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 Dual Operator Workstation Continuous Monitor
cannot be “fooled”. It will provide a reliable alarm only when
the wrist strap or work surface becomes dysfunctional or
unsafe according to accepted industry standards. The Dual
Operator Workstation 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 Dual Operator Workstation 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.
The dictionary defines constant as uniform and unchanging,
and continuous as uninterrupted. Nonetheless, 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 Association guidelines for
the 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.
Installation
Confirm that worksurface is 5 x 10
8
ohms or less.
Remove the monitor from its packaging and inspect for any
shipping damage. Included with each Dual Operator
Workstation Continuous Monitor should be:
1 120 VAC transformer
1 Work surface ground cord
1 Push and clinch snap (09863)
2 Remote Jacks (98201)
2 Mounting screws
The Model 19208 is normally installed under the bench top
toward the front edge of a workstation where the LEDs are
easily visible. The unit is designed to be mounted using the
mounting bracket provided. See figure 2. To release
monitor, push up on the monitor release tab.
Figure 2. Installation of mounting bracket.
Figure 3 shows the monitor as it is viewed from the front.
TB-2084
Page 2 of 4
Monitor
Release Tab
TO WRIST STRAP
TO WRIST STRAP
Figure 3. Operating the 19208 monitor.
REMOTE JACKS
The remote jacks allow you
to install the continuous
monitor up to 6 feet away
from the base unit. Two
persons can be monitored
at separate adjacent
workstations.
DESCO WEST
- 3651 Walnut Avenue, Chino, CA 91710 • (909) 627-8178 • Fax (909) 627-7449
DESCO EAST
- 90 Hudson Road, Canton, MA 02021-1407 • (781) 821-8370 • Fax (781) 575-0172 • Web Site: http://www.desco.com
*1981 article by Donald E. Frank - Electrical Overstress
Electronic Discharge Symposium Proceedings
