SCS 725 – Portable Wrist Strap Monitor

The SCS 725 Wrist Strap Monitor is designed to monitor the operation of a wrist strap grounding system for a single operator. This product has been designed and tested for use with SCS Dual-Wire Wrist Straps and SCS Worksurfaces Grounding Systems. This unit is powered by a 9 volt alkaline battery. Use of other components or use in any other application not evaluated by SCS may cause improper performance and/or an unsafe condition. To avoid damage to the 725 Wrist Strap Monitor, do not use this monitor outside of the operating conditions listed in this user guide.

The SCS 725 Wrist Strap Monitor monitors the battery voltage and alerts the operator when it is necessary to change the battery. When the battery voltage falls below 6V +/- 10%, the red lamp will illuminate with no audible alarm. At this time the SCS 725 Wrist Strap Monitor is still operational, making reliable resistance measurements of the wrist strap assembly and the ground connection.

The SCS 725 Wrist Strap Monitor performs a resistance measurement by applying a small electrical current. 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 wristband, through the skin of the wearer under the band, through the second side of the wristband, 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, the wrist strap ground cord, wristband, and the interface of the wristband 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 SCS 725 Wrist Strap Monitor 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 725 Wrist Strap Monitor. 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.