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How should I test my ESD mats?

By rodion15
Jun 13, 2015
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  1. I have 4 ESD mats at the computer workshop I work. The ESD mats are interconnected and one of them is connected to ground through a resistive socket (or whatever it's called) which must be several Megaohms because my Ohmeter cannot read it (it reads up to 2MOhm). Yesterday I did this test: I used a voltmeter set to AC voltage, negative probe touching the ground in a socket, the other one between my fingers. I measured 2 volts. Then I put on the ESD wrist-band and I was surprised to find that not only did the voltage go down, it rose to 2.2volts!. It looks like this mat isn't working, am I right?
     
  2. jobeard

    jobeard TS Ambassador Posts: 9,342   +622

    Never heard of a 'resistive socket' but the concept sounds correct.
    The object is to absorb the energy to avoid the immediate discharge. However, we use capacitors for that and may be the reason for the ohm meter test results.

    I would expect a resistor->capacitor->earth.ground type of circuit. The capacitor absorbs the energy and slowly drains it back to the ground. The resistor slows the charging of the capacitor to avoid the immediate ESD.

    Your 2v DC test is not correct either. ESD is high voltage of a very short duration and the mat+socket would not respond to low voltable, long duration.
     
  3. rodion15

    rodion15 TS Booster Topic Starter Posts: 130

    Thanks for your answer: I said 2v AC not DC. I don't understand what you say, never heard a capacitor is used to discharge ESD, could you recommend some article or website explaining this?, not to advanced if possible. I mean, if I measure 2v AC (I think it was 2.2 volts) between my finger and ground, it looks like that can potentially damage an ESD sensitive component, doesn't it? I'm talking of laptop repair components.
     
  4. jobeard

    jobeard TS Ambassador Posts: 9,342   +622

    (1) ESD is high voltage of short duration
    (2) the Discharge is broadband of frequencies - - meaning Radio - - not just 50/60cps like our house current.

    Electrical R/C circuits (Resistors and Capacitors) are standard electronic components and it's basic electronics 101. Look it up.
    IMO, 2.2vac would never harm anything although I would expect that wearing a wrist strap should place your body at earth ground (ie 0.0vac) and the room wiring is suspect imo.

    We had a lab in the 80's where you could 'feel' a tingle touching an equipment frame. Upon inspection, the grounding for the floor was rusting and a new ground system created.

    ground should always be ground :)
     
  5. rodion15

    rodion15 TS Booster Topic Starter Posts: 130

    I see...So then, if you could answer to my question "How should I test my ESD mats?". Isn't my test good then, simply putting on your wrist band and checking that voltage to ground goes near 0? Should I use AC or DC in the voltmeter?

    By the way, with "resistive socket" I meant the earth bonding point ;)
     
  6. jobeard

    jobeard TS Ambassador Posts: 9,342   +622

    I've done a lot of tech lab stuff, but you need more than I can provide - - seek professional assistance.
     
  7. jobeard

    jobeard TS Ambassador Posts: 9,342   +622

    hmm; small wonder we don't understand each other.
     
  8. rodion15

    rodion15 TS Booster Topic Starter Posts: 130

    come on, there's no need to be sarcastic
     
  9. jobeard

    jobeard TS Ambassador Posts: 9,342   +622

    Sorry, but technology has precise terms with meanings. So does electronics. When you say something like "resistive xyz" you grossly mislead the reader when we get to hear later "I meant earth ground". That's not sarcasm, it's miscommunications. Having built shortwave mobile transceivers, worked on aerospace and oceanographic equipment - -

    Never mind.

    Again, I'll be kind - - seek professional assistance.
     
  10. rodion15

    rodion15 TS Booster Topic Starter Posts: 130

    Examine yourself: what did I ask? What did you answer? If you don't know how to adequately answer simply don't answer.
     
  11. jobeard

    jobeard TS Ambassador Posts: 9,342   +622

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