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March 2002

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Subject:
From:
Gene Felder <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 7 Mar 2002 13:38:25 -0600
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ANSI/ESD S20.20 covers items susceptible to damage by electrostatic
discharges greater than or equal to 100 volts Human Body Model (HBM).
Wireless wrist straps do not reliably remove charges to less than 500
volts.

Here's information from a company selling wireless wrist straps:
"In effect, the wireless wrist strap slowly neutralizes static electricity
on a human body and maintains the potential of a human body below 500V,
which is a great improvement from 3 to 5 kV measured without the wrist
strap.
The wireless wrist strap is not intended to replace conventional wrist
straps. However, a wireless wrist strap, supplied with an additional coil
cord for direct grounding, not only replaces conventional wrist straps, but
provides additional protection when a person using it has to move away from
the hard wired grounding point, (which is often a case in the electronics
assembly, kiting, stock room, inspection, service or development working
environments).

Source: http://www.bomir.com/online/zerocharge/ground/wireless.htm
Practical Points, Benefits and Precautions:
* Please, do not touch electronics components immediately after installing
the wireless wrist strap on your wrist. Allow minimum 60 seconds for the
wrist strap to neutralize high levels of static electricity already
existing on your body.
* Do not use wireless wrist straps as your primary grounding device (unless
it is a 2 in 1, Model AML-301A and is used with the grounding cord)."


Source: www.bomir.com/online/zerocharge/ground/wireless.htm


See http://www.esdjournal.com/techpapr/sfowler/wireless.htm
Evaluation of Wireless Wrist Straps
by: ESD Journal Lab
We have been asked many times over the past few years about the viability
of wireless wrist straps. The following is our evaluation of one wireless
wrist strap.
We used a wireless wrist strap that is advertises :
"It operates using a combination of several physics phenomena like "Ion
Neutralization,
Skin Effect, Point Discharge and Corona Discharge Effect" combined with the
principle of differential potential to collect and dissipate static
electricity.
It is a combination of bio-industrial and electronic technologies.
In effect, the wireless wrist strap neutralizes over 80% of the static
electricity on a human body and maintains the potential of a human body
below 150V which is low enough to protect electronic components."
The following is a summary of our evaluation of the strap:
The wrist strap came with a conventional cord for use at the workbench.
However, it is claimed to neutralize the static on a person without the
cord attached "after 15 seconds."
* Our tests showed that the wrist strap when connected by it cord had a
resistance from the wearer's hand to ground of 1.3 MegOhms.
* Our technician wore insulative shoes (> 10,000 MegOhms) and walked on an
insulative floor.

* We charged the technician to 2,000 volts.

* When and he walked around with the uncorded wrist strap on, we saw a
decay of the static charge to about 1,000 Volts in 90 seconds.

* When and he walked around without the wrist strap, we saw a decay of the
static charge to about 1,000 Volts in 90 seconds.

* There was no difference in the time to decay to 1,000 with or without the
wrist strap in place.

* With the wrist strap on the walking technician, his potential never went
below 700 volts for over 3 minutes.
We dissected the wrist strap to see what inside would account for the
claimed neutralization. We found only a 1 MegOhm resistor. This supports
our findings that the wireless wrist strap no method for neutralizing a
person not connected to ground by a conventional cord.
It is our opinion that no currently available methods or devices exist
which will effectively ground a person without a tethered cord to ground or
at least a large capacitance.
Sorry! Something that sounds too good to be true probably is.

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