In normal factory environments, and with persons whose
capacitance with respect to ground is within design limits
(5 feet tall 90 pound person to 6 foot 5 inch 250 pound
person), the Multi-Mount Continuous Monitor cannot be
“fooled”. It will provide a reliable alarm only when the
wrist strap becomes dysfunctional or unsafe according to
accepted industry standards. The Multi-Mount Continuous
Monitor is drift-free and designed to be insensitive to the
effects of squeezing or stretching the coil cord.
ADVANTAGES OF WAVE DISTORTION AND
SINGLE-WIRE TECHNOLOGY
The Desco Multi-Mount Continuous Monitor allows the use
of any standard, single-wire wrist strap and coil cord. The
monitor/wrist strap/cord system life-cycle costs are by far
lower than alternative systems which require expensive &
fragile dual-wire cords and special wrist straps. Dual-wire
cords are expensive and are the weak link of the system,
the most likely component to need replacement. Over a
five year period, this can make the dual-wire system three
to five times as expensive as a system utilizing single-wire
wrist straps and cords. See Maintenance and Calibration
(page 4) to minimize life-cycle costs.
The dictionary defines constant as uniform and unchanging,
and continuous as uninterrupted. None theless, some
dual-wire resistance monitors utilize a pulsed test current
and do not really provide continuous monitoring. For
example, during each 2.2 second pulse cycle of a leading
“constant” resistive monitor, electrical current is pulsed for
only 0.2 seconds followed by an unmonitored interval of
2 seconds. This leaves the user/wrist strap unmonitored
for over 90% of each cycle. Damaging static charges can
easily occur in the portion of the time in between the pulses.
The off period of 2 seconds equals 2 billion nanoseconds,
and “it takes only about 25 volts applied for 100
nanoseconds to blow most memories or microprocessors”.*
The dual-wire system does not reliably meet all industry
specifications, as the cords do not meet the EOS/ESD
S-1.0 paragraph 4.1.6, 1 to 5 pound “breakaway force”
requirement for operator safety.
By using the reliable wave distortion technology to
determine if the circuit is complete, there are no false
alarms. There is no need to adjust or tune the monitor to
a specific user or installation. The miniscule amount of
electrical current (less than 1 volt coil cord signal) required
to generate the waveform has never caused reported skin
irritation and is extremely safe for use in voltage sensitive
applications such as disk drive manufacturing.
Figure 2. Multi-Mount Continuous Monitor features and
components
Features and Components
(See Figure 2)
A. Status LEDs:
When the green LED is lit, the operator is
properly grounded. When the red LED is lit, the operator is
not properly grounded.
B. Monitored Operator Jack:
Where the operator inserts
the wrist cord banana plug.
C. Worksurface Ground LEDs:
When the green LED is
lit, the work surface mat is properly ground. When the red
LED is lit, the work surface mat is not properly grounded.
D. Operator Ground LEDs:
When the green LED is lit, the
operator is properly grounded. When the red LED is lit, the
operator is not properly grounded.
E. 4mm Parking Snap:
When touched by the operator, this
snap will deactivate the alarm for six seconds. This allows
time for the operator to disconnect the coil cord from the
wrist band and park it on this snap. While parked, the coil
cord disables the alarm, allowing the operator to leave the
workstation. The OPERATOR GROUND LED will remain
off while the cord is parked. Upon returning and removing
the coil cord from the parking snap, the operator has six
seconds to hook up to the wrist band before the alarm
sounds.
F. 24 VAC Power Jack:
Connect the power adapter here.
G. Mat Connection:
Monitors worksurface mat. NOTE: To
disable worksurface monitoring, shunt this terminal to the
neighboring GND terminal with a bus wire.
H. Mat Ground:
Grounds worksurface mat.
Installation
Remove the monitor from its packaging and inspect for
any shipping damage. Confirm that the work surface is 1
x 10E7 ohms or less and has a conductive layer such as
Dual Layer Rubber, Dissipative 3-Layer Vinyl, or Micastat®
Dissipative Laminate with conductive buried layers.
TB-3028
Page 2 of 4
*1981 article by Donald E. Frank - Electrical Overstress /
Electronic Discharge Symposium Proceedings
© 2011 DESCO INDUSTRIES INC.
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