"The object of this program was to extend the capabilities of visual paging systems both in size and functions in mines. The system developed uses the mine pager phone line for communication, monitoring, and remote control. A central station, using a minicomputer, transmits signals by phase inversion modulation of a 16,384-hz carrier to as many as 999 remote units. The remote unit addressed returns an echo to indicate that it is functioning and, in the case of monitor units, to convey the monitor data. Magnetically latched display disks, which can be seen from both sides when posted, are used for visual paging. Lists of the addresses of posted pages, unanswered pages, and nonechoing units are prepared by the central station computer. The system was designed to be intrinsically safe and should operate for 3 months on a 12-volt lantern battery." - NIOSHTIC-2

NIOSHTIC no. 19801001

National Institute for Occupational Safety and Health

contract J0177020