The design of commercial and industrial systems is very similar to residential systems, except that heavier-duty equipment is normally used. And, the require- ments for these structures are somewhat different from residential demands. This chapter covers the basic techniques necessary to design and calculate the material requirements for typical commercial and industrial occupancies.
The floor plan of a small commercial building is shown in Fig. 8.1. A burglar- alarm panel and a telephone dialer (Fig. 8.2) are located in the storage area. The relay-type control panel has one protective circuit, output for 6-V dc alarm-sending devices, and a silent holdup alarm with telephone dialer to call emergency numbers and deliver voice messages.
Glass on the front door is protected with window foil connected to foil blocks that are then connected to the protective circuit wiring in the alarm system. Door cords are used to provide a flexible connection from the foil blocks on the door and window to a solid contact point adjacent to the door (Fig. 8.3). Flexible door cords also can be used on moving windows and money clips can be installed in cash drawers.
The large display window is again protected with foil connected to foil blocks, and the office area is protected by an ultrasonic motion detector (Fig. 8.4). A surface-mounted door contact (Fig. 8.5) is used to protect the rear door of the building. Legal entry is permitted by use of a key lock.
Security Equipment for Commercial Applications
Magnetic contacts are used on doors and windows in closed-protective circuits, in direct-wire systems, and also in open-circuit applications. Movable elements with- in the protective switch unit of the magnetic contacts usually consist of a single flexible contact arm that provides a solid metal circuit path from the terminal
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screw to the end of the contact point. The circuit continuity should not depend upon conduction across a hinge joint or through a coil spring.
When magnetic contacts are mounted on either noncoplanar or ferromag- netic surfaces, magnet and/or switch units should be held away from their respective mounting surfaces to:
■ Bring switch and magnet into close proximity when the door, window, etc., is closed.
■ Reduce the shunting effect of ferromagnetic materials so that positive switch pull-in occurs when the magnet approaches to within 1Ⲑ
4″ of the
switch.
Mechanical contacts are used as emergency, panic, or fire-test switches. Ball contacts and plunger contacts (Fig. 8.6) are used in both closed- and open-cir- cuit applications.
Figure 8.1 Floor plan of a small commercial building.
Figure 8.2 Relay-type control panel utilizing one protective circuit and having output for alarm-sounding devices and other detection/alarm capabilities.
Figure 8.3 Glass door with security devices installed.
Figure 8.4 Ultrasonic motion detector.
Mercury contacts are sometimes used in low-energy alarm or signal systems to detect the tilting of horizontally hinged coverings: windows, doors, and access panels. At horizontal openings it is best to install mercury contacts that can be adjusted for sensitivity after installation.
For combined detection of either opening or breakthrough, cord-mounted contacts with foil connected to takeoff terminals should be used. Wiring dia- grams of mercury contact connections are shown in Fig. 8.7.
Holdup switches are usually installed under counters or desks in banks or stores, where an employee observing a holdup might be able to signal for help. In banks and other places where large amounts of money are exchanged, a money-clip alarm device is sometimes used. They automatically trigger an alarm when all bills are removed from a cash drawer. A bill inserted in the clip holds its switch in the normal position. Additional bills on top of the clip keep it concealed. Bills can be added or removed as required for normal business operations so long as one remains in the clip. However, the removal of all bills trips the clip switch to signal an alarm.
Money-clip alarm devices should be installed in the largest bill compart- ment of cash drawers and connected to the building alarm system by means of a retractable door cord. If exceptionally busy working conditions create the possibility of a false alarm because the bill in the clip might be accidentally removed, two money clips should be used at each station and wired so that both must be emptied to cause an alarm.
Window foil is used extensively in commercial applications. For fixed win- dows, the connections to the building alarm system are usually made through foil blocks. For movable windows and doors, a retractable door cord must be used, or plunger contacts can be installed (Fig. 8.8).
Ultrasonic motion detectors for commercial applications are essentially the same as those described for residential use. However, the range of detection is sometimes extended on the units designed for commercial use. For example, a typical coverage pattern of a motion detector is shown in Fig. 8.9. Notice the coverage here is 15 feet wide by 30 feet deep.
Figure 8.6 Cross-sectional view of plunger contacts.
Commercial telephone dialers are available that dial emergency numbers and deliver voice messages. Most distinguish between burglar and fire-alarm channels. A typical wiring diagram is shown in Fig. 8.10.
Digital alarm transmitters
Digital alarm transmitters are relatively popular in large commercial estab- lishments. They can be programmed on computer chips to meet the exact requirements of any business. In a typical model, each line corresponding to
Figure 8.7 Wiring diagram of mercury contact connections.
an alarm code is limited to13 characters. A blank space between two words on the same line will take up one character.
These units are specifically designed for central-station monitoring of com- mercial buildings. The unit consists of a transmitter, a special module, and a subscriber control station.
One type of module has three input zones:
■ Zone A: Two-wire, closed-circuit input generally used for a foil circuit. This zone can be 24-hour or key-controlled by the subscriber control station.
Figure 8.8 Location of plunger contacts in movable window.
Figure 8.10
W
iring diagram of a commercial telephone dialer
■ Zone B: Three-wire, closed-circuit and open-circuit input for perimeter doors and windows. This zone is armed and disarmed by the subscriber control station. It can be connected to the detector contacts so that an open or a crossed circuit will produce an alarm.
■ Zone C: Three-wire, closed circuit and open-circuit input for internal protec- tion devices, such as ultrasonic motion detectors, infrared beams and pas- sive infrared detectors. They can be wired so that either an open or a crossed circuit will produce an alarm.
Six output leads are provided from the module to trip the control: 1. Zone A open
2. Zone B open or crossed 3. Zone C open or crossed 4. System armed (closed—night) 5. System disarmed (open—day) 6. Alarm circuit restored
Zones A and B can be connected to the same channel of the transmitter, thereby using only five channels for the module. If this is done, a daytime foil break will be reported as “perimeter alarm—day.” The sixth channel may then be used for 24-hour reporting of fire alarm, holdup alarm, or equipment super- visory monitoring. A holdup alarm can also be connected to the same channel of the transmitter as Zone C. If this is done, a holdup would be indicated as “interior alarm—day.”
When the subscriber leaves, an interior alarm and the perimeter door cir- cuit will both be tripped and they will be reported. A restore signal will be reported only when all three zones have returned to normal.
The subscriber control station consists of a key switch and two LEDs mount- ed in a stainless steel plate. One LED indicates that all three zones are good. When the subscriber turns the key to arm the system, the second LED comes on, indicating that the transmitter is reporting the closing signal. This LED goes out when the signal is received at the central station.
Because the transmitter can report multiple signals on the same call, it is prac- tical to locate the subscriber control station near the exit door. Consequently, if the subscriber arms the system and leaves immediately, the interior alarm, perimeter alarm, and restore signal will all be transmitted on a single call. This will take about 30 seconds, including dialing time. The receiver at the central sta- tion will be tied up for about 15 seconds after it answers the call.
Surveillance cameras are being used extensively in banks and stores to pre- vent holdups, pilferage, and burglaries. Because thieves are notoriously cam- era-shy, the presence of a surveillance camera is often sufficient to make a would-be robber change his or her mind. If a business should be robbed, a sur- veillance camera provides strong evidence to aid police and courts.
Most surveillance cameras can be adjusted to take individual still pictures at preset intervals to keep a continuous eye on the premises. The Super 8 Kodak surveillance camera, for example, provides continual recorded surveil- lance for up to 180 hours with each 100-foot roll of film. There are up to 7200 individual photographs to assist in positive identification and apprehension. This unit can be activated by a switch on the camera, by remote control, or automatically by relay from the external alarm system.
Video tapes have been substituted for film in recent years, but the principle is basically the same.
Miscellaneous security equipment
Vibration detectors are often used on buildings to detect vibrations caused by forced entry. Such detectors have been used on a variety of construction mate- rials, such as hollow tile, plaster and lath, brick, concrete, metal ceilings, wood, and concrete block with brick veneer. Once mounted, they can be adjusted with a set screw for the desired sensitivity.
Some establishments maintain a security fence equipped with fence-guard detectors. This type of detector will detect climbing, cutting, or any other pen- etration of the fenced area. Most of these detectors operate on standard closed- circuit controls.
Fence-guard detectors use a vertical-motion detector that is sensitive to movement created by climbing or cutting the fence. Normal side motions such as wind or accidental bumping do not affect the detector and cause false alarms. They are normally mounted about midway up the fence, and at every 10-foot length of fence. Most of these devices set off the alarm if they are tam- pered with or if the wire is cut. They may be connected to a control panel and the alarm will “sound” in the form of a bell or horn, or it will silently dial the local law-enforcement agency.
Outdoor microwave detectors are used to protect large outdoor areas, such as parking lots, construction sites, and building perimeters. In operation, a solid circular beam of microwave energy extends from a transmitter to the receiver over a range of up to 1500 feet. Any movement inside of this beam (Fig. 8.11) will activate the alarm.
Thermistor Sensors
The continuous, linear, thermal sensor is a small-diameter coaxial wire that is capable of sensing temperature changes along its entire length. The sensor is made up of a center conductor and an outer stainless steel sheath. The center conductor is electrically insulated from the outer sheath by a ceramic thermistor material.
The term thermistor is derived from the words “thermal resistor.” Thermistors are actually thermally sensitive semiconductor devices and con- sist of two basic types:
■ NTC (negative temperature coefficient)