INTRODUCTION
The evolution of motion sensors dates back to the evolution of man. It is said to have used by man to calculate the movement of stars to determine the best crop-growing season. Motion sensors gained their popularity during the World War II. The significant increase in demand for detection and monitoring during the World War II generated technological advancements in motion sensing. Radar, which was invented several decades earlier, was being fully developed during the war, to detect the motion of aircrafts. Although the development of radar systems was a great leap forward, it was limited only to military use. The first application of motion sensing outside military use was an ultrasonic alarm. This was developed by Samuel Bagno in the mid-1940s. The ultrasonic alarm worked similar to that of radar. It created a “web of ultrasonic waves inside a room” and detected the motion of a person. The detector worked by spinning a web pattern from the waves coming from inanimate objects in the room and returned to receiver. Movement shifts created disturbances in the pattern and triggered an alarm. The way in which motion sensors work, typically depends on the type of sensor being used and on the device that uses the sensor. Two basic types of motion sensors are Active Sensors and Passive Sensors. Active sensors emit a signal, typically a burst of waves that is emitted from the surrounding. The sensor will receive the reflected signal and an alarm will be triggered or any necessary actions. On the other hand, Passive sensors do not emit signals, but detects IR radiation around the sensor.
Ultrasonic sensors were not very accurate, as they could trigger false alarms. They trigger alarms at the ringing of a clock alarm, phone ring or coming up of heating system. Hence, an alternative technology was required. The invention of ultrasonic alarm created demand for other non-military application, especially infrared technology. Although infrared technology existed since mid-1800s, limited to astronomical purposes, infrared sensors were being developed to a full scale at the same time as ultrasonic sensors. IR sensors operate on the presence of human heat present in their field of view. They are passive sensors. Unlike radar and ultrasonic sensors, IR sensors just receive signals but do not emit. They discern human movement by detecting incident IR radiation, which varies in proportion to the temperature difference between human body and surrounding surfaces. They can distinguish between the thermal signals emitted from human body and those emitted from other objects in the environment. However, passive IR sensors cannot detect motionless objects. They cannot accurately determine the direction of motion nor create any thermal images.
HOW DO MOTION SENSORS WORK?
There are two basic kinds of motion detector sensors. They are categorized based on how they detect motion. The first type is called active sensor. Active sensors emit energy, usually ultrasonic sound waves, into immediate area. They are sometimes called radar-based motion detectors. Passive sensors do not emit energy, but instead read changes in the energy, in the surrounding area.
Active motion sensors work by sending out bursts of ultrasonic sound waves, after which the sensor waits for the energy to be reflected back. Active motion detectors are created with sensors that will send an alarm signal in the event that the pattern is disturbed. Passive sensors are also known as Passive Infrared (PIR) sensors because they detect and measure incoming infrared energy. They are sometimes called as pyro electric detectors. Most PIR sensors can detect emissions in the range of 8 to 12 micrometers. They operate with the help of a photo detector. The photo detector converts light in these wavelengths into an electrical current, which is run through a tiny computer housed in the unit. The alarm is triggered when the photo detector detects large or fast variations in the distribution of the emitted infrared energy.
MICROWAVE MOTION DETECTORS
Microwave motion detectors are different from PIR based sensor systems. They transmit energy and look for a frequency shift (similar to Doppler), due to motion in the covered area. The microwave motion detector sends out high frequency radio waves and then detects the level of energy reflected back to the device. If the radio frequency hits a moving object, the frequency changes and motion detector is activated. Microwave motion detectors often trigger false alarms as they can penetrate through walls. Hence, this is not the most reliable motion sensor system in use. Therefore, normally microwave based motion sensor systems will be used in conjunction with Passive Infrared motion sensor systems. They are called dual technology motion sensors and will not activate until unless both technologies detect motion. Microwave based motion sensors are similar to radar-based motion detectors, except for the energy waves used for motion detection.
RADAR BASED MOTION DETECTOR
An automatic door opener is a good example of radar based motion detector. The box above the door sends a burst of microwave or ultrasonic sound waves and then waits to receive the reflected energy. If there is no one in front of the door, the wave pattern will be reflected the same way as transmitted. However, when there is someone standing in front of the door, the reflected wave pattern will have a disturbance, which will be sensed by the sensor and the door will open. In a security system, the sensor will send an alarm signal, when there is a disturbance in the reflected wave pattern. These sensors cover a larger area than IR sensors, can penetrate through walls and reliable over a longer distance. Still they are least popular because of their electrical interference and their cost.
PHOTO SENSOR MOTION DETECTOR
This kind of motion sensors will be found often in shopping malls. It includes two components namely a source of focus light, which is normally laser and a light sensor. In home security systems, the beam of light source will be aimed at the laser source. When someone walks through this path, the path of the beam will be blocked briefly. The drop in light levels will be registered and signaled to the control box.
INFRARED MOTION SENSORS
They are the cheapest and most reliable system of motion sensors, otherwise called as Passive Infrared (PIR) sensors. These sensors use infrared light spectrum to measure the heat of objects that pass through their path and compare it with the temperature of the surrounding objects, such as a wall. If the temperature is significantly higher than the surrounding objects, the sensor will trigger an alarm. It can be used to monitor a specific area only at a time. However, several sensors can be fitted with different lenses to cover a larger distance. Most of the PIR sensors are advanced to automatically adjust to changing ambient temperatures. They often differ in their detection pattern and range, but always made up of a number of sensitive beams.
DUAL TECHNOLOGY SYSTEMS
Dual technology systems use a combination of infrared and microwaves to provide most complete coverage possible and reduce the occurrence of triggering false alarms. Both types provide their advantages and disadvantages. It allows the users to alter sensitivity in houses that has pets.
ACTIVE INFRARED
In AIR based motion sensors, an IR emitter sends an IR beam, which will be received by a receiver. When the beam is interrupted, a motion is detected. Due to the way they are implemented they are less prone to false positives. Their main disadvantage is detectability; they can be easily “seen” using a regular camera or any IR detection mechanism. In some cases, they might be possible to avoid if only door to a room is monitored. The adversary can detect the source of the beam and find the receivers, and then emit a beam on their own. Some AIR based motion sensors emit IR in a pattern of a certain frequency to make it difficult to replicate. However, the adversary can learn that pattern and replay it to the receiver.
INTERNATIONAL STANDARD FOR MOTION SENSORS
There are a variety of position sensors and each type has different standards. Position sensors are widely divided into two groups as contact devices and non-contact devices.
CONTACT DEVICES
- Limit Switches: Limit switches are electromechanical contact devices. Applicable standards will be discussed as follows:
- IEC 60947-5-1: This standard explains the general rules relating to low-voltage switch and control gear for industrial use. Objective of this standard is to state the characteristic of control circuit devices, electrical and mechanical requirements and functional requirements to be satisfied. IEC 529 rates the level of protection provided by enclosures, using an IP system.
- EN 50041 and EN 50047: They come under CENELEC (The European Committee for Electrotechnical Standardization) which defines characteristics and dimensions of limit switches. These standards relate to low-voltage switch and control gear for industrial use. They also define the operating point to various head actuators, earth terminal requirement, terminal marking and minimum degree of IP protection.
- NEMA (National Electrical Manufacturer’s Association) rates the protection level of enclosures as IEC 529, but includes tests for environmental conditions such as rust, oil, etc., which are not included in IEC 529.
- Resistive Position Sensors: They are also called as potentiometers or simply position transducers, which were primarily used for military applications. They are passive devices. Standards for position transducers are:
- The Variable Electronics Component Institute has developed a number of testing and performance standards for governing potentiometers. When their standards are not binding on the manufacturers’, they help ensure practical, meaningful and consistent methodologies.
- MIL-STD-202F: Many potentiometers also conform to military standards. This standard establishes uniform methods for testing electrical and electronic components, including basic environmental tests to determine resistance to deleterious effects of natural elements and conditions surrounding military operations, and physical and electrical tests.
- IEC 60947 is used for other position sensors namely magnetic sensors, ultrasonic sensors, proximity sensors, photoelectric sensors.
EUROPEAN STANDARD (VdS 2312en: 2010-12 (04))
These guidelines include minimum requirements and test methods for motion detectors with volumetric monitoring characteristics in classes A, B and C. These guidelines shall be applied in conjunction with the “Guidelines of Intruder Alarm Systems, General Requirements and Test Methods”; VdS 2227 and the “Guidelines for Intruder Alarm Systems, Protection against Environmental Influences, Requirements and Test Methods”; VdS 2110. These guidelines also apply to intruder detectors, which use similar technologies like motion detectors but have different monitoring characteristics. These guidelines contain the requirements and test methods of the European Standards DIN EN 50131-2-2, DIN EN 50131-2-3, DIN EN 50131-2-4, and DIN EN 50131-2-5. This means that, if motion detectors comply with the requirements of European Standard of higher grade, they must also fulfill their additional requirements.
CLASSIFICATION
The performance criteria for different classes are defined in the “Guidelines for Intruder Alarm Systems, General Requirements and Test Methods”, VdS 2227. An alignment of the security grades from the standard series EN 50131 is also made. The environmental classes are set in accordance with VdS 2110. Depending on the class, the requirements on the function may differ. The matrix indicating different functions and requirements are as follows.
1,2,3,4 VdS requirement corresponds with the requirement of shown grade of EN 50131-BWM
- VdS corresponds with the requirement of EN 50131- BWM without grade dependent differentiation
Op2 Optional for the fulfillment of shown grade EN 50131-BWM
Op3 Example: Op2 requirement is valid optionally for the fulfillment of grade 2 of EN 50131-BWM
VdS requirement exceed the respective requirement of EN 50131-BWM
VdS Additional VdS requirement without equivalent in EN 50131-BWM
NA Not Applicable
a Wired
b Wire-free
EN 50131
This standard specifies the requirements, performance criteria and testing procedures for controlling and indicating equipment intended for use in intrusion and hold-up alarm systems. It specifies the requirements for CIE installed in buildings using specific or non-specific wired interconnections or non-wired interconnections. These requirements apply to ACE installed inside or outside the supervised premises and mounted indoor or outdoor environments. This standard specifies performance requirements for CIE at each of four security grades identified in EN 50131-1, “Alarm Systems-Intrusion and hold-up systems- System requirements”. This standard includes mandatory functions, which shall be provided on all CIE for appropriate security grade, as well as optional functions. It does not deal with requirements for compliance with EU regulatory Directives.
USES OF MOTION SENSORS
- Cellphones with motion sensors: The motion sensors used in mobile phones are accelerometers. They are complex motion sensors. This sensor translates motion into action on the screen. They are used in tablet computers and digital cameras to display the images in upright direction.
- Motion sensors in gaming: Motion sensing is an emerging technology in gaming. Microsoft’s Xbox360 Kinect peripheral is the first demonstrator for touch free motion sensing. It facilitates advanced posture, gesture, facial and voice recognition.
- Lighting Control: Motion sensors are often used indoors to control electric lighting. If no motion is sensed, and then the space will be considered vacant, thus it need not be lit. This can help in saving substantial amount of energy.
- Motion sensors for touch less applications: Motion sensors are used for a variety of touch less or gesture technologies depending on the technical approach to measure motion. Some of the gestures include writing messages or composing mails in air, operating computer without touching it, navigate through devices by just pointing it, etc. These are some of the most advanced applications of motion sensors.
- Motion detector lights: Most popular use of motion detectors is in lighting. They may be used in many places, but their singular purpose is to light up dark places. It is very helpful in outdoors to prevent trespassers from hiding.
- Motion detector cameras: This application is comparatively recent to home security industry. Though some motion detector cameras are fixed in a place to monitor activities in a specific area, others can be easily moved from one place to another.
- Motion detector alarms: This is the oldest application of motion sensors. They trigger an alarm when a difference in the wave pattern is sensed or a difference in temperature is observed in their range of view.
- Motion detection and control using passive IR technology: It is used in lighting controls, access control, display systems and general-purpose proximity applications. It is also an easy way to add energy management capability to various applications. It can operate in serial mode and hardware mode.
- Array sensors: Instead of single thermal sensing element in most of the passive IR sensors, recent sensors employ an array of IR sensing elements to measure actual temperature as well as temperature gradients within 600 viewing area. These array sensors can simultaneously detect direction of moving object and people in all directions. Its co-ordinated array of sensors can even detect multiple objects and people at the same time. They can even detect hand movements from simple gestures.
- Multifunctional MEMS: Micro-Electro-Mechanical Systems (MEMS) and thin film technologies enable the integration of microelectronics circuits and multifunctional sensor arrays fabricated on silicon substrates for detecting multiple parameters. Such integration facilitates to reduce the cross-links between adjacent sensors.
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