3M 724 Instructions Manual - Section 1.
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
µ
A
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%