Transcript Sensors

Chapter 8
Alarms: The First Line of Defense
Sensors
The Eyes & Ears of the
system
© 2001 National Burglar & Fire Alarm Association
8-1
Perimeter Sensor
Objective
• To Detect an Event.
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An Open Door.
A Broken Window.
Entry Thru Wall, Roof or Floor.
Entry Thru Outer Perimeter.
© 2001 National Burglar & Fire Alarm Association
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Perimeter
• The perimeter is the outer reaches of a
system.
• For a building system it is the walls,
floor and ceiling.
• For an outdoor system it is a fence or
perhaps the outer edge of the sensors
pattern.
© 2001 National Burglar & Fire Alarm Association
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Magnetic Reed Switch
Switch changes
with magnet away
from switch.
Magnet
Magnet
Contacts are enclosed In hermetically sealed tube.
© 2001 National Burglar & Fire Alarm Association
8-4
Mechanical Switches
• Simple & inexpensive.
• Easily defeated.
• Subject to corrosion.
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8-5
Door & Window Switch
False Alarms
• Doors & windows must be tight fitting &
locked.
• Door & window contacts must be free of paint
& varnish.
• Make sure there is no door or window
warping.
• Any broken contacts should be replaced
immediately.
© 2001 National Burglar & Fire Alarm Association
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Foil Patterns
18 ”
Plate Glass
Re-inforced or Sun Film Coated
Tempered Safety
Multi-pane
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Foil False Alarms
• Foil contains lead & needs to be
replaced every 3-5 years due to
extreme summer weather.
• It can be easily scratched or
damaged.
• Scratched or damaged foil can
cause false alarms.
© 2001 National Burglar & Fire Alarm Association
8-8
Shock or Vibration
Detectors
• Vibration causes contacts to open.
• Tension on contacts is adjustable.
• Contact opening may be too fast.
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8-9
Mercury Devices
Closed
Open
• Vibration of mercury sealed in
tube causes an alarm.
• Sensitivity adjusted by varying
tube angle.
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Piezo Electric Devices
• Small crystal vibrates to
produce electricity
when glass is broken
• Can be self contained
or be wired to a
processor.
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8-11
Shock Sensors
Impact
At Rest
• Use simple sensors connected to
processors that decide when to initiate
an alarm.
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Screens
• Screen is laced with
thin wire.
• Alarm circuit is run
through the wiring.
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8-13
Interior Sensors
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Combination Motion Sensors
Ultrasonic Detectors
Microwave Detectors
Passive Infrared Detectors
Photoelectric Detectors
Audio Processors
© 2001 National Burglar & Fire Alarm Association
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Motion or Space
Detection
What changes occur when people move?
The detector must respond!
© 2001 National Burglar & Fire Alarm Association
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Avoid False Alarms!!
• What changes occur when there are no
people present or moving?
• Detector must NOT respond!
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8-16
Disguised Sensors
Various types of sensors can be
concealed or disguised as:
1. Duplex Electrical Outlets.
2. Thermostats.
3. Speaker Grills.
4. Smoke Detectors.
5. Light Fixtures.
© 2001 National Burglar & Fire Alarm Association
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Motion Sensor Uses
Trap
Spot
Channel
Volumetric
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Older Motion Sensors
• Ultrasonic
• Listens to reflected sound, & responds to a
change from movement.
• Microwave
• Monitors for a reduction in level of transmitted
energy which may be caused by motion.
• Photoelectric
• Responds to an interruption the light beam sent
between a transmitter & receiver.
© 2001 National Burglar & Fire Alarm Association
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Passive Infrared
Responds to
changes of
infrared energy levels
within specific
fields of view.
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Poor or No Catch
Motion
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0
Gradual
Change
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Good Catch
Motion
+
0
Rapid Change
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PIR Patterns Pet Alley
Think! Pets climb, jump, & go places they shouldn’t.
If a pet can cause a false alarm assume it will.
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Dual Technology
Sensors
Microwave
PIR
Overlapping patterns of the two
technologies provide stability preventing
false alarms
in harsh environments.
© 2001 National Burglar & Fire Alarm Association
8-24
What Can Cause Motion
Detector False Alarms?
– helium balloons (especially mylar)
– pets
– bugs on the lens
– curtains
All interior equipment should be dusted,
vacuumed around, etc for bugs &
spiders.
© 2001 National Burglar & Fire Alarm Association
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Glassbreak Sensors
Audio discriminators listen for
the sounds of forced entry;
–Glass Breakage
–Splintering Wood
–Etc.
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Glass Break Sensor
False Alarm Sources
• Single technology glass break sensors
can mistake the following for glass
breaking:
– Clinking glasses
– Strong or heavy vibrations
– Pots & pans hitting each other
– Other sounds similar to the sound of glass
breaking
• USE DUAL TECHNOLOGY SENSORS!
© 2001 National Burglar & Fire Alarm Association
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Pressure Mats
Pressure on the mat
shorts the metal strips
together.
Mounted under carpet in area
likely to be walked upon.
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Stress Sensors
Mount under
joists in area
to be covered.
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Mats & Stress Sensor
False Alarm Sources
Both are stable until
furniture is rearranged
around or on top of them
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Manual Devices
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Foot rail.
Holdup button.
Money clip.
Portable duress sensor.
Touchpad Activated
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Manual Devices
False Alarm Sources
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Improper user training
”Single action" buttons
“Single action” money clips
Batteries in wireless buttons that are not
replaced when the manufacturer
recommends.
© 2001 National Burglar & Fire Alarm Association
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Fire Alarm Sensors
• Smoke Detectors.
• Heat Detectors.
• Flame Detectors.
• Manual Pull Stations.
© 2001 National Burglar & Fire Alarm Association
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Condition Monitoring
• Alarms Can Be Used to Monitor:
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Medical Emergencies.
Low or High Temperature.
Failure of Equipment.
Operation of Equipment.
• (Generators, Sump Pumps , Etc..)
– Water or Moisture
– Power Failure
© 2001 National Burglar & Fire Alarm Association
8-34
Carbon Monoxide Gas
Alarms
• Indicates an unacceptable level of carbon
monoxide gas is present in a room.
• May indicate a failure in a furnace or
improper ventilation in a room with a fireplace
or wood stove.
• Even limited exposure to high levels of
carbon monoxide can be lethal to humans
and animals.
© 2001 National Burglar & Fire Alarm Association
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Alarms: The First
Line of Defense
1- Introduction
2- What is an Alarm System
3- What is A False Dispatch
4- Impact of False Dispatches
5- Causes of False Dispatches
6- Preventing False Dispatches
7- User Controls
8- Sensors
5 Minute
Break
10 Minute
Break
9- The Control
10- The Central Station
11- How Authorities Respond
12- What to expect for Alarm
Co.s
13- The Alarm Ordinance
14- Sources of Information
15- Site Survey
30 Minute
Lunch
60 Minute
Lunch
Next
Chapter
© 2001 National Burglar & Fire Alarm Association
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