Bob Dolph Bob.Dolph@bobit.com
February 2008
Just as every person tries to find their true compatibility match, security experts are faced with the daily challenge of finding the correct alarm sensor for a specific security application. The range of technology selections is vast and can include both old and/or new technology. Experienced integrators have learned that while the latest technologies are new and exciting, keeping the product application simple yet efficient can often lead to the best technology match. With the popular use of wide-area security sensors such as the ever popular passive infrared (PIR) detector, it is easy for the security expert to overlook the many niche application detectors that, when applied properly, can fill in those little gaps in their overall security model.
It is often easy to catch people walking through open areas, but how does one effectively protect property along the fringe areas, or detect those criminals who slink up and over walls and rooftops? How can one protect against the tampering of objects? How can those little leaks be tightened up in the security dam?
What follows is an examination of a large variety of security intrusion sensors. Some are new, some are old, and some you may not have even heard of before. The goal is to come away with a larger bag of tricks and techniques to help foil even the most devious of criminals.
Techniques Used to Protect High-Security Rooms and Vaults
What are some ways to detect intrusion at the perimeter of a room? Some of the obvious are magnetic proximity reed switch sensors/contacts for doors and windows, both standard and balanced for high security. Make sure to select the right type of contact for metal frames and plenty of air gap tolerance to reduce false alarms and achieve proper sensitivity.
There is a new type of magnetic contact on the market called the "Magnasphere." It uses a small conductive ball in a miniature spherical enclosure that, when influenced by a nearby magnet, creates a unique configuration that will keep even sophisticated criminals at bay.
One old technique that is still being used for protecting the penetration of walls and doors is the art of lacing. This can either be done with fine wire or foil strips. The fine conductors are installed in a grid configuration, allowing the barriers to have a lining. Any opening small enough for a person to fit through will be detected. UL security certification requires that an opening greater than 96 inches - with the smallest dimension not exceeding six inches - be detected. When the lacing surface is covered, there is no indication that this type of security has been applied to the barrier. This lacing technique is also used with specially designed window screens and doors for complete coverage of an opening.
For high-security rooms and vaults, another intrusion device is the seismic sensor. Devices such as the Bosch ISN-SM Series and the Honeywell UN3 come with microphones and digital signal processors (DSPs), and work well on concrete and steel reinforced vaults. However, if you are looking to provide cost-effective protection from drilling and tampering of metal equipment enclosures, then GE Security makes a nice little sensor, Model 5402 shock sensor. Another interesting method to inconspicuously detect the movement of personnel is the use of stress detectors, or as engineers call them, strain gauge detectors. This is a device that can detect the extra stress placed on a roof or floor support beam when a person walks on it.
Sure Action of Hampton Bays, N.Y., is one manufacturer that offers such a device. The company's, Pulsor sensor can be fastened to prepared supports and then analyze the pulses of people walking on the structure. Some other interesting areas of application might include steel fire escapes, under window sills and stairways, tractor trailer beds, marine craft decks and chain-link fence posts.
Object Removal Triggers Electrically-Supervised Alarm Circuit
A challenging area for alarm sensors is detecting the removal of valuable objects within an overall active, yet unprotected, area. This might include items such as office or construction equipment. To protect these items, a good sensor configuration is the GE Security 2100 Series "Magnapull" pull-apart cord. This device provides an electrically-supervised alarm circuit allowing equipment to move, but not to be removed without triggering an alarm.
A very good source for the security professional when reviewing various security intrusion sensor applications is the newly revised 192-page GE Security "Intrusion Sensors Application Handbook," which is now available as a free download to security professionals at www.gesecurity.com. This book is a must for a security practitioner's library.
Shock, Acoustic Sensors Discern Glass-Breaking Sound Waves
In olden days, window glass was mainly protected by applying thin strips of conductive foil that upon being broken would activate the alarm. However, today window glass is protected by a variety of specially designed shock sensors. These sensors mainly have two categories: sensor modules that mount directly to the glass or glass mounting frame, and acoustical glass-break detectors that "listen" for the sound signature of breaking glass.
The sound of breaking glass is very complex and consists mainly of two key parts: the normal higher frequency crashing sound we all hear, and a lower infrasonic sound shock wave that is created by the flexing of the glass when broken. Together, both sounds create a unique sound signature that is specific to the type of glass being broken, such as plate, laminated, film coated, reinforced (wire mesh) and tempered (safety).
While these types of sensors are very versatile, they need to be installed closely following the manufacturer's guidelines. There is always a fine line of distinction between configuring glass detectors for good detection and minimal false alarms.
One technical item learned very early on when installing acoustical glass-break detectors is that sound, barring some echoing, is very directional. The Honeywell FG 1025Z with "time of arrival" (TOA) signal processing of the glass-break sounds has two microphones, and due to the directional nature of sound, it can tell if the sound came from the expected window protection area or another nonalarm area. This is due to how the sound wave arrives at the microphones mounted on opposite sides of the sensor.
Ultrasonic, Microwave, PIR Sensors Guard 3-Dimensional Areas
The primary application intrusion sensors are designed to handle is detecting suspicious activity in three-dimensional environments. These security devices are often referred to as "volumetric" detectors. Through the years, three main volumetric detection technologies have prevailed: ultrasonic, microwave and PIR.
Ultrasonic - These intrusion sensors detect motion throughout an area using what is referred to as the doppler effect. These devices send out a high frequency sound wave that is just above the human hearing range. As these sound waves bounce around objects and walls in an area, they set up a signature pattern. When a person walks through the area, the sound wave pattern changes with the reflection off the moving person and is detected by the sensor's electronics.
Due to the development of newer technologies, ultrasonic-only motion sensors are almost nonexistent today; however, the technology is still used for building automation, mainly light control and automatic door openers. One of the main problems with this technology was adjusting and positioning these devices so that certain environmental conditions would not cause false alarms. However, the little-known upside to ultrasonic-only sensors is that they can completely fill an enclosed area with irregular boundaries, and depending on how well the sound patterns might fill that area, the devices could be used to detect the slightest movement.
Microwave - These motion detectors work similar to ultrasonic technology; however, the energy transmitted is at a considerably higher frequency and is sometimes referred to as "radar" technology for detecting movement. Again, once very popular, just a few microwave-only intrusion sensors can still be found now.
Positioning of these sensors must be carefully planned as they can detect through a building's walls and windows. It is best to position a microwave-only detector to look down at an area of detection. If not properly positioned, reflected energy from nearby personnel and vehicular traffic can trigger a false alarm. There is, however, an upside to using microwave-only detectors in high-security applications. Because the technology can detect movement through walls and ceilings, the device can be positioned in a stealth mode so that personnel cannot visually detect its presence. GE Security's SR-RCRxx Series can be optioned for mounting in the radar-only high-security stealth mode.
PIR - This is another very popular type of volumetric detector. This device is typically only passive and establishes a complete pattern of lookout and down sensors that can detect the heat differential from a human body walking at a certain rate through the detection fields. A PIR-only detector, as with other sensors, can have false alarm activations from problematic heat sources if not positioned properly. The device can also be susceptible to being compromised in high-security applications by physically covering the PIR elements.
One technique to reduce PIR false alarms is to establish an alarm circuit in which several PIR detectors need to be tripped simultaneously to be considered an actual alarm. This is sometime referred to as "cross-zoning" and is a standard feature in UL-Listed CP-01 alarm controls. Small objects such as rodents or insects might trip one PIR sensor but not both.
An interesting product that uses this application is the new BX-80NR outdoor PIR detector from Chino, Calif.-based Optex. This sensor uses dual beams to provide perimeter intrusion detection.
Combining Technologies Can Help Overcome False Alarm Issues
The most popular method of volumetric intrusion detection is using the combination of PIR and microwave technologies in one device. Since the environmental variables that could cause false alarms are different for both technologies, but are similar for detecting a true alarm, the combining or logically adding of intruder detection makes for a win-win situation.
Outside motion security is always a big challenge when faced with movement of small birds, animals and foliage. Protech of Sparks, Nev., has developed the Piramid sensor, which uses combinations of PIR and microwave to provide reliable detection around towers and ladders. This sensor is used for strategic area or specific asset protection, and is generally used as a "gap filler."
Additionally, the combined use of microwave and PIR technology allows for the detection of a PIR-compromising technique known as masking. The obvious masking technique for PIR detectors is covering the detection lens; however, this can be done in a stealth manner. When a high-security multitechnology motion detector is masked, the microwave can still detect through the compromised PIR technology, thereby allowing for an indication of professional tampering. Some PIR detectors also use active infrared technology to counter masking attempts.
Include Digital Video With Intrusion Sensors for Best Protection
The big buzz now in volumetric intrusion detection is video analytics. The digital video field-of-view (FOV) is the perfect scenario for detecting suspicious intrusion activity. Some current providers use a variety of intrusion technologies with complementing video.
A popular video/motion sensing device is the VIA-Pro intrusion alarm from RSI Videofied of Minneapolis. This sensor uses a combination of PIR detection with versatile wireless low-cost digital imaging for rapid alarm verification. This appears to be the direction future alarm intrusion sensing with verification is headed.
Recently, another version of volumetric intrusion technology hit the security market with some new and exciting applications. The technology is called Ultra Wide Band (UWB); the product is called UltraSensor, and it is from Ultravision of Salem, N.H.
UWB signals have been used in geophysical analysis systems for years. While microwave technology works on a single frequency, UWB works on a spectrum of frequencies that can detect motion and movement better through surfaces such as walls and roadways. It can also analyze direction and rate of intrusion movement. The technology has been used for some time to detect survivors buried under damaged buildings. Expect to see more security applications with UWB signals in the near future.
 Bob is currently a Security Sales & Integration 's "Tech Talk" columnist and a contributing technical writer. Bob installed his first DIY home intercom system at the age of 13, and formally started his technology career as a Navy communication electronics technician during the Vietnam War. He then attended the Milwaukee School of Engineering and went on to complete a Security Management program at Milwaukee Area Technical College. Since 1976, Bob has served in a variety of technical, training and project management positions with organizations such ADT, Rollins, National Guardian, Lockheed Martin, American Alarm Supply, Sonitrol and Ingersoll Rand. Early in his career, Bob started and operated his own alarm dealership. He has also served as treasurer of the Wisconsin Burglar and Fire Alarm Association and on Security Industry Association (SIA) standards committees. Bob also provides media and training consulting to the security industry. |