Desco 19208, 19209 Technical Bulletin

independently monitors the operator and the work surface.
The instant an operator’s wrist strap or cord fails, the
monitor will issue audible and visual alarms alerting the
user of the problem. In the same manner, the unit also
confirms that an electrical discharge path to ground of less
than 500 megohms exists from the ESD protective work
surface. No user adjustment or calibration required.

ADVANTAGES OF CONTINUOUS MONITORING
OVER PERIODIC TESTING

Many customers are eliminating periodic testing and are
utilizing continuous monitoring to better ensure that their
products were manufactured in an ESD protected
environment. Full time continuous monitoring is superior to
periodic or pulsed testing, and can save a significant
amount of money in testing costs and rejected product.
Periodic testing detects failures after ESD susceptible
products have been manufactured. The costs of dealing
with the resulting catastrophic or latent defects can be
considerable. Dual Operator Workstation Continuous
Monitors eliminate the need for users to test wrist straps
and log the results; by their function, these monitors satisfy
the ISO 9000 and ANSI/ESD S20.20 test logging.
ANSI/ESD S20.20 Paragraph 6.2.2.2 Personnel Grounding
Guidance states “A log should be maintained which verifies
that personnel have tested their personal grounding
devices.” Per ESD-S1.1 Paragraph 6.1.3 “Daily (wrist strap
system) testing may be omitted if constant monitoring is
used.”

WAVE DISTORTION DETECTION TECHNOLOGY
PROVIDES TRUE 100% CONTINUOUS MONITORING

From all the technical alternatives available, Desco
Charleswater has chosen wave distortion technology for all
its Continuous Monitor product offerings. Wave distortion
circuitry monitors current/voltage phase shifts and provides
true 100% continuous monitoring. Electrical current will
lead voltage at various points due to the combinations of
resistance and capacitive reactance. By monitoring these
“distortions” or phase shifts, the wave distortion Workstation
Continuous Monitor will reliably determine if the circuit is
complete.

Wave distortion technology can be referred to as “vector
impedance monitoring”. This description is valid as the
wave distortion technology measures the impedance at the
monitored banana jack and looks for changes in either the
capacitance or resistance of the circuit which includes the
wrist strap and its wearer. It uses filtering and time domain
sampling to filter out false signals caused by voltage offsets,
60 Hz fields and other electro-magnetic and electrostatic
interference.

TB-2084 12/01 Page 1 of 4

Dual Operator Workstation Continuous Monitor
Operation, Installation and Maintenance

Figure 1. Desco Dual Operator Workstation Continuous
Monitor.

Description

Leading companies use continuous monitors as a cost
effective component in satisfying the paragraph 6.1.3
Compliance Verification Plan requirements of ANSI/ESD
S20.20. The Desco Dual Operator Workstation Continuous
Monitor continuously monitors the grounding integrity of two
operators, and an ESD protective work surface’s discharge
path to ground. The monitor will provide instantaneous
notification of static control equipment failures, eliminating
the need of costly record keeping. This unit is highly cost
effective as it is designed to monitor any conventional single
conductor wrist strap and ground cord system.

The Dual Operator Workstation Continuous Monitor is
available in two models.

The Dual Operator Workstation Continuous Monitor is an
impedance sensing device designed to monitor body types
from a 5th percentile female to a 95th percentile male. This
range covers a 5 foot tall 90 pound person to a 6 foot 5 inch
250 pound person in any production environment.* The
19208 is powered by a 120 VAC, 60/50 Hz, plug-in
transformer.

No user adjustment required: The Continuous Monitor is
drift-free and designed to be insensitive to the effects of
squeezing or stretching the coil cord. It requires no user
adjustment or calibration.

The Dual Operator Workstation Continuous Monitor is a
Real Time instrument that ensures that critical ESD
generators in a sensitive area are effectively grounded. It

*NASA Publication 1024-Anthropomorphic Source
Book Volume 1: “Anthropometry for Designers”

Model Voltage AC
19208 120 Volt
19209 220 Volt

DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]

DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

TECHNICAL BULLETIN TB-2084

Made in America

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 SINGLE­WIRE 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 dual­wire 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 108ohms 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 • [phone] • Fax [phone]

DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

*1981 article by Donald E. Frank - Electrical Overstress
Electronic Discharge Symposium Proceedings

Figure 4 shows the monitor as it is viewed from the rear,
with the work surface wiring in place.

Figure 4. Wiring connection instructions for the 19208.

The following procedure will outline how to correctly wire
the 19208 so as to properly monitor an ESD protected
workstation.

1. Use rear access connections when using monitor with
remote jacks. Access holes are provided on the bottom of
the unit to loosen/tighten connections. See Figure 4 for
wiring connection instructions.

2. Verify that a ground cord is properly connected to snap
socket on one corner of the ESD work surface. The other
end of the ground cord must be attached to a known good
ground point. After remote jacks are mounted, route wires
using a direct route; try to avoid running wires adjacent to
metal, if possible.

3. Confirm that worksurface surface resistance is 5 x
108ohms or less. Connect the stripped end of the work
surface cord included with the unit to the terminal marked
“Work Surface” on the back of the unit. Snap the other end
to the worksurface as shown in figures 4 and 5.

Figure 5. Installing cords on the worksurface.

4. A convenient 120 VAC outlet should be located and
tested for proper wiring and grounding. We recommend
Desco Item 98130 AC Outlet Analyzer to verify integrity of
building ground.

5. Plug the transformer into the outlet and connect the mini
plug into the back side of the monitor. The green Work
Surface LED should be lit. The monitor is now ready for
use. If the red Work Surface LED is flashing, check the
snap fasteners and ground cords for proper connection.

Installation on Micastat®Laminate

Materials Needed:
2 14244 Flush Mount Ground Laminate Inserts
1 14242 Installation Tool for Flush Mount Insert

1. Install the Flush Mount Inserts first. It is recommended to
install one in the right back corner and the other in the
left back corner of the Micastat®laminated bench top.

2. Once both inserts are installed, cut the ground cord
supplied with the monitor into two pieces; make sure that
the tinned end is long enough to connect from the
monitor to one of the flush mount terminals located under
the bench.

3. The remaining wire can then be used to connect the
other flush mount terminal to ground using the supplied
ring terminal. The shrouded molded end can then be cut
off.

When complete, one flush mount terminal will connect the
Micastat®laminate to ground, while the other will connect it
to a monitor. The monitor then monitors the ground
connection between the two inserts, and since Micastat® is
the only ESD laminate made with a physical uniform ground
layer, it will monitor the entire Micastat® surface ground.
The wires will stay under the bench, maximizing the usable
space on the bench top.

Operation

When the 19208 monitor is installed and is connected to a
grounded ESD protective work surface, the monitor’s green
Work Surface LED and its two red Operator LEDs should
be on.

TO USE THE MONITOR:

1. Plug a wrist strap cord, not attached to the wristband,

into either of the monitored jacks on the front of the unit.
This automatically activates the selected operator channel.
The red Operator LED should turn on and the audio alarm
should beep.

2. Snap the cord to the wristband, and slip it on your wrist.

(It should fit snugly.) This should silence the audio and
cause the LEDs to switch from red to green. If this does not
happen, check the coil cord for continuity or damage.
Examine your wrist and ensure that it has a secure fit. If you
have dry skin use antistatic hand lotion such as Desco Item
81080 Reztore™ ESD Hand Lotion.

When leaving the area, a person can take the coil cord
along or leave it attached to the monitor. In either case, the
audio alarm will only sound for about eight seconds.

TB-2084 Page 3 of 4

TO MONITOR

TO MOUNTING SURFACE

BACK VIEW OF

MONITOR

DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]

DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

TB-2084 Page 4 of 4

© 2001 DESCO INDUSTRIES INC.

Employee Owned

Whenever the coil cord is accidentally withdrawn from the
monitor, or if continuity from the user to the monitor is not
maintained, the alarm sounds, the green Operator LED
turns off and the red Operator LED turns on.

COMPUTER INTERFACE

The model 19208 monitor also incorporates logic output
circuitry. The unit is designed with an open collector circuit
that can be set up to activate remote sirens, alarms or
interface with a computer. The open collector circuit is
accessible through the terminal screw on back of the
monitor. See figure 4 for location.

WORK SURFACE CHANNEL

The 19208’s Work Surface monitoring circuitry is sufficiently
sensitive to detect extremely low current, allowing it to be

used with mats having a resistance of up to 5 x 10

8

ohms.

When the monitor is connected to a static dissipative
work surface, the amount of current that flows is a function
of the total resistance between the monitor and through the
work surface to ground. When the resistance of the work
surface is below a present threshold, the monitor will
indicate good. Conversely, if the resistance level is high
when compared to the monitor’s reference, the unit will
alarm. This is an integrating resistance measuring circuit,
therefore it is relatively insensitive to externally induced
electromagnetic fields. The resistance threshold is factory
set to 500 megohms. Custom worksurface range available
upon request. Call for details.

Specifications

Work Surface Limit* Set to 500 Megohms
Operating Voltage 120 VAC, 50-60 Hz
Response time to alarm < 50 mS
Operating Temperature 0 - 40°C
Long Term Drift <0.5% per Decade

(1st Decade is 1 hr)

Size (less bracket) 3.25 x 4.75 x 1.1

OPEN COLLECTOR OUTPUT
Fail-Safe: For fail safe operation, an active low is required.

If the monitor detects an operator-grounding fault, the open
collector port goes low (with respect to the green wire
ground).

One-Wire: Since the monitor detects that there is a low
resistance between the green wire ground and the neutral
conductor in the branch circuit, less than 1K ohms, the
green wire ground serves as the reference or the second
wire between the monitor and its remote warning device.
The open collector port is the other.

DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]

DESCO EAST - 90 Hudson Road, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

*Limits can be varied and set to 1 gigohm maximum.

Limited Warranty

Desco expressly warrants that for a period of five (5) years from the
date of purchase Desco Continuous Monitors will be free of defects in
material (parts) and workmanship (labor). Within the warranty period,
a credit for purchase of replacement Desco Continuous Monitors, or,
at Desco's option, the Continuous Monitor will be repaired or replaced
free of charge. If product credit is issued, the amount will be
calculated by multiplying the unused portion of the expected five year
life times the original unit purchase price. Call our Customer Service
Department at 909-627-8178 (Chino, CA) or 781-821-8370 (Canton,
MA) for a Return Material Authorization (RMA) and proper shipping
instructions and address. Please include a copy of your original
packing slip, invoice, or other proof of date of purchase. Any unit
under warranty should be shipped prepaid to the Desco factory.
Warranty replacements will take approximately two weeks.

If your unit is out of warranty, call our Customer Service Department
at 909-627-8178 (Chino, CA) or 781-821-8370 (Canton, MA) for a
Return Material Authorization (RMA) and proper shipping instructions
and address. Desco will quote repair charges necessary to bring your
unit up to factory standards.

Warranty Exclusions

THE FOREGOING EXPRESS WARRANTY IS MADE IN LIEU OF
ALL OTHER PRODUCT WARRANTIES, EXPRESSED AND
IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE WHICH ARE SPECIFICALLY
DISCLAIMED. The express warranty will not apply to defects or
damage due to accidents, neglect, misuse, alterations, operator error,
or failure to properly maintain, clean or repair products.

Limit of Liability

In no event will Desco or any seller be responsible or liable for any
injury, loss or damage, direct or consequential, arising out of the use
of or the inability to use the product. Before using, users shall
determine the suitability of the product for their intended use, and
users assume all risk and liability whatsoever in connection therewith.

Specifications:

V (open circuit) <20 V
I (short circuit) 200 uA
Pull-up to 15V >50 uA (Active)
Pull-up to 5V >150 uA (Active)
Pull-down to 0.5V >400 uA (Active)
Third-state HiZ >100 K ohms (unit unplugged)

Maintenance and Calibration

The Dual Operator Workstation Continuous Monitor is solid
state and designed to be maintenance free. The 19208 and
19209 are calibrated to NIST traceable standards. There
are no user adjustments that can be made. Because of the
impedance sensing nature of the test circuit, special
equipment is required for calibration. We recommend that
calibration be performed annually, using the #98220
Continuous Monitor Calibration Unit. Prior to calibration,

disconnect Remote Jacks (if used) from the unit.
Remote Jacks may cause intermittencies in calibration.

The Calibration Unit is a most important product which
allows the customer to perform NIST traceable calibration
on continuous monitors. The #98220 is designed to be
used on the shop floor at the workstation, virtually
eliminating downtime, verifying that the continuous monitor
is operating within tolerances.