Alarm and Sensor Technologies: Difference between revisions

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===Overview of Alarm Technologies===
===Overview of Alarm Technologies===
[[File:Deter horiz.png|600px]]
<BR>
The point of physical security measures is to provide a complete triangle of <B>Deterrence</B>, <B>Detection</B>, and <B>Delay</B>, ultimately leading to <B>Response</B> from the site personnel, police, etc.
The point of physical security measures is to provide a complete triangle of <B>Deterrence</B>, <B>Detection</B>, and <B>Delay</B>, ultimately leading to <B>Response</B> from the site personnel, police, etc.
<BR>
<BR>
Alarm circuits and sensors are the "detection" portion of this cycle. The typical alarm system includes overlapping sensors to check for door/open closed status, glass breakage, motion, and more. These sensors are electrically "supervised" by a microcontroller and monitored constantly for changes in state.
====A basic alarm circuit====
Commercial alarm systems are typically wired up as follows:
*One or more sensors are placed in series to form a "loop." Each loop forms a sensor zone.
*Sensor zones are always wired up as "normally closed"
*Each zone includes a resistor in the middle of each loop, a resistor at the end of each sensor loop, and the ability to check voltage or resistance at the alarm panel. circuits.
<BR>
<BR>
Alarm technology exists to augment humans in meeting these goals. The typical alarm system includes overlapping sensors to check for door/open closed status, glass breakage, motion, and more. These sensors are electrically "supervised" by a microcontroller and monitored constantly for changes in state. Multiple sensors may be placed in series to form a "loop."
[[File:3-state_alarm_wiring.png|600px]]
<BR>
<BR>
A proper implementation will include a series resistor somewhere in the middle of each loop, a resistor at the end of each sensor loop, and the ability to check voltage or resistance at the alarm panel. Sensor zones are always wired up as "normally closed" circuits.
<BR>
<BR>
This allows up to 4 states to be identified:
*Sensor activated (i.e. door opened or motion detector sensing motion)
*Sensor not activated (i.e. door closed)
*Open Circuit (i.e. wiring fault or cut)
*Shorted Circuit (i.e. deliberate shorting or bypass of a sensor)
 


====Sensors====
====Sensors====

Latest revision as of 10:35, 14 May 2012

Overview of Alarm Technologies

Deter horiz.png
The point of physical security measures is to provide a complete triangle of Deterrence, Detection, and Delay, ultimately leading to Response from the site personnel, police, etc.

Alarm circuits and sensors are the "detection" portion of this cycle. The typical alarm system includes overlapping sensors to check for door/open closed status, glass breakage, motion, and more. These sensors are electrically "supervised" by a microcontroller and monitored constantly for changes in state.

A basic alarm circuit

Commercial alarm systems are typically wired up as follows:

  • One or more sensors are placed in series to form a "loop." Each loop forms a sensor zone.
  • Sensor zones are always wired up as "normally closed"
  • Each zone includes a resistor in the middle of each loop, a resistor at the end of each sensor loop, and the ability to check voltage or resistance at the alarm panel. circuits.


3-state alarm wiring.png

Sensors

  • Passive Infrared (PIR)

This type of sensor is used to protect inside and outside spaces by watching for changes in radiated IR.

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