Alarm signaling systems - principle of operation

Principle of operation

The most basic alarm systems as a principle of action is very similar to the operation of an electric light bulb - something happens when you close or interrupt an electric circuit. In one case the bulb is lit or extinguished in the other - the control panel of the alarm system activates the alarm or cancel event.

Modern alarm systems are a closed loop in which the control panel register event considering the change in resistance when a sensor is activated / deactivated.

Ultrasonic sensors operate by sending a constant stream of undetectable to the human ear, sound waves in the frequency range of 25 to 75 KHz and captures the reflected ones. Sensors react to the change in frequency of sound waves that change from movement of objects. Hard surfaces (floor, ceiling, walls) generally reflect the majority of ultrasonic energy, while other objects absorb most of it. When objects are stationary, the frequency of transmitted and received back energy is the same. However, if the frequency changes, the sensor generates an alarm signal.

Microwave sensors have transceivers for microwaves. The receiver works either with reflected waves or by sensing a difference in the intensity of the beam. Generating energy in the microwave range of the electromagnetic spectrum, the sensor operates as an active volumetric device that reacts to changes in frequency (Doppler effect), change in phase of frequency or energy received back the that occurs as a result of movement of the object.

An alternative may be sensors with photo cells. In them we have two components - a source of targeted light and light sensor to which the source sends the light beam. When someone passes between the source and sensor, the sensor senses the difference in the level of illumination and records event.

PIR (passive infrared) detectors operate capturing infrared heat energy radiated from the body of the offender. In normal mode, they monitor constantly the levels of infrared radiation and react if these levels change very rapidly. The term "passive" in this case indicates that this type of detectors can operate without having to generate and radiate its own energy (unlike ultrasonic and microwave sensors).

Acoustic sensors are another variant of the detectors, which are used as mounted near the glass or the glass itself. When the glass is broken, sound is generated in a wide range of frequencies. The sounds may be below 20 Hz and above 20 KHz (infrasound and ultrasound), but also in perceived by the human ear range between these 2 frequencies. In most cases, sound is produced in the range of 3 to 5 KHz for which these sensors are listening.

Once the sensor alerts the control panel, it activates an alarm in the area and remembers the event associated with the zone for future reference.

Once activated the alarm and, according to Control Panel settings, it can be deactivated by entering the code associated keyboard or automatically after a specified time interval. If the system is connected to a transmitter of a security company, the control panel sends alarm signal to the transmitter and it notifies security teams.

Maintenance of the various settings in areas such as the guarded perimeter, allows the area, which is associated with the front door to behave differently than other areas - such as an alarm when it is activated with some delay, which allows the user to revoke an introduction of a code from the keyboard, while other areas cause immediate alarm.