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This ground snap therefore grounds the
entire garment and the operator. The monitor cuff on the wearer's
left and connected monitor snap allow constant resistance monitors to
measure the continuity of the garment, human operator and their connection
to ground.
Taken as a whole, the garment system's
electrical path is monitor-to-cordground-snap, conductive fabric, ground
cuff, operator's body, monitor cuff, isolated path, monitor snap,
cord-to-monitor.
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To
understand what the monitor is seeing, we have to look at the cord,
garment, and human operator in terms of their series resistance (see fig
3). There are five resistances to be considered.
Two of them (R1 & R5 in the figure) are 1 Megohm current limiting resistors in standard ground cords. The other three are the resistance of the garment, the resistance of the human operator, and the resistance of the monitor connection to the human operator (R2, R3 and R4 in the figure). In most applications and in most environments, this total loop resistance add up to about 6 Megohms. However, the reality is that this ideal situation rarely exists in most day to day situations for the long term.
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There
are a couple of innate factors that prevent this ideal situation.
For instance, infrequent and/or improper laundering of the
garment may increase the resistance in the cuffs and/or in the garment
itself. Also, the
resistance in the human body varies widely from person to person, the
value being dependent on many factors, but most importantly on the
condition of their skin. While most peoples resistance measures in the area of 2X104 20,000 ohms) to 5X105 (500,000 ohms), there are individiuals who,
because of their dry skin, measure as high as one or two Megohms.
If you add a 2 Megohm person to our loop in the place of R3 in
the figure, our total loop resistance goes up to about 9 Megohms,
dangerously close to the "fail" point of a 10 Megohm monitor.
Tech Wear
Inc.’s X2 dual-path garments are available in a variety of styles,
fabrics and colors. These
patented garments come with a 100 wash guarantee.
That means that the garments will meet the National
ESD Association STM 2.1-1997 for static control garments through 100
washes and will remain compatible with your dual monitor set at 35
Megohms.
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