!
Since that experience I like to keep a strip of insulation tape over the 10A socket, which is rarely used anyway.
My first reaction was “The meter wasn’t Engineer
However,your description of the design makes me
agree that it is a “piece of crap!”
One point I’d like to make is that holding the
meter while reading mains voltages is unwise.
I usually rest the meter on a table ,chair,the
floor,whatever,& plug the probes into the power
socket so I don’t have to hold them either.
The possible fault currents from the mains tend to
make me paranoid about the correct setting of the
It is wise not to rely on protective circuits,
which after all were designed by Engineers!
I’d like to see a reenactment of the 240V measurement
Another Extech produt to review would be the Light meter. It seems to be sensitive to static fields which requires you hold your body completely still and warn others not to walk near the meter when making mesurements. Any movement causes the readings to bounce around. (not due to light changes, The sensor was completely isolated)
I’ve watched this one through twice now, and am glad Extech confirmed the problem. A number of people have mentioned that it is not, at least in this incarnation, a failsafe design. It should fail, i.e. default, safe, and this doesn’t.
Apart from occasionally exceeding a voltage or current range (on manual range only meters), or possibly going over the maximum continuous current for more than 30 seconds – oddly, the manual for my last meter did not say what the maximum continuous current was – I have never abused any multimeter, but I would expect a digital one at least to be able to withstand contact with up to 265V AC, at least when using the ordinary probes, when connected between the volts and common jacks. I know the current ranges put a resistor, or for high current, a piece of very stout wire, across the jacks, and this is partly why current ranges should be fused. I have never owned a meter with an unfused current range. There is more risk to what is under test than to the meter, but that is not to say the meter can’t fail other than at the fuse.
In the first of R.A.Penfold’s books on using multimeters, he recalls a conversation he had with an electronics retailer, about a large number of analogue meters they were receiving returns on, all with overload damage. The problem was that the users did not read the specification fully, and some, on reading that the meter was protected to 250V AC, tried it across the mains in various ranges. However, the specification did state that this protection only applied to the voltage measurement ranges. All the overload damage was consistent with abuse of the resistance or current ranges. The warnings in the manual were beefed up. He cautions against deliberately abusing a multimeter. However, Dave’s testing is “real world” – I’ve known people try to measure voltage on a resistance range, or with the probes attached for current. In all cases, the “oops” reaction of these – often, at least – professionals, was bigger than any damage done to either the meter or the device being tested. Certainly, a digital meter connected for measuring volts should be safe on any mode.
Some manufacturers, such as Gossen, are fitting shutters to reduce the chance of a wrong connection occurring. A good idea but it seems only to be available on the most expensive meters. Anything that will fail safely, though, even if it leaves the meter needing repair, is good. Anything that fails otherwise is failing “wrong side” and ought not to be let out of the factory.
I believe a serious issue has been overlooked in the comments – the force required to fully seat the conventional probes into the meter.
Is there now a streangth requierment to use a DMM? Should a person of small stature or one with a disability be prohibited from working in electronics? What about a young person?
No DMM should require physical strength to use safely. I know it is difficult to maintain tolerences in molded plastics. Therefore, the DMM should be safe for the weakest user. As Dave (and others) have said, the DMM should DEFAULT to the safest mode.
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