Motion detection has become an essential ingredient in traditional electronic security and now it is being utilized in access control and video surveillance systems. With more applications and so many different uses, can there be too much of a good thing? It seems the motion sensor is always the device getting the bad rap. However, an understanding about how these devices fit best in your installations will help them to be less prone to scrutiny.
Motion sensing technology has made huge advances since the introduction of PIR (Passive InfraRed) and MW (MicroWave) technologies. Before the introduction of PIRs and MW sensors, interior protection was attempted with devices such as photoelectric beams and ultra-sonic detectors. Beams created a threshold by sending a light beam to a receiver. They were monitored for interruptions in the beam. Ultrasonics emitted high frequency tones and then would measure for distortion or delayed reflections of the signal. Changes in the reflectivity of the protected area signaled an intruder.
While early ultrasonic and photoelectric beam technologies were relatively primitive and inherently prone to false alarms, dealers had nothing else to use for many installation situations. For example, back in the day, photoelectric beams were popular for flat roofs of commercial buildings, and ultrasonics were just the thing for large, harsh environments such as factories and garages. Unfortunately, roof tops are frequented by birds and other flying objects, and industrial spaces are home to equipment such as pneumatics and steam heating. All of these objects can generate false alarms.
Though there is still merit to both of these technologies , there are others from which the installer can select for the most appropriate method of providing protection.
When they first appeared, PIRs and MWs represented a major breakthrough for the alarm industry. The technologies have been combined, and the sensing and signal processing have been refined. The variety of selection has increased, making motion detectors and sensors more affordable and deployable for more applications .
Avoiding Problems
In practice, false alarms are the result of a number of issues including user error, poor application engineering, power surges and lightning, and faulty equipment. Of course, it is no surprise if you choose a substandard motion detector, false alarms result. Some dealers also instruct the central to dispatch on undefined signals (or neglect to instruct the central to log only), in case they are legitimate alarm signals which have been garbled during transmission.
In the Security Dealer March 2006 feature, “KEYWORD: SECURITY,” Randall Wang’s analysis indicated that 75% of his company’s false alarms were being caused by the motion sensors. Although initially startling, alarm dealers probably do not find that number that hard to believe, given the large numbers of motion sensors you deploy.
Although many manufacturers make high quality motion sensors, experienced dealers, looking for the latest and greatest features in order to remain competitive, are still somewhat cautious about jumping on the bandwagon when something “revolutionary” appears on the market.
the Inner Workings
• Detection Zones: Typically PIRs utilize a Fresnel lens, the exact characteristics of which determine the detection pattern of the particular device. Some PIRs are supplied with a few lenses so that the installer can select the one which best suits a particular installation. Lens masking is also a typical technique used by installers to control the areas within the PIR’s field of view. Such masking could prevent the PIR from ‘seeing’ a source of heat or light within the protected area which might otherwise create false trips.
• Pet Immunity: A signal processing feature offered in some motion sensors that ignores heat source “signatures” typical for specific size animals. This allows the PIR to be deployed without masking off zones or avoiding furniture or areas where the family pet might normally go.
• Alarm Display Walk Test LED: During the installation setup, the walk test LED tells the installer the exact detection pattern of the detector. In some situations, it is okay to leave this LED active because the client knows the PIR is working. However, in certain instances, indicating the detection pattern might give an evil doer a clue to blind spots of a detector and an uninvited intrusion.
• Pulse Count: A signal processing feature, it can be used to adjust the detector to suit the environment without having to mask off zones or reduce sensitivity. If drapes of foliage are within the detector’s range, increasing the pulse count will prevent slight movements from triggering an alarm.
• Insect-Proof Housing: Indoor or outdoor detectors are subject to invasion, contamination and environment, all of which can cause obstruction of the optics or short circuits on the PC boards.
• Alarm Memory/First-to-Latch: A feature useful in multiple detector installations to determine the path of the intruder or the source of the false alarm.
• Automatic Temperature Compensation: Because PIR’s measure relative temperature (infrared energy) between the background and a subject, and since the body temperature of a subject will remain relatively constant, the room temperature may vary greatly; motion sensors that do not have temperature compensation will be more sensitive when the room is cooler, and less sensitive when the room is warmer. Automatic Temperature Compensation stabilizes the detector’s sensitivity.
• RF/Static/Surge Immunity: An electronic security alarm is a complex system. Each element of the system is subject to RF/static and power fluctuations. If reliability and false alarm reduction are important to you, then select motion detectors which offer this feature.
• Selectable Walk Detection Speed: With all the false alarm suppression features in a motion detector—and the wide variations in deployment—you might inadvertently numb your detector to the point where it will not detect. Walk detection speed is another feature you can use to fine tune the detector to suit the job.
Strategic Deployment
Motion detectors are tools. The skilled security professional will select the appropriate detector; install it properly, and provide the desired levels of protection without contributing to the epidemic of false alarms. The use of dual technology detectors provides excellent detection while reducing false alarms significantly. Thoughtful deployment of motion sensors is essential for proper operation.
• PIRs: The most frequently deployed form of motion detector. They have evolved into a cost effective and reliable security tool, successfully deployed in both indoor and outdoor applications. PIRs are used for security, lighting control and door control applications. Many innovations in the PIR technology constantly improve the level of performance of PIR products.
• Dual Technology: These devices usually incorporate PIR and microwave. PIRs detect movement of warm objects against a background level; microwave sensors transmit a signal, then analyze the reflected signal. Since PIR and microwave operate in different portions of the spectrum, and one uses passive sensing and the other active; they are not subject to the same false alarm sources but are nepenthes subject to possible false alarm issues. If improperly deployed, a dual detector can be double trouble. For example, if the detector logic is set to a logical “OR,” then the detector will alarm if either section senses motion. Microwave sensor range is not limited by walls; they see right through them, so activity outside the structure might be detected as an intrusion. Similarly PIRs will react to a variety of non alarm stimuli.
• Video Motion Detection: Digital video signal processing has fostered a new approach to motion detection, video motion detection. The surveillance camera may become the basic motion detection component for security systems of the future. By combining video cameras with advanced signal processing, new levels of surveillance are achieved to help provide security in airports and public places which are now targets in the new homeland security efforts.
• Access Control: Motion sensors have found applications in door and access control applications as the demand for access control has increased in response to the public’s demand for security. Motion detector technology is filling this need with a variety of devices.
• Outdoor Motion Sensors: Have long been considered unfeasible because detectors were not available with the ability to adequately discriminate between real targets and nuisance events. By combining detection technologies and advanced signal processing such as Doppler and other advanced signal processing, motion sensors are now capable of performing in outdoor environments.
