Patent ID: 6831550
Filing Date: 2004-12-14
Classification: G04G,G08B

Abstract:
A security system using sensors comprising:multiple surveillance terminals each equipped with a clock and adapted to send security and other data over a power supply line; and a surveillance center for performing security surveillance utilizing security data received from the surveillance terminals, wherein: at least one surveillance terminal among the multiple surveillance terminals uses the power supply line to send a time calibration signal to required ones of the other surveillance terminals at appropriate times, the surveillance terminals receiving the time calibration signal use the signal to correct their clocks to eliminate time error among the clocks of the multiple surveillance terminals, each surveillance terminal uses the power supply line to send to a prescribed surveillance terminal time-stamped data created by adding to the security and other data it sends send-time data indicating the time at which the data was sent, and the prescribed surveillance terminal discriminates operating states of the surveillance terminals by comparing receive time and send time of time-stamped data.