Glass break detectors ensure effective perimeter protection

November 2001 Perimeter Security, Alarms & Intruder Detection

Perimeter protection primarily concerns itself with the protection of all the access points of the perimeter of a building, such as doors, windows and roof. One such type of protection is the glass break detector like Rokonet’s Vitron, which is relatively false alarm-free and easy to install. A definite advantage of the glass break detector is its ability to protect an entire wall or room, resulting in less wiring for the installer.

Vitron can detect the crash of any glass type and thickness, while ignoring the breakage of nonframed glass or other possible sources of false alarms (eg keys jingling, telephone ringing, the hum of an airconditioner, whistling). When used in conjunction with reliable passive infrared detectors for internal space protection, it provides an important and viable form of protection for people and property.

The Vitron has a unique tester whereby audible sounds transmitted from the tester places the Vitron into a test mode. This eliminates the bother of opening and adjusting the Vitron for testing purposes, resulting in easier installation. This sophisticated tester has three different output levels for testing the full range of existing glass types - plate, tempered, laminated and wired.

Vitron glass break detector
Vitron glass break detector

Pre-programmed microphone calibration

The most important component in an audio glass break detector is the microphone. Unfortunately the sensitivity tolerance of microphones is greater than that of the other components in the circuit. The variation of voltage output for a given sound level may be as +40 and -30% for a good quality microphone.

Some manufacturers incorporate a potentiometer on the detector circuit board to adjust sensitivity. However, this can result in an installer adjusting the sensitivity to lower than the required level, thus reducing the catch performance of the device. With Vitron, this cannot happen. Because of individually computer-programmed sensitivity correction, Vitron has no user controls which may compromise performance.

Vitron tester
Vitron tester

Dead microphone supervision

Because of the importance of the microphone in any glass break detector, it is important that it is continuously supervised. To enable this, two levels of microphone testing are employed.

* Active testing: Whereby any environmental sounds within the protection range are picked up by the microphone and result in the flickering of Vitron's LED. This does not activate the relay.

* Passive testing: If the unit does not hear any sounds within a 24 h period, the LED will turn on and remain on until a loud noise is detected in the protection area. Failure of the LED to turn off indicates failure of the microphone.

Momentary latch facility

This feature allows for the installation of more than one Vitron on a 24 h zone. When detection takes place, the unit's LED will latch and stay on permanently until reset (in order to indicate which Vitron on the circuit was activated).

Ceiling-mount feature

The use of Vitron's new ceiling-mount bracket allows for easy installation and the correct alignment of the unit for maximum detection.

Test stations

A special feature of the Vitron test station is its programmed compensation of microphone sensitivity. The final test for the device goes further than just measuring parameters and comparing them with limits. It also corrects the output variations of the microphone and amplifier circuits by measuring the audio response of each individual detector and inserting a correction parameter into the nonvolatile memory of the unit's microcontroller.

To achieve uniformity of operation and to avoid using a potentiometer, the test fixture checks microphone sensitivity by applying calibrated sounds from its internal loudspeaker. Then the microcontroller programs are set according to the individual microphone response.

The Vitron range includes:

* Range for the detection of plate glass: 9 m (within line of sight).

* Range for the detection of all other glass types: 6 m (within line of sight).

For more information contact Sesco Security on tel: (031) 303 4022, e-mail: sales@sesco.co.za





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