3M 724 User Manual
3
Model 724 Work Station Monitor
Instructions
2
Index
Section Page
Safety Information..................................................................................................3
1. Theory of Operation......................................................................................4
2. Installation of 3M™ Model 724 Monitor
with Work Surface Ground Monitoring.........................................................8
3. Installation of Model 724 Monitor
without Work Surface Ground Monitoring ...................................................9
4. Selection of Test Voltage and Resistance Limit ..........................................12
5. Mounting the 724 Monitor and 3M™ Model 732 Remote.........................12
6. Wrist Strap Connection...............................................................................13
7. Fault Conditions..........................................................................................14
8. 3M™ Model 3057 Standby Jack.................................................................15
9. 3M™ Model 733 Dual Conductor Remote Input Jack ...............................15
10. Installation of Model 733 Remote...............................................................15
11. Verification Procedure for the Model 724 Monitor.....................................16
12. Specifications ..............................................................................................19
13. Parts Included..............................................................................................19
14. Required Accessories and Optional Available Parts....................................20
15. Additional Wrist Strap Monitoring Information.........................................20
16. Warranty ......................................................................................................21
3
Safety Information
Intended Use
The 3M™Model 724 Work Station Monitor
is designed to monitor the operation of two
wrist strap grounding systems and two
work surfaces. This product has been
designed and tested for use with 3M
™
Dual
Conductor Wrist Straps and 3M Work
Surfaces Grounding Systems. For North
America this unit is designed for use with
an AC adapter included. Outside North
America, obtain an appropriate AC adapter
meeting the specifications as stated in the
user instruction manual (Section 12). Use
of other components may cause improper
performances and/or unsafe conditions. For
use outside of North America, grounding of
the Model 724 Monitor is recommended
through a separate ground wire with ring
terminal supplied (Sections 2 and 3).
CAUTION
• Incorrect grounding of an operator may cause electrostatic discharge (ESD) damage to
components or assemblies being handled. For proper grounding of the operator when
using the 3M 724 Work Station Monitor, use of the three-prong AC adapter specified
in the user instruction manual or supplied ground wire with ring terminal is required.
• Verify that the electrical ground point is suitable. If you are not sure what a suitable
ground is, contact a licensed electrician before installation.
Explanation of Symbols
– Caution: refer to user instruction manual.
– Operator(s) Wrist Strap Assembly Ground.
– W ork Surface Ground.
– Electrical ground.
– Power input connector polarity (center negative).
– See user instruction manual for explanation of the indicator lamps.
Read and understand all safety information before
operating this equipment.
4
Section 1.
Theory of Operation
The 3M Model 724 Work Station
Monitor (Fig. 1) is designed to
monitor the operation of the wrist
strap grounding systems of two
operators. To accomplish this, it uses a
DC current source to measure a loop
electrical resistance. The system uses
a special wrist band and ground cord
that contain two independent
elements.* The 724 monitor employs
two selectable test voltages (9 and 16
volts) and resistance limits
(10 Megohms and 35 Megohms).**
It also monitors the grounding of up to
two 3M work surfaces.
The Model 724 monitor performs a
resistance measurement by applying
an electrical current of less than 3 µA
approximately every 2.0 seconds for
0.2 of a second in duration. The path
for the current is through one
conductor of the ground cord that
contains a current-limiting resistor,
through one side of the wrist band,
through the skin of the wearer under
the band, through the second side of
the wrist band, through the second
conductor of the ground cord that
contains a current-limiting resistor,
and finally back to the monitor.
Selection of Test Voltage and
Resistance Limit
Fig. 2 - Resistance/Voltage switch selection.
Fig. 1 - Model 724 Work Station with dual conductor wrist strap assemblies and remote input jacks.
Model 724
Work Station
Monitor
Model 732
Remote
Input Jack
Model 733
Remote
Splitter Kit
Dual Conductor
Metal Wrist Strap*
Dual Conductor
Fabric Wrist Strap*
*Resistance values are ±15%
5
The Model 724 monitor allows for the
selection of test voltages (9v or 16v)
and resistance limits (10 Megohms or
35 Megohms). The additional ranges
have been added to accommodate
global Electrical Static Discharge
requirements. Selection of the
operating parameters are left up to the
user’s discretion (See Section 4).
Operator Monitoring Single and Dual
Fig. 3 - Face of Model 724
The wrist strap monitoring function
is activated by plugging a wrist strap
dual conductor ground cord into either
one of the jacks on the 3M™Models
732/733 Dual Conductor Remote
Input Jack. If the resistance of the
wrist strap loop is within the limits of
the selected range (1.5 Megohms to
10 Megohms or 1.5 Megohms to 35
Megohms)* on the Model 724
Monitor, the cord, the wrist band, and
the contact to the arm of the wearer, it
is considered to be functioning
correctly. At this time, one of the
(OK) green lamps (1 or 2) will be
illuminated on the front of
the monitor.
If the resistance of the wrist strap
loop is higher than the selected range
(10 Megohms or 35 Megohms)* on the
724 monitor, an (OK) wrist strap green
lamp (1 or 2) extinguishes, and
a high wrist strap red lamp (H)
illuminates with an audible alarm. This
is an indication of a high resistance in
the cord band, or poor contact between
arm and band. If the resistance in the
loop is under 1.5 Megohms,* it is an
indication of a low resistance meaning
one or both current-limiting resistors
are bypassed. The low yellow lamp (L)
will flash and an (OK) green lamp
(1 or 2) will remain illuminated.
Caution
A low resistance condition can also
be caused by touching a grounded
object or by standing on a
conductive surface.
The wrist strap of a second operator
is measured in the same way. Operators
are identified by the two (OK) green
lamps (1 & 2). However, the same high
wrist strap red lamp (H) and low
yellow (L) lamps illuminate when a
fault is detected. The green lamp that
extinguishes identifies the operator that
is experiencing the fault condition.
* Resistance values are ±15%
3M 733 Remote Splitter Kit purchased separately.
OK #1
Operator
OK #2
Operator
Resistance High Operator
Resistance Low Operator
Resistance High
Work Surface
6
Voltage on Operator
When Connected to the
Model 724 Monitor
There is a concern about the voltage
that is applied to an operator while
they are connected to a monitor. Some
of today’s electronic components are
extremely sensitive to electrostatic
discharge from a person (less than
10 volts). The following chart for
the Model 724 monitor illustrates the
level of voltage that will appear on the
operator under various resistance
conditions.
Note:
For more information about wrist strap
monitoring see Additional Wrist Strap
Monitoring Information (Section 15).
Voltage on Operator when connected to the Model 724 monitor
Condition 9V-10 Megohms 9V-35 Megohms 16V-10 Megohms 16V-35 Megohms
No Skin Resistance 0.9V 0.9V 1.6V 1.6V
200K Ohm Skin
Resistance 1.0V 1.0V 1.8V 1.8V
Likely Case Before
Alarm 2.5V 3.6V 4.4V 6.4V
Worst Case Before
Alarm 4.5V 7.1V 8.0V 12.6V
Absolute Worst Case 9.0V 9.0V 16.0V 16.0V
7
Audible Alarm T ones
For wrist strap malfunctions the
Model 724 monitor indicates a
different tone for each operator-a
continuous tone for #1 operator and a
fast chirping beep for #2 operator. The
volume of the wrist strap alarm is
adjusted by selection of the internal
DIP switch #1. For work surface
malfunctions, a slow chirping beep is
made. This alarm sound is turned on
or off by selection of DIP switch #2.
Switch #1 and #2 are accessible
through a slot located in the bottom of
the chassis.
Fig. 4 - Selected desired alarm options
Work Surface Monitoring
The Model 724 monitors its
connection to ground and the
grounding of a 3M ESD work surface.
A loop resistance is measured from
the monitor, through a 3M™2380
Monitor/Table Mat Cord to the work
surface (Section 2), across the
conductive layer of the work surface,
through the grounding wire of the
work surface to an electrical ground
and finally back to the monitor through
the 724 grounding wire. If the
resistance of the loop exceeds
3.7 Megohms* the work surface high
red lamp (M) will illuminate and all
green lamps will be extinguished. If
DIP switch #2 is in the ON position
(Fig. 4) the audible alarm will activate.
If no ESD work surface is to be
monitored, the 3M 2380 Monitor/Table
Mat Cord and the ground wire of the
724 must be connected to an electrical
ground (Section 3). This is done to
ensure that the 724 is providing a
ground connection for the operators.
Again, if the loop resistance exceeds
3.7 Megohms the work surface high
red lamp (M) will illuminate and the
alarm will activate if selected.
Caution
The grounding wire from the work
surface and the ground wire from
the Model 724 monitor must be
attached to separate electrical grounds.
The work surface monitoring function
is active any time that the power supply
for the monitor is plugged in.
Caution
Disconnect the 3M 2380 Monitor/
Table Mat Cord to prevent possible
damage to the Model 724 monitor
before testing the resistance of the
work surface with a high voltage
megohmmeter.
* Resistance values are ±15%
DIP Switch
Switch #1
Loud
Switch #2
On
Model 724 Bottom View
Soft
Model 724 bottom view
DIP switch
Off
On
Loud
Switch #2
Switch #1
Loading...