The intrusion detection system is the solution to protect your building and its surrounding from intrusion, theft, hold-up, illegal occupation, kidnap, hostage taking, vandalism, sabotage and many other intrusion intentions. In its widest sense, the term covers all types of criminal act. The solution is a comprehensive package of devices, controllers and organizational measures to enable automatic detection of unauthorized entry. When an intruder is detected it is important to initiate appropriate silent or clearly perceptible measures in a timely manner to prevent loss.
Structure of an intrusion detection systemThe automatic intrusion detection system detects any attempted intrusion by sensing associated phenomena including changes of shape, position or pressure, motion, structure-borne or room noise, changes in temperature, etc. The hazard level is automatically determined on the basis of preset parameters and appropriate measures are initiated in the form of alarm and control functions. Every intrusion detection system must be based on a protection concept. This contains all the individual measures needed in order to achieve the desired protection objectives. The aim should be an effective combination of mechanical protection and electronic surveillance. If the types of threat are not known, they must be identified as part of an appropriate risk analysis. For each type of threat identified, a protection objective must be defined in order to mitigate the risk and determine an effective surveillance concept.
Putting aside the physical differences in detection principles, there are essentially two different types of intrusion detector namely “passive” and “active” detectors.
Passive detector systems
These operate purely as receivers. Using an appropriate sensor, a passive detector can register the occurrence of or change in certain physical values and detect this as an alarm situation. The basic physical values that exist within the sensors perception range under normal conditions, represent the reference point for alarm detection. The more stable these basic values are, the less risk there is of spurious alarms. The useful signals are usually weak and this generally means a high standard of evaluation is required. Account is taken of environment-induced changes by means of filtering and in some cases by adjusting the response sensitivity.
Examples of passive detector systems:
- Passive infrared motion detectors
- Seismic detectors
- Vibration detectors
- Picture monitoring systems
- Glass break detectors
- Acoustic detectors
- Contact detectors
Active detector systems
These operate with a transmitter and a receiver. An active detector system consists of a transmitter part which generates a defined signal in an electronic circuit and transmits it and a receiver part which receives and monitors the transmitted signal and detects changes as a serious situation. Comparing the transmitted and received signal provides additional parameters and as a result, active detector systems have better alarm detection properties and additional means of avoiding spurious alarms. Environment-induced interference is eliminated by filters. Transmitter and receiver can be housed in the same or in separate devices.
Examples of active detector systems:
- Ultrasonic detectors
- Light barriers
- Microwave detectors
- Field change detectors
- Capacitive detectors