High energy discharges in digital multimeters

Discussion in 'General Electronics Chat' started by someonesdad, Jul 20, 2010.

  1. someonesdad

    Thread Starter Senior Member

    Jul 7, 2009
    Take a look at this video on applying some nasty overvoltages to some multimeters.

    On one hand, it's like putting a big magnifying glass into the hand of any red-blooded boy near an anthill on a sunny day -- you know exactly what's gonna happen.

    On the serious side, though, this is a good lesson for all users of DMMs, especially folks who operate in industrial environments. It shows why good protection being designed into the DMM is a good thing.

    Thus, when the experienced folks on this forum warn you about fuses, overvoltage protection, etc., it's worth paying attention to. It might even save you or someone you know from an injury some day.

    You'll find other interesting EE-related videos at http://www.eevblog.com/, so pay it a visit if you haven't been there before.
  2. sceadwian

    New Member

    Jun 1, 2009
    It's humorous and entertaining, but the only thing of value to learn from the video is never intentionally discharge a capacitor bank into a device rated for 1/4 or less of the the applied voltage...

    Following the basic safety manual prescriptions of a common DMM will preclude situations like this from every occurring in the real world, if they're followed, any real world situation where energies of this level are actually utilized, and anyone that doesn't know what they're doing that uses it gets what's coming to them.

    I work in an industrial environment, I've seen worse at common mains voltages. If there is even the glimmer of a chance of higher energy discharges all equipment should be safety rated from the highest voltage. In truly high voltage situations there is no way to truly protect aside from outright avoidance.
  3. tom66

    Senior Member

    May 9, 2009
    I would get a decent meter, if:
    1. I could afford one. I'm only a student with a limited budget.
    2. I needed one. I'm not measuring mains voltages; I'm sticking to less than 50 volts d.c. in most cases.

    My meter is not that accurate. It is only ±0.5%. Which is fine for me. But if I were doing precision applications, I would probably get a Fluke -or- a decent bench meter. What sold me on it was its fused 10A range (I already destroyed a meter with a dead short, and I have already managed to blow the fuse in the 500mA range), the cap test, the Hz mode, the audible continuity, and of course its price tag of £20.

    I have to say that my el cheapo meter does pretty well though for its price. I set it on ohms when measuring mains and it didn't blow up. It's fine on all the settings with 230V mains, capacitance and continuity. Hz measures the line frequency. I suppose I could have my meter exposed to a 4kV pulse, perhaps even higher, but I made sure to stand back when doing all these tests and I turned off the supply via. a proper isolation switch (not on the socket) until I had it set up...

    I opened it up. Pretty good construction. No input protection other than a wimpy PTC. So I'm not expecting too much from it. I'm certainly not expecting it to meet the 1000V CAT II rating it has.