Motion Sensors

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Motion Sensors

• By Elva S. Agbon
• ICS 30 B

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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
  persons body heat, or even changes in humidity
  or barometric pressure
• Purpose to detect the presence of some body.

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Dual Technology Motion Sensor

• The dual technology motion sensor utilizes two
  different types of technology, PIR and microwave
  technology. Microwave technology picks up any
  movement 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.

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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.

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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.

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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 dont cause a false alarm.
  This is a standard behavior of PIR type
  sensors.

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Common types of the PIR sensor

• Hawkeye
• Quite small, it is cheap(often a freebie), it can
  be very useful.
• A very good indicators of someone walking thru
  the doorway.

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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.

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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
• 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.
• 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.

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Fresnel lens

• 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.