Shock Sensors Explained
Double-sided tape is used to attach shock sensors directly to the glass itself. The sensor consists of a transducer embedded in a normally closed circuit. Upon detection of shock, the transducer opens the circuit, sending a signal to the panel indicating that the zone is open.
There were times when the earliest shock sensors would false alarm whenever the window vibrated as a result of passing traffic or low-flying aircraft. However, newer shock sensors, which utilize transducers, are able to distinguish between the vibration pattern of shattering glass and other types of vibration. As a result, a shock wave that breaks the glass is required to activate the sensor. Shock sensors are designed to protect only a single pane of glass. When a window or door has more than one pane of glass, each pane must have its own shock sensor.
Unfortunately, it is not possible for shock sensors to detect cracks or bullet holes since they detect the shock wave accompanied by a pane of glass shattering. Despite the fact that this is difficult to do properly, a burglar will not trip a shock sensor if he uses a circular cutter to make a hole. Nevertheless, a properly installed alarm system combines exterior contacts like glass break detectors with interior sensors like motion detectors.
For shock sensors to work properly, they should be mounted in the corner of the window pane. An ideal distance from the edges of the window frame will be specified in the installation manual. This is usually one inch (2.4 cm) from the frame. It is common for manufacturers to specify a maximum thickness of 1/4″ (6.35mm) for the glass and a radius of 8′ (2.4m) to 10′ (3m) for the detection area.
The shock sensor should be tested by striking the glass opposite the corner on which it is mounted. It’s commonly recommended to use a plastic or blunt rubber object to test, for example the back of an insulated screwdriver. To test a shock sensor, it is necessary to hit the glass with a considerable amount of force, but still less force than is created when a window shatters.
Acoustic sensors consist of a microphone, a transducer, and an ASIC microprocessor that has been programmed to detect different types of glass breaking. Installers sometimes install an acoustic glass break sensor in a room with several windows to protect them all at once. Using the manufacturer’s placement instructions it is possible for the installers to place the sensor in a spot that keeps as many windows within its detection zone as possible.
Professional installers understand how sound travels and know key elements to keep in mind that when utilizing acoustic sensors. They need to be aware that the shape of the room and its materials will influence how fast the waves travel. Sensors can also interpret and define waves differently depending on the type of surfaces in a room. For instance, a room with numerous hard surfaces will interpret a sound differently than one with soft surfaces. The reason being that waves will be reflected off of the hard surfaces and soft surfaces will absorb the sound.
Typically a sensor’s sensitivity can be adjusted. In an area with sound reflecting surfaces it’s best to turn down the sensitivity level. While increasing it in an area with sound absorbing surfaces to decrease the chance of false alarms. Wood paneling, tile floors, and melamine-covered furniture all reflect sound while carpets, drapes, and wall hangings absorb it. Another example is a bookshelf filled with books. The shelves commonly reflect sound, while the books typically absorb sound. It’s possible for some acoustic sensors to include adaptive microprocessors. In cases where false alarms are common with glass break sensors, changing the sensor to one that has adaptive technology, or another that has a different noise profile, may prevent future false alarms.
It is possible to purchase glass break simulators from some manufacturers, which play the sound of breaking glass. Glass break simulators are used to temporarily mount an acoustic glass break detector using a 9-volt battery and determine the best placement and sensitivity level using an acoustic glass break detector. A sensor’s noise profile differs depending on the manufacturer, so it is important to test it with a simulator made by the same manufacturer.
It is easy for acoustic glass break detectors to misinterpret normal sound reflected by materials such as ceramic tiles, marble, and architectural glass. It is for that reason that detectors with lower sensitivity should be used in rooms with hard surfaces.
Avoiding False Alarms
Acoustic glass breaks listen for this unique sound signature created when glass shatters. This is best described as a dull thud and a high pitched sound simultaneously. Glass break detectors may misinterpret items that produce multilayered sounds when dropped. It is notorious that keys dropped onto a table trigger the sensor of a glass break.
While the alarm is armed, subscribers should be instructed not to throw keys, toolboxes, hobby supplies, or similar sounding objects in the glass break’s zone of detection.
Acoustic glass break detectors should be installed with caution in playrooms, especially those without carpets. When children throw balls, rattle toy boxes, and act generally like children, they often inadvertently set off false alarms. By using a battery powered glass break detector and a glass break simulator, an installer can carefully place the detector so that an area not monitored exists near the floor. In the absence of such a location shock sensors would be more appropriate.
It is not recommended to use acoustic sensors in humid locations, such as bathrooms. The microphone inside these sensors contains a paper element and can be easily affected. It is common for kitchen surfaces to be made of metal, tile, stone, or other hard materials. As a result, it is possible to set off acoustic glass break detectors with typical kitchen use. For example, this can be done by washing the dishes, cutting vegetables with knives, or clattering utensils. Glass break simulators can be used to determine a practical spot for mounting a detector. Acoustic sensors can also malfunction due to humidity from sinks and dishwashers.
It’s also important to know that the most common type of acoustic sensor cannot penetrate drawn drapes. For this reason, the sensor should be flush mounted. And always set to medium or low sensitivity between the window and the glass, facing downward, if possible.
If you are looking to update security features for your business, like adding Glass Sensors let RC Security help. Our continued research and partnerships with premium brands allow us to offer better quality every time.
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RC Security Consulting protects the heart of Texas with design, installation, retrofit, repair, inspection, and monitoring of commercial security systems. We are centrally located in Collin County and provide service for almost 200 miles in all directions. Connect with us on LinkedIn to learn more.