| 摘要 |
A radio alarm system generally comprises a transmitter, 12, a receiver, 14, and/or a combined transmitter and receiver 10, and a wireless detecting means 20 including no power supply. The transmitter is located at one area of a structure for continuously transmitting a radio signal to establish an electromagnetic field therethrough. The wireless detecting means 20 comprises a receiving unit 30, a detecting unit 40 including a detecting element 44 connected in parallel with a normally closed vibration switch 46, and a transmitting unit 50. Upon the occurrence of vibrations exceeding a predetermined intensity, the normally closed vibration switch 46 is caused to open, producing a voltage across the detecting element 44, which voltage is impressed on to the original potential and resonated through a resonant circuit 52, 54, 56, through which a frequency multiplied warning signal is transmitted to the receiver to trigger an alarm device. <IMAGE> |
