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Question I understand that the ESDA standard for checking footwear call for specification of RTG at 1 x 106 - 1 x 109. (ESDs9.1-1995) If the lowest range acceptable for footwear is 1 x 106 ohm , why is it most of the footchecker found in the market has a lowest range at 800 kohm @900 kohm and not 1 mohm ? (like the one sold by simco, dou yee, etc...) say for example a shoe has a RTG at 9 x 105. This will mean that it will pass the shoes checker which has the lowest range at 800kohm but will not pass the one which has the lowest range at 1 x 106. (like the one sold by Semtronics EN625) -June Tan, Selangor, Malaysia
Answer Actually, the ANSI/ESD-S20.20-1999 recommends that the resistance for footwear be less than 1x109 ohms and do not specify a lower range. In this case, footwear is referred to as shoes only and does not include foot grounders.

For foot grounders, the ANSI/ESD-S20.20-1999 recommends that the system resistance of the floor and the wearer be less than 35 megohms (35x106 ohms) and again does not specify a lower range.

In both cases the lower range is really dictated by the application and safety concerns. Regarding safety, UL will only list products that include a lower resistance boundary of 1 megohm using currently available technology. Current technology readily has available carbon film resistors with a tolerance of +/- 10%. This would mean the minimum resistance you could run into would be 900 kilohms (- 10% of 1 megohm). Add to this the tolerance of the measuring unit/system and you could have a range as wide as 15 to 20 %.

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