Motion Sensors By Elva S. Agbon ICS 30 B MOTION SENSORS A sensor specifically designed to detect a gentle or sharp up and down or side to side motion of the vehicle. Used for security and for a variety of non-security functions such as monitoring seismic activity or to examine the flow of a production line to identify potential equipment malfunctions. They are activated by the vibrations of breaking glass, the motion of an approaching car, a person’s body heat, or even changes in humidity or barometric pressure Purpose: to detect the presence of some ‘body’. Dual Technology Motion Sensor The dual technology motion sensor utilizes two different types of technology, PIR and microwave technology. Microwave technology picks up any movemen within the range of the microwave sensor, whereas PIR only picks up heat movement. Microwave PIR sensors alarm upon valid signals from both the PIR and the microwave sensors. This gives these sensors greater reliability and makes them less likely to trigger a false alarm from environmental disturbances. These devices require accurate adjustment for proper operation. Passive-Infra-Red Motion Sensor Passive-infra-red (PIR) motion sensors are used to protect large open areas from intrusion. The PIR sensor protects the designated area by creating fields and zones of infra-red light that detect heat and motion. The PIR is the most popular detector in most alarm systems. Physical limitations to the PIR technology a brick wall that is struck by the sun during some part of the day. The brick (cement, close neighbor etc.) wall, becomes hot, and even a human moving in front of it is not as 'noticable' as the background heat of the wall. depending on the 'apparent background', they may take 'some time' to detect motion. ‘LOGIC’ of the PIR sensor The ‘logic pf the PIR sensor is that it must detect ‘significant change’ of the normal level of heat within the ‘field’ of its view. The circuits that control must be able to determine what ‘normal’ is, and then close a switch when the normal field changes, as when a human walks in front of it. It must also be able to ‘tolerate’ slow changes within the field, and remember that as the new ‘normal’. This is so that gradual changes like the sunlight changes throughout the day don’t cause a false alarm. This is a standard behavior of ‘PIR’ type sensors. Common types of the PIR sensor 1. Hawkeye Quite small, it is cheap(often a freebie), it can be very useful. A very good indicators of ‘someone walking thru the doorway’. Cont.. 2. DM10A It is much larger than the Hawkeye, and not very attractive. It does however have larger batteries, and better range of ‘field’, as well as transmitter distance. It never sends an OFF command, but does send an ON command every 25 seconds or so as long as motion continues. Example: Area Sensor An outdoor motion sensor detects a ‘warm’ body moving across an area. It automatically turns on the lights, and sends a message that announces the event. The most frequent use of the PIR sensor There are two events: 1. Local Event. It would be one like someone stepping on a floor mat which had a contact switch in it, walking through a light beam, or driving a car over a magnetic sensor. 2. Area Event. It would be someone moving within the ‘field of view’ of a particular sensor. This area is generally known or controllable, but it is large in comparison to the ‘field’ of a contact switch etc. Fresel les Some sort of plastic ‘lens’ that covers the circuit board and the PIR sensor device. It ‘pinches light that passes thru it. Tends to ‘pinch’ the light such that it is horizontally sensitive. This means that the lens/PIR will be more sensitive to motion of a warm body, horizontally ‘across the field of view’.
