The link method makes use of the fact that interrupting the transmission path between the transmitter and receiver results in changes to the strength of the received signal. It can thus determine the presence or absence of an intruder. It is used for intrusion alarm devices and radio wave switches.
When the signal is blocked, reception level will decrease. How much of the signal gets through will depend on the size and consistency (material) of the intrusion: the larger and denser the intruder, the more the level will fall.
The transmitter and receiver face each other. The 1st Fresnel zone is the main path between them. However, it is also necessary to take into account the 2nd Fresnel zone to determine what may affect the path between sensors.
Mutual multipath interference can result in either strengthening or weakening of the signals. It is said that one opposing link sensor (fixed installation) is susceptible to such interference.
To mitigate the weakness of these link sensors, we recommend a multilink approach, in which a link line is made up of multiple transmitters and receivers. Among the products we offer are sensors that employ the PLL method, ensuring high frequency stability. Monitoring lines composed of interlinked sensors ? transmitters and receivers ? will have multiple paths for high reliability: when several of these lines are interrupted, an intrusion alert will be output.
