MAN-DOWN ALARM SENSOR SYSTEM FOR PERSONAL ALARM RADIO TRANSMITTERS

Publishing Venue

Motorola

Related People

Abstract

Man-Down sensors used in Personal Alarm Transmitters or Transceivers use mercury switches to sense the body motions of the person wearing the unit. The mercury in the switch capsule is continually making and breaking contact as the person wearing the unit goes through normal day to day body motions. The man-down circuitry integrates the constant making and breaking of the mercury contact only producing an output when the circuit is open for a fixed period of time, approximately 5 to 10 seconds. The time constant is compromise between the desire to alert the central station as soon as the event occurs and desire prevent false alarms from normal body motions.

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MOTOROLA Technical Developments Volume 8 October 1988

MAN-DOWN ALARM SENSOR SYSTEM FOR PERSONAL ALARM RADIO TRANSMITTERS

by John Stahl and Rob Sapashe

   Man-Down sensors used in Personal Alarm Transmitters or Transceivers use mercury switches to sense the body motions of the person wearing the unit. The mercury in the switch capsule is continually making and breaking contact as the person wearing the unit goes through normal day to day body motions. The man-down circuitry integrates the constant making and breaking of the mercury contact only producing an output when the circuit is open for a fixed period of time, approximately 5 to 10 seconds. The time constant is compromise between the desire to alert the central station as soon as the event occurs and desire prevent false alarms from normal body motions.

   False alarms cause the user to loose confidence in the system as well as cause a disruption in plant opera- tion, for example when the alarm sounds the plants hazardous materials team may respond or the local am- bulance squad is alerted. The "cry wolf" problem can be so severe that the system will be turned off.

   The circuit described below adds a PRE-ALERT TIMER and an AUDIBLE ALARM to the Personal Alarm unit. The Pre-alert Timer and Audible Alarm gives the wearer time to cancel the alarm if he or she is not in danger. If for example, you drop a screw driver and it rolls under the desk. While you are trying to find the screw driver, the Man-Down circuit is...