Premises security (part 6) Non-video Surveillance
Non-video surveillance
Before moving on to Power Security for Surveillance Systems, I want to spend some time looking at what non-video security sensors are commonly used, how they function, how they are connected and their primary purposes.
Just to re-iterate, this blog is NOT intended to be a comprehensive in-depth technical exposé but rather an attempt to raise awareness of commonly available technology and hopefully to stimulate some comments or discussion around some of the devices / topics.
So ... Feel free to jump in with (topical) comments at any time. :)
So today, lets start with the most basic of security detection, the "closed loop"
On most security systems there is the ability to monitor an electrical circuit to ensure it remains continuously joined(closed) at all times. This means that devices(sensors) can be connected into that circuit in such a way that when the sensor is triggered, it "opens" the circuit, thus triggering an alarm.
And so to the first of the sensors, the NC or N/C switch.
NC or N/C stands for Normally Closed which means that when it is triggered it "opens" or breaks the circuit of which it is a part.
There are more varieties of 'switches' than you can imagine!
Just a few that spring readily to mind are;
The micro-switch, toggle switches, push-buttons, sliders, rotary, reed, pressure, thermatic, and the list can go on!
I'll just outline several of those more commonly used in security.
Description: Micro-switch
Operation: Pressure on spring-arm holds switch in "closed" state
Common Use: Tamper covers, doors, security grilles etc
Connectivity: 'common' and 'NC' contacts wired in series with monitored "closed circuit" loop.
Description: Magnetic Reed
Operation: Contacts held in NC state when in close proximity to a steady magnetic field (eg. Small bar magnet)
Common Use: Door and window security
Connectivity: Wired in series with monitored "closed circuit" loop.
Description: Thermatic
Operation: Contacts open / close in response to pre-determined temperature threshold.
Common Use: As simple fire detection sensors
Connectivity: In cheaper fire alerts these sensors are wired in their N/O state such that high temperature closes their contacts to activate an audible alert.
In monitored installation these switches are mostly used in their N/C state to ensure that the circuits back to the control panel are constantly monitored.
Description: Pressure-mat
Operation: Two foil surfaces separated by a thin layer of foam rubber with holes to allow contact between the two layers of foil when a weight is placed on the pad.
Common Use: Under carpets / rugs in main traffic routes to detect passage of intruders
Connectivity: Wired to a N/O monitored circuit to detect when the circuit is closed.
The next group is also effectively switches but they have additional electronics wrapped around them.
Before moving on to Power Security for Surveillance Systems, I want to spend some time looking at what non-video security sensors are commonly used, how they function, how they are connected and their primary purposes.
Just to re-iterate, this blog is NOT intended to be a comprehensive in-depth technical exposé but rather an attempt to raise awareness of commonly available technology and hopefully to stimulate some comments or discussion around some of the devices / topics.
So ... Feel free to jump in with (topical) comments at any time. :)
So today, lets start with the most basic of security detection, the "closed loop"
On most security systems there is the ability to monitor an electrical circuit to ensure it remains continuously joined(closed) at all times. This means that devices(sensors) can be connected into that circuit in such a way that when the sensor is triggered, it "opens" the circuit, thus triggering an alarm.
And so to the first of the sensors, the NC or N/C switch.
NC or N/C stands for Normally Closed which means that when it is triggered it "opens" or breaks the circuit of which it is a part.
There are more varieties of 'switches' than you can imagine!
Just a few that spring readily to mind are;
The micro-switch, toggle switches, push-buttons, sliders, rotary, reed, pressure, thermatic, and the list can go on!
I'll just outline several of those more commonly used in security.
Description: Micro-switch
Operation: Pressure on spring-arm holds switch in "closed" state
Common Use: Tamper covers, doors, security grilles etc
Connectivity: 'common' and 'NC' contacts wired in series with monitored "closed circuit" loop.
Description: Magnetic Reed
Operation: Contacts held in NC state when in close proximity to a steady magnetic field (eg. Small bar magnet)Common Use: Door and window security
Connectivity: Wired in series with monitored "closed circuit" loop.
Description: Thermatic
Operation: Contacts open / close in response to pre-determined temperature threshold.
Common Use: As simple fire detection sensors
Connectivity: In cheaper fire alerts these sensors are wired in their N/O state such that high temperature closes their contacts to activate an audible alert.
In monitored installation these switches are mostly used in their N/C state to ensure that the circuits back to the control panel are constantly monitored.
Description: Pressure-mat
Operation: Two foil surfaces separated by a thin layer of foam rubber with holes to allow contact between the two layers of foil when a weight is placed on the pad.
Common Use: Under carpets / rugs in main traffic routes to detect passage of intruders
Connectivity: Wired to a N/O monitored circuit to detect when the circuit is closed.
The next group is also effectively switches but they have additional electronics wrapped around them.
posted by Col. Sanders | 7:46 AM
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