ESD Systems - Questions And Answers

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Our Combo tester does test within the Acceptance Limits of EIA-625, but not at the maximum or minimum values. The ESD Association is currently re-writing this document and will make it compliant to the ESD S20.20 standard which directly replaces the MIL-STD-1686 standard. We feel these values are not safe, either for the operator or the ESDS device. Lower limits: Underwriters Laboratory will list our foot grounders and wrist straps only if they have at least a 1 megohm resistor in series with the ground strap. This brings the lower range up from 250 kilohms (EIA-625) to about 1 megohm. The reason for this 1 megohm resistor is to limit the current to the body from an electrical hazard under 250 VAC. Upper Limits: At the other end, EIA-625 states the highest value to be 1 gigohm, one order of magnitude higher than we suggest. At this resistance, the discharge time is close to 1 second versus 92 milliseconds for a value at 100 megohms. When typical body movement is about 500 milliseconds, you can put at risk the ESD sensitive components you are trying to protect when your equivalent resistance to ground is at 1 gigohm, based on Table II in the above mentioned paper. Our Combo Tester’s calibrated limits are 750 kilohms +/- 10% to 10 megohms +/- 15% for the wrist strap test circuit and 750 kilohms +/- 10% to 100 megohms +/- 20% for the foot ground test circuit. If this is still an issue, we can factory adjust our testing values to exactly meet the current EIA-625 document with our new deluxe combo tester. What we need to know is if you employ lower resistance foot wear or mid-resistance footwear (250 kilohms or 500 kilohms). Our Deluxe Combo Tester can be set up to 1 gigohm. This was done primarily for the footwear (shoes) guys

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