Electronic intrusion detector sensing people or objects - has two wire line connected with oscillator and phase changer to resonate with frequency varied by intrusion

摘要

The appts. detects a change in an environment, particularly due to the intrusion of an object or person. A line of two conductors is powered by an oscillator connected by a bipolar connection to one of its ends. An adjustable phase changer has its input connected to the other end of the line, and its output connected to a synchronisation input of the oscillator. A discriminator circuit has its input connected to the oscillator output, and at its output produces a difference signal with an increased amplitude. This signal is the difference between the value of a frequency parameter of current produced by the oscillator frequency parameter of current produced by the oscillator and a reference value. A loop is formed by the phase changer, oscillator and line, having a resonant frequency which is affected by an intrusion.