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Help finding an ESD tester circuit for real time monitoring on a bench — Parallax Forums

Help finding an ESD tester circuit for real time monitoring on a bench

WBA ConsultingWBA Consulting Posts: 2,935
edited 2011-02-02 05:49 in General Discussion
Once in a while I come across a something that has a high price tag without any justification. I believe I found one today: A real time ESD worksurface monitoring device. These little devices are used to monitor the grounding status of a workbench and an operator that has an ESD wrist strap plugged into it. Here's an example of a very basic one at Digikey for $261.

Anyone know what magic is going on inside that box? I had an old non-working one from a while back and there was a large glob of potting compound over some parts in the center of the board, so my guess is a micro-controller is involved. I would like to see about using a Propeller to make one if I could just figure out the circuit design.

Comments

  • Kevin CookKevin Cook Posts: 159
    edited 2011-02-01 09:22
    You could probably design an ESD testing circuit based on the information in the article:

    http://www.esdjournal.com/techpapr/eosesd/grounds/fsg.htm
  • davejamesdavejames Posts: 4,047
    edited 2011-02-01 09:26
    How does an ESD constant monitor work?
    Reliable performance of ESD matting and ESD wrist straps is critical for your product's integrity and reliability. Yet hand testing and hand logging wrist straps and table top material performance is a cumbersome, labor intensive paperwork nightmare. Use of our ESD wrist strap and ESD bench mat monitors continuously verifies the effectiveness of your ESD protected workstation, simultaneously satisfies ISO logging requirements and insures outstanding product quality.

    Operators plug their Transforming Technologies’ ESD coil cord into the grounding jack of the constant monitor right at their workstation. The constant monitor grounds the wrist strap and simultaneously monitors for faults in the ground path from the strap to the earth ground, including proper contact to the operators skin. A proper working ground path results in the LED on the constant monitor to glow green (indicating GOOD). If a fault is detected, the LED will blink red (indicating FAULT), and the unit will repeatedly beep.

    Types of monitors Transforming Technologies carries include:

    •Capacitance constant monitors- used with a single wire wrist strap.
    •Impedance constant monitors-uses a detection circuit designed to reduce false alarms and eliminate adjustments.
    •Resistance constant monitors- used with as two wire (dual) wrist strap.
    •Body voltage constant monitors- This type senses the voltage on a person’s body through a wrist strap.

    Found that information here: http://www.transforming-technologies.com/constant-monitors.html

    (I'm not affiliated with Transforming Technologies :smile:)

    I'm gonna guess there are some form of voltage comparators that look at the difference in potential between the ground plug, person, and work surface. Of course if the unit is not connected to a viable 'ground', efficiency is reduced. And boy do they squeal when an open path is detected!!!

    They actually work and they are an extra level of protection for those handling ICs at a bench.

    DJ
  • davejamesdavejames Posts: 4,047
    edited 2011-02-01 09:27
    Mr. Cook - good article, thanks!

    DJ
  • kf4ixmkf4ixm Posts: 529
    edited 2011-02-02 05:49
    here is a video article on element-14 i seen last week that uses an arduino as an emf detector. its a really simple circuit and i believe it could be used for esd...
    http://www.element-14.com/community/docs/DOC-26779/l/arduino-emf-detector
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