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Home Security System | Wired and Wireless Alarm System
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Home Security Alarm Systems: Wired and Wireless Alarm System
There are a number of different
types of alarm systems. Some are hard wired alarm system, with wires
running from switches to a central location where a relay is energized or
de-energized to cause an alarm to be sounded. However, other type of alarm
system is called wireless alarm system with less wiring. They rely on
electronics for sensing and sending signals to central units.
They may be digitized, with programmed
codes that disable the system temporarily to allow entry into the premises and
to allow zone changes from time to time.
A Typical Hard Wired Alarm System
In a typical hard wired alarm
system, fire and security systems are wired together. Figure in below shows the
wiring diagram of a house with such a system. A detailed diagram of the wiring
for the security or fire system is given in next. Notice the closed loop
intruder detection circuit and how the switches work. Then examine the fire
detection circuit and how it is wired into the alarm system. Except for
the 120-volt line to the power supply, the rest of the wiring is low voltage.
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A typical hard wired alarm system |
The control unit should be
mounted between studs in a location with easy access from all rooms in the
house. This is usually in a hallway. The control box should be mounted out of
the reach of small children and not readily accessible to casual visitors.
When possible, the control unit,
the smoke or heat detectors and the auxiliary power or battery charger
(if used) should be connected to an individually fused 120-volt, 60-hertz
power source, according to local code requirement.
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Wiring
for a typical security or fire system
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Parts of The Hard Wired Alarm System
Different hard wired alarm systems
are available with various components in addition to the usual smoke or heat
and security parts. The choice of which parts and system to use depends on
1. Purpose of the system
2. Type of building it is in
3. Location
4. Other factors
A discussion of the common parts
in a typical hard wired alarm system follows.
Motion Detectors
A motion detector operates on
ultrasonic frequencies. An ultrasonic frequency is above the human hearing range.
The receiver transducer and transmitter are approximately the size of a
quarter. Any motion within the range of the unit causes a slight change in
frequency that is reflected back to the receiving unit. This difference in
frequency causes a relay or a transistor circuit to energize and complete the
circuit to the alarm control center. Ultrasound motion detectors are
quite sensitive. They can be activated by the movements of a dog or cat or even
by a hot air furnace causing curtains to move. These units need little or no maintenance
if wired into a household circuit.
Heat or Smoke Detectors
Heat detectors sense heat above
a certain temperature usually 136°F and activate an alarm system. Most heat
detectors contain bimetallic switches that remain open below a temperature of
135°F but close above that temperature, triggering an alarm. Some are activated
by higher temperatures of 200°F and the switches should be used in areas with
higher than normal temperatures, such as boiler rooms and attics. With most
smoke detectors, a concentration of less than 4% smoke in the air will sound
the alarm. What is 4%? Examine a cigarette smoking in an ashtray.
The plume of smoke rises, coils,
and spreads. It diffuses into the air. Somewhere above the cigarette is a region
where the smoke is drawn out and wispy, but barely visible. That concentration
is close to 4%. If that amount of smoke were concentrated in the chamber of a
smoke detector, it would set off the alarm. However, under normal conditions,
even a roomful of people smoking won’t trigger an alarm because smoke spreads
out so that the concentration is very low. Figure shows how the detector is
wired to the alarm system.
There are two types of smoke
detectors. In the photoelectric smoke detector, the smoke is
detected as it interrupts a small light from a bulb inside the unit. This type
is best at detecting thick smoke because that kind of smoke causes the light
beam to be interrupted.
This type of detector is used
primarily in the home, since house fires are usually of the smoldering type
with thick smoke. Less dense smoke triggers the radioactive detector. This type
of detector contains a dime-sized capsule of the radioactive element americium.
Smoke interrupts the beam of ions produced by the low-level radiation and thus
triggers the alarm. This type is best for detecting the kind of smoke generated
in business or commercial fires. It however, is more susceptible to false
alarms than the photoelectric type.
For maximum protection, heat
or smoke detectors should be placed in every enclosed area, including
bathrooms and closets. If any single dimension of a room exceeds 20 feet,
additional detectors should be installed. For unfinished attic spaces with gable
roofs, detectors should be installed 10 feet from the end and 20 feet apart on the
bottom of the ridgepole. Heat detectors should be installed on the ceiling but,
when necessary, may be mounted on a sidewall. When installed on a smooth ceiling,
each detector will protect a 20-square foot area. When installed on a wall,
detectors should be at least 6 inches and no more than 12 inches below the
ceiling and at least 12 inches from any corner.
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Heat Sensor - Home security system |
Intruder Detectors
A motion detector functions as
an intruder detector, but other intruder detecting systems are also available.
A typical intruder detection circuit is a closed loop system, meaning that the
entry detection switches are connected in a series. When a protected door or
window is opened, the circuit between the two terminals of the control unit is
broken and the intruder alarm is activated. Several types of switches are available.
Plunger-type switches can be used in wooden door frames or window sashes.
The exact positioning of the switch depends on the type and design of the door
or window. If possible, the switch should be installed in the frame on the
hinge side of a door, and on double-hung windows, both top and bottom sections
should be protected.
Remember, the mounting area must
be large enough to accommodate the flange of the switch. Magnetic operated reed switch assemblies are available for
horizontal or vertical surface mounting on wood or metal door frames or window
sashes. Install the magnetic section on the door or window and the switch on the
frame or sash. Use caution when installing reed switches because they are
easily damaged if dropped, use shims if necessary to install them, and be sure
they are parallel and flush.
An inside shunt switch is used
to bypass switches used in doors and windows. This type of switch is surface mounted
and connected to bypass the entry detector switch. Exit/entry control units
include inside and outside switch plate assemblies to be installed on
21/2-inch-deep single-gang wall boxes, above the reach of small children. The
indicator lights will burn at a somewhat lower level when operating on the
12-volt DC power supply activated by failure of the 120-volt supply.
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Wiring Diagram - Home Security System |
New models rely on a
light-emitting diode (LED) for low power consumption. Figure shows the location
of inside-outside switches. The wiring diagram shows that changing the position
of either S1 or S2 bypasses the entry detector switch and turns the indicator lights
off so that the door can be opened without activating the alarm. The system can
then be rearmed by changing the position of S1 or S2.
Pushbuttons for Emergencies
A manually operated push button for
emergency operation of the fire detection circuit should be installed near the
outside (including basement) doors on the knob side at a height convenient for adults
but out of the reach of small children. Such pushbuttons may also be installed
in bedrooms or other areas where emergency operation of the alarm is desired.
Warning Devices – Home Security Alarm System
An alarm bell is a warning device.
Surface-mounted units should be installed in a central area for greatest
coverage throughout the house. The intercom can be connected so that the alarm
is broadcast throughout the house when the speakers are on. Wiring to an
outside bell should be hidden if possible. Wiring that is exposed should be run
in a conduit, or a waterproof cable should be used. In the system illustrated, the
alarm circuit to energize the bell is approximately 15-volts DC, with normal
120-volts AC supplied to the control unit.
When there is no 120-volt
supply, the emergency unit (e.g., an auxiliary power or battery charger) is in
operation. This voltage will be about 11 volts from the battery. Therefore, any
warning device, such as a bell, has to be able to operate on a 10- to 16-volt range.
Auxiliary Power/Battery Charger
A complete security alarm
system should have an auxiliary power source or battery charger so that
the system can operate in situations where the normal 120-volt power supply is
cut off.
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A typical alarm bell |
A Typical Wireless Security Alarm System
A number of wireless security alarm
systems are available. Most have standard parts that can be programmed to operate
in a number of different configurations. The installation instructions that
come with the system indicate how the system is to be wired.
Parts of The Wireless Security Alarm System
A
typical
microcomputer-based system has about eight fully programmable zones, plus
keypad and fire, police, and medical emergency functions. Each installation may
be custom-designed to meet specific requirements. These alarm systems
are nonvolatile electrically erasable read-only memory (EEROM) chips to store
all data.
This memory is retained even
during complete power failures. All programming is accomplished by entering
data through remote digital keypads. These keypads are available in different
styles, providing flexibility in system design. Some include a speaker that may
be used as an indoor siren and/or an intercom station.
The control panel houses the
electronics for controlling the burglary or fire system and the digital
communicator. The communicator itself is also keypad-programmable and may be
programmed for most transmission formats. The control panel also contains a 12-volt
DC, 1.5-ampere power supply that will provide 900 milliamperes of power for
auxiliary devices.
Entry Delay Lines
Each zone in the system may be
programmed for two entry times (from 000 to 225 seconds duration). After a time
is programmed into each delay time’s memory location, each separate zone may
then be programmed for entry delay time #1 or #2. For example, a long delay
time (#1) might be used for a garage door to allow sufficient time for car
entry or exit, whereas a shorter delay time (#2) would be programmed for front
door entry.
Loop Response Time
The system may also be
programmed for fast or slow loop response times, or how long it takes for the
switch on or off condition to be acted upon by the control unit. These range
from 40 milliseconds to 10 seconds in 40 millisecond increments. After the fast
and slow loop response times are programmed, each separate zone may then be
programmed for slow or fast loop response time.
Keyswitch Zones
If the application calls for
arm/disarm control from a keyswitch, the system may be programmed for a
key-switch zone (a zone operated by using a key to turn a switch). Through keypad
programming, the installer assigns one zone as a key-switch zone. This then can
be controlled by a momentary normally open or a momentary normally closed
key-switch. In some cases, a key operated switch is desired for the garage door
or a gate.
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Remote Digital Keypad |
Bypassing Zones
Zones may be individually
bypassed (shunted) with a two-keystroke operation at the remote control keypad.
All manually bypassed zones are cleared when the system is disarmed. They must
then be bypassed again before the system is armed. Zones cannot be bypassed
once the system is armed. For special applications, fire zones may be
programmed to be shuntable. The digital communicator can also be programmed to
send a bypassed zone arming report to the central station.
Fire Zones and Day Zones
Both fire zones and day zones
sound an audible pre-alarm for a trouble condition. The user can easily silence
a fire pre-alarm at the keypad by pressing the CLEAR key, while an LED will
remain blinking to remind the user that a trouble condition exists.
Alarm Outputs
A number of alarm outputs may be
wired to operate two on-board auxiliary relays. The burglar alarm output can be
programmed to be steady or pulsing. The auxiliary relay outputs can be
connected to a self-contained siren, a two-tone siren driver, or an eight-tone
siren driver.
Alarm outputs can be programmed
to provide a 1 second siren or bell test upon arming the system. To extend the
system’s capability, the alarm outputs can be wired directly to a siren driver
with “trigger inputs” (such as the eight-tone driver), freeing the onboard auxiliary
relays for other tasks.
A typical electronic system can
also be programmed for silent or audible alarms. There are separate outputs for
burglary, fire, police, and medical. Each can be individually programmed for a
cut-off time of 0.001 to 255 minutes or for continuous operation. A lamp output
terminal is activated for 2 minutes each time a key is pressed during entry and
exit delay and during any alarm condition. It can be used as light control for
a hall light or other applications.
Arm/Disarm Codes
Most systems have arm/disarm
codes and a master programming code that can be changed by the user. The codes
can be one to five digits long and digits may be repeated. Each of the
arm/disarm codes in the system illustrated can be programmed to be
1.
An
arm/disarm code only.
2.
An
access code only.(The system includes an access control feature that can be
used for an electric door release or oilier device. The access control output
is timed. It is programmable for 1 to 254 seconds in duration)
3.
An
arm/disarm code if “1” is entered first; an access code if “0” is entered
first.
4.
Arm/disarm
and access simultaneously.
5.
Same
as (4), plus just “0” and code allows access.
6.
A
duress code.
The fourth code (4 listed earlier) can be programmed to function for a
predetermined number of times (1 to 254). This code may be used to allow entry
by housekeeping and service personnel, and the like. After the code is used the
allowed number of times it will no longer work.
Most security alarm systems
also include a programmable short-arming feature that allows one- or two-digit
arming. If the first digit of an arm/disarm code is “0” then one-button arming
is possible just enter “1.” This feature also allows all other command keys to function simply
by pressing the desired command key. However, the full code must be entered to
disarm the system.
Burglary Alarms
A burglary causes an audible
pre-alarm. An alarm causes the ARMED LED to flash. Entering the arm/disarm code
silences the audible pre-alarm, but the flashing LED remains on. Pressing the
CLEAR button resets the flashing LED. During an alarm, entry of an arm/disarm
code will abort the digital communicator unless the code is a distress code. A
fire or medical alarm can be silenced by pressing the CLEAR key.
Fire Alarms
Fire alarms can be silenced by
entering an arm/disarm code by pressing the CLEAR key. The fire zone LED remains
on for an alarm or remains blinking for a trouble condition. If a trouble
condition clears itself, the FIRE LED automatically resets. The FIRE alarm LED
can be cleared by entering the arm/disarm code.
When a fire alarm is silenced by
pressing the CLEAR key, this does not reset the smoke detectors. After
the smoke detector that caused the alarm has been identified (by viewing
the alarm memory LEDs on the smoke detectors), pressing the SMOKE RESET key and
the arm/disarm code interrupts power to the smoke detectors for 5 seconds,
resetting them. SMOKE RESET also performs a battery test. It removes AC power
from the control panel and dynamically tests the battery. If the battery fails the
test, the POWER LED will flash. A low-battery condition will be reported to the
central station. The flashing POWER LED can be reset only by a subsequent test
that recognizes a good battery.
Installing The Wireless Security Alarm System
The panel box of a typical wireless
alarm system is easily mounted and contains the terminal strips required to
complete all of the pre-wiring and terminal wiring connections. The terminal
strips themselves are marked for identification. All input connections are made
on one terminal strip. All output connections are made on the other. This
arrangement allows the installer to complete the pre-wiring, make the terminal connections,
and then safely lock the box.
The main circuit board is a separate
module. It is mounted with four hex screws. The board is mounted to the terminal strips and is simply plugged in
with one connector. This arrangement allows for pre-wiring and protects the electronics from damage during wiring.
Once the installation and wiring
are complete, power is supplied by a flip of the power switch. This eliminates
the need to disconnect the power wiring during installation or service. When
the system is powered up, the installer may program the system directly from
digital remote control keypads. Programming worksheets (complete with zone
identification, programming memory locations, and factory program values) are
provided to aid the installer in programming. A detailed programming manual is
also provided.
After the programming is
complete, the installation can be checked out from the keypad. The installer
simply uses the system status LEDs, the zone status command key, and the
detector check key to verify the system installation. Then all user operations
can be performed to verify the correctness of the program.
Troubleshooting The Wireless Alarm System
In a typical eight-zone system,
the alarm memory function automatically reduces troubleshooting by one-eighth.
Simply pressing the alarm memory command key reveals the zones last alarmed. Then,
within that zone, the detector check command key may be used to troubleshoot
specific detectors. For example, a typical system may contain 45 contacts, and
the keypad can be used to troubleshoot the entire installation. With a
conventional one-zone system, it would be necessary to troubleshoot most of the
45 contacts by trial and error.
Personal Security Alarm System
There are a number of personal
alarm systems today. Personal safety is of primary concern to everyone. At the
top of the security equipments list, whether it be personal security, home
security, or industrial security, alarm systems are, in fact, everybody’s
concern. Some of the alarm systems can be carried with you or installed easily
on doors, windows, and sliding doors as well. Solid, state of the art designs
make these alarm systems the most popular choice among effective security
products.
Personal alarms are attractive,
compact, and easy to carry. You can travel with these alarms on your belt or in
your purse and use the accessories provided to turn them into portable door or window
alarms. This is where the need for an electrician becomes necessary. Once the
alarm has been installed as a permanent device located in a fixed position,
there is usually the need for electrical power and proper set up to make it
work properly.
For instance, infrared motion
alarms use passive infrared technology to produce an invisible barrier that
cannot be penetrated without setting off the alarm. It is usually
battery-operated and requires no wiring, no matter how many times you change
its location. This variety of alarm system functions by detecting motion in any
selected area. The electrician is called to do the job of installing it in a
permanent home. The wiring and the testing for proper operation is the job of
the electrician.
Magnetic door or window alarms
are meant for use on any kind of door or window, even the sliding doors.
Activated by opening the door or window, this alarm uses magnetic affinity to
let off a loud siren. These are usually installed while the house is being built.
In some cases, they have to be installed after the house is already framed and
enclosed. This calls for some skill on the part of the person doing the
installation.
Window glass breakage alarms are
another important alarm system. This alarm has a very loud siren that is
activated by the vibrations caused when someone breaks the glass. You can
install it yourself on any window or have it permanently installed by an electrician.
The electronic barking dog
alarms are used by utilizing microwave technology to “see” through walls. Like
some police radar systems, it can sense if someone is approaching. When the person
comes within a range of 20 feet, the alarm is activated and starts barking. It
sounds as if a German shepherd is in the house.
Alarms in Hazardous Locations
In the installation of alarms,
it is necessary to follow the guidelines offered by the NEC’s latest edition.
The National Electrical Code includes ‘the alarm system’ in a hazardous
location under Article 501-14. Nearly all signaling, remote-control, and
communication equipment involves make or break contacts: hence in Division 1 locations
all devices must be explosion-proof, and the wiring must comply with the
requirements for light and power wiring in such locations, including seals. The
Red Book lists signal devices that include fire alarms and fire
detectors.
Read More:
- Troubleshoot The Home Wiring Problems
- Electrical Troubleshooting For Home Problems
- Home Electrical Installation Maintenance Guide
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