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1. Verification Procedure for the 3M Wrist Strap Monitor Model 725

Wrist Strap

Monitor Model 725

Figure 1 – 3M

Wrist Strap Monitor Model 725 with 3M

SECTION 1

Theory of Operation

(Refer to Figure 1)

The 3M

Wrist Strap Monitor Model 725 is designed to monitor the operation of

™

the wrist strap grounding system of a single operator. The system features special

wrist bands and ground cords that contain two independent conductors.

The Wrist Strap Monitor Model 725 performs a resistance measurement by

applying an electrical current of less than 1 μA. The path for the current is through

one conductor of the wrist strap 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 wrist

strap ground cord that contains a current limiting resistor, and finally back to the

monitor. If the resistance of the wrist strap loop is less than 35 megohms

strap ground cord, wrist band, and the interface of the wrist band to the arm of the

wearer are considered to be functioning correctly. If the measured resistance is over

35 megohms

, a red lamp flashes along with a chirping audible alarm.

In addition, the Wrist Strap Monitor Model 725 monitors the ground clip

connection to a predetermined electrical ground. This is accomplished by

measuring the resistance from the monitor, through one conductor of the monitor's

ground cord and metal clip, through the ground point conducting medium, through

the other metal clip and conductor of the monitor's ground cord, and finally back

to the Wrist Strap Monitor Model 725. If the resistance of this loop exceeds 10

megohms

, a red lamp will illuminate with a continuous audible alarm. This

***

indicates that there is a problem with the monitor's ground cord or the ground

point connection.

*3M

Dual Conductor Cord & Wrist Band are required for use with

™

the 3M

Wrist Strap Monitor Model 725, ordered separately.

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Dual Conductor

Metal Wrist Strap*

Dual Conductor Wrist Strap Assemblies.

Dual Conductor

Fabric Wrist Strap*

, the wrist

** Resistance values are ±15%

*** Resistance values are +15%, -50%