Electroboom damages a cheap DMM - Page 1
Forum section: electronics / testgear

author: joeqsmith
author_rank: Super Contributor
timestamp: August 01, 2019, 11:59:13 am
content: I don't watch many of his videos but the EMP seemed interesting to me so I had a look. At one point, he uses a handheld for a non-contact demonstration and takes out the meter.Is this the beginning of a new era of non-contact meter testing?https://youtu.be/Y5M6YKR7wUw?t=602

author: Daruosha
author_rank: Regular Contributor
timestamp: August 01, 2019, 04:30:21 pm
content: I thought exactly the same immediately when I saw the the pathetic failure in the his video.

author: maginnovision
author_rank: Super Contributor
timestamp: August 01, 2019, 08:31:12 pm
content: I'm somewhat surprised he showed that considering how often he seems to recommend them. I may just seem to watch the videos where he talks about it though.

author: David Hess
author_rank: Super Contributor
timestamp: August 01, 2019, 09:44:14 pm
content: I have seen that sort of thing happen before with poorly designed test equipment.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 02, 2019, 01:18:07 am
content: It's a Pro'skit, so poor design is expected.I don't know how strong was the electric field, around the spark terminals, but there are a few reputable brand meters that would fail in a similar fashion.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 02, 2019, 10:48:22 am
content: You just need to try and find that same high voltage supply and attempt to use the same length of wire and set the gap the same. Then give it a try on some of your low end meters. I would try and repeat it, but I'm afraid that all of my low end meters were damaged beyond repair and recycled.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 02, 2019, 11:44:59 am
content: Quote from: rsjsouza on August 02, 2019, 01:18:07 amHigh voltage sparks are not to be underestimated!What he was applying, would easily induce several kV and many amperes in traces -- in interior traces and nodes, not just on external connections!Most devices are tested for ESD hits on external connections, and induced ESD from a nearby coupling plane and from stray charge on insulating surfaces. The former is relatively easy to protect against (filter and protect the signal lines in question), and the latter is usually weak enough not to be a problem (distance, and the partial shielding of a ground plane PCB, help greatly here).But with that loop, and the 10-20kV supply, and the high sparking current, and the relatively high repeat rate -- most commercial products aren't prepared for something so intense!The current -- ESD is usually tested with some series resistance, say 330 ohms, or 1.5kohms. This limits the peak current to, say, 10A or so. The capacitance is fairly small, and the pulse width fairly short (10s of ns).But this discharge has very little ESD -- it probably rings quite a bit, give or take how much the diodes can take.Those HV modules are an inverter feeding a CW multiplier; the discharge proceeds as a stack of capacitors into the lead inductance and arc voltage drop, a resonant circuit. That works until the voltage reverses and the diode stack turns on. Which, since we're talking 10s or 100s of ns here, forward recovery time may be of significance, allowing some reversal, but probably not much follow-through, effectively damping it after a quarter wave or so. The voltage waveform then, would be brief, but the current waveform will have a fast rise and a very long tail, as the inductance discharges into the diodes rather than ringing out.Those poor diodes, they might have to surge over a hundred amperes in that service... I wonder how long they survive into a sparking load.Anyway, the capacitors I would guess are larger (though, the total series equivalent may well be just a few 100 pF anyway?), and with little ESR, they can discharge quite quickly and with quite high peak current.So in short, it's not so much that the kit is poor quality -- it likely passed all the tests it was supposed to, and this definitely was not one of them! I wouldn't expect a lot of things (in plastic enclosures, at least) to survive this kind of test. It's a powerful transient!Tim

author: rsjsouza
author_rank: Super Contributor
timestamp: August 02, 2019, 06:06:15 pm
content: Quote from: T3sl4co1l on August 02, 2019, 11:44:59 amI didn't watch the video, but the figures you posted and the ensuing damage certainly make sense.This is radically different than a typical EN61010 test. Our product was zapped at very close range on its plastic housing an on metallic exposed parts by 2, 4 and 8kV sparks 25 times spaced within 1 second of each in both polarities and the unit still works fine. It is a regular USB-powered product without shielding at all. A zap gun is not continuous, thus energy was low.Electromagnetic field alone would need much more strength to damage something. My EM voltmeter can easily measure 20kV at 1cm way from a simple rubber balloon with static electricity. That field does not cause any trouble with my meters.