Early alarm systems used a normally-closed loop and a battery and bell. The two types of alarm systems available now are the local alarm and the reporting alarm system. A hard-wired sys-tem will use wires to connect the various switches or sensors in the system. A wireless system will use a series of transmitters and a receiver to eliminate the need for wiring. A combination system will use both wired and wireless switches and sensors.
An end-of-line resistor, EOLR, is used to set a certain loop cur-rent. If this current rises or drops, the alarm system will trig-ger. A resistor’s value can be determined by measuring it with a VOM or by decoding the resistor’s color bands. A system can be expanded by using a polling loop and remote-point modules.
Wireless systems use UHF transmitters and a receiver.
The Americans with Disabilities Act (ADA) specifies the placement of pull boxes and output levels of visible and audible signal appliances in an alarm system. Local codes,
particularly fire codes, may also require specific types of installations.
A complete alarm system is made up of a main control panel, input devices wired to loops or to transmitters, a power sup-ply, and output devices. Bells, horns, sirens, and speakers are used as output or signaling devices. Another output de-vice—the digital communicator—can be used to contact a central reporting agency, police, or fire department, if the alarm system is tripped. Perimeter detectors are used to protect the windows and doors of a building. Perimeter detectors include magnetic contacts, foil, plunger and roller switches, vibration switches, and glass-break sensors. Interior detectors can include ultrasonic, microwave, photoelectric, passive infrared or PIR, and dual-technology sensors. A key-pad is used for data input, code number input, and to view system conditions on an LED or LCD screen.
Modern alarm systems have many functions and features that are easily used to simplify arming and disarming or to bypass certain zones. An alarm system’s main control panel is normally mounted in the basement of a residence or in the basement or first floor closet of a business. An alarm system will connect to an electric outlet, to the service entrance ground rod, and to the telephone service. Doors and windows can be protected by surface-mount or concealed magnetic contacts.
PIRs can be mounted in a corner of a room using a standard mounting bracket. Some ultrasonic and microwave sensors have a flat case that can be mounted to a wall.
The programming of a system is made easier through the use of a worksheet. The worksheet helps you and the customer choose all the codes, phone numbers, and other numbers needed to program the system.
Auxiliary security equipment includes closed-circuit cam-eras, lighting, labels and stickers, two-way mirrors, and dummy cameras. These may be necessary to prevent or de-tect shoplifting or vandalism. Obviously visible equipment, whether functioning or dummy models, deter burglary, vandalism, and shoplifting just by being on display.
Customers will normally contact you due to a recent break-in or a series of burglaries in a neighborhood. Making a careful survey of the home or business is the first step to designing a system for a customer. Besides testing equipment in your own home, attending trade association meetings will be an excellent way to learn about all the types of equipment available.
Do You Know Now . . .
What is an EOLR?
An EOLR is an end-of-line resistor used in a supervised loop of a fire or burglar alarm system.
What is a dual-technology sensor?
A dual-technology sensor will use a PIR in combination with an ultrasonic or micro-wave detector. In this case, both sensors must be triggered to produce an alarm output.
What is a panic circuit?
A panic circuit for a home normally uses a push button to sound the alarm in the event of an emergency. This push button is mounted in a bedroom or bath. In a business, the panic circuit may be used as a holdup circuit, calling police by means of a hidden switch or sensor.
NOTES
1
1. The EOLR is used to set the loop current that’s sensed by the alarm control panel.
2. An RPM is used in large systems to limit the wire runs from the main control panel.
3. Yes, a protective loop can contain both normally-open and
normally-closed switches and sensors.
2
1. An alarm bell uses a dome and a hammer. It will produce about 80 dBa. An alarm horn can produce more than one tone in a directional pattern. A horn will produce a sound at about 100 dBa. A speaker can produce many tones generated by an internal or external speaker driver circuit.
2. The automatic dialer or communi-cator will disconnect the call and make its own call. (This is called line seizure.)
3. Foil is difficult to install and is sub-ject to damage.
4. An ionization-type smoke alarm has an ionization chamber in which a small amount of radioac-tive material ionizes air. If smoke enters, it unbalances the electric charge on the ionized air, trigger-ing the alarm on the sensitive electronic monitoring circuit.
3
1. A panic circuit contains a push-button switch that’s normally in-stalled in a master bedroom to trigger an alarm if the switch is pressed.
2. A fire alarm circuit is always armed and is a 24-hour circuit.
3. A duress code is entered into the alarm system if someone is forcing the owner to disarm the system.
This code will normally trigger a silent alarm to the automatic dialer.
4
1. Yes. All fire-protection loops on all alarm systems provide 24-hour protection.