Specifications

All rights reserved by MONACOR
®
INTERNATIONAL GmbH & Co. KG.
A reproduction of this catalogue – or any parts thereof – for any commercial use is prohibited.
KNOW-HOW: Alarm Technology
KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW
S95
Alarm Systems
Today, both sales rooms and private households are more and more
secured by electronic alarm systems.
Two methods are used: apart from the classic wired alarm system
where each alarm device is connected to an alarm lead, wireless alarm
systems are used, too. At such systems, the alarm device is connected
to the alarm centre via radio contact. The alarm device transmits a
special code in order to achieve a high safety level against tampering
of the radio contact. Only if the alarm centre receives the code which
has been learned at the installation, an alarm is triggered. The alarm
device is almost solely operated via built-in long-life batteries, thus al-
most no wiring is required. This is particularly important in private
households, because the experience shows that an alarm system is in
most cases retrofitted after a house has been built or the renovation of
a flat has been finished. The transmission range of the transmitter is
quite high and thus an alarm centre can be installed in adjoining
rooms. The few leads which are required for power, outdoor siren, and
maybe a telephone dialling unit are usually not a problem in such
rooms.
There are different methods for securing an object.
Indoor protection
Individual or all rooms of a building are secured by motion detectors.
If the alarm centre has been activated, none of the rooms can be en-
tered without triggering an alarm. This method is always required if a
person would be able to hide inside the building before the alarm sys-
tem has been activated.
Peripheral protection
This method is generally used for dwelling houses. All entries to the
house, like windows and doors are secured by contacts. Thus, it is pos-
sible to activate the alarm system and at the same time move freely in-
side the house. By attaching the contacts to windows and doors, the
alarm is already triggered when these have only been opened
approx. 2
cm. If the contacts are attached to the bottom of the window,
it is even possible to tilt the window for fresh air without deactivating
the alarm system.
Full protection
This is a combination of both methods mentioned above. Light barriers
for outdoor applications or video motion detection can additionally be
used which present further safety elements.
NOTE: Some alarm systems, e.g. MAX-20MC, make acknowledge-
ment signals when they are activated or deactivated. If the
alarm centre is installed in adjoining rooms or in the cellar,
the system can hardly be heard if activated from the out-
side. In this case, it is recommended to install a basic buz-
zer which is connected in parallel to the internal buzzer of
the alarm centre.
NC, NO, stand-by loop
In connection with the inputs of a wired alarm centre, the terms NC
contact, NO contact as well as stand-by loop are mentioned time and
again. These terms describe the switching behaviour in case of an
alarm.
NC = normally closed Normally closed contact
This is a contact which is normally closed in
stand-by mode.
An alarm is triggered when this contact is
opened.
All contacts within a loop are connected in
parallel.
Disadvantage of an NC contact: If the alarm lead is short-circuited, all
contacts behind the short circuit are ineffective.
NO = normally open Normally open contact
This is a contact which is normally opened
in stand-by mode.
An alarm is triggered when this contact is
closed.
All contacts within a loop are connected in
parallel.
Disadvantage of an NO contact: If the alarm lead is disconnected, all
contacts are ineffective.
Stand-by loop
The alarm leads of sole NC or NO loops can easily be tampered with
and thus modern alarm systems feature stand-by loops which use an
additional resistor (R) in order to monitor the status of the alarm con-
tacts. This resistor is connected to the alarm lead at the spot furthest
away.
In stand-by mode:
all NO contacts are
open and all NC
contacts are closed,
the resistor is con-
nected directly to the
input.
The alarm centre registers the value and the deviation from the de-
sired value. If the value at the connections is outside the tolerance
threshold, e.g. when an NO contact is closed (short circuit) or when
an NC contact is open (disconnection), an alarm is triggered.
Thus it is ensured, that a disconnection or a short circuit of an alarm
lead triggers an alarm after activating the alarm centre.
Anti-tampering contacts
Additional anti-tampering loops are con-
nected in order to recognise a tampering
at the motion detectors or leads immedi-
ately. These are wire loops or e.g. cover
contacts of motion detectors which are con-
nected in parallel.
These contacts are connected to a special
loop of the alarm centre which cannot be activated; i.e. this input
monitors these anti-tampering loops 24 hours a day. If a motion de-
tector is opened or a lead is tampered with, an anti-tampering alarm
is triggered; independently of the alarm centre being active or inactive.
NC
SABOTAGE
NC
NO
R
NO
NC