Misplaced Pages

Burglar alarm control panel: Difference between revisions

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.
Browse history interactively← Previous editContent deleted Content addedVisualWikitext
Revision as of 00:43, 5 January 2006 editVegaswikian (talk | contribs)270,510 edits two articles on same topic?← Previous edit Latest revision as of 05:31, 9 September 2017 edit undoSteel1943 (talk | contribs)Autopatrolled, Extended confirmed users, Page movers, Pending changes reviewers, Rollbackers, Template editors197,090 edits #REDIRECT Security alarm#Design {{R with history}} {{R to section}} - subject is not notable independent of the subject security alarm 
(61 intermediate revisions by 52 users not shown)
Line 1: Line 1:
#REDIRECT ]
{{mergewith|Burglar alarm keypad}}
{{R with history}} {{R to section}}
A '''burglar alarm control panel''' is a panel that is used to control a ].

The simplest type of burglar alarm control consists of one relay. In this type, the
sensor circuit (called the ''loop'' in industrial terminology) holds a relay energized.
Since the path for the loop goes through a set of contacts which are normally open (when
the relay is restored they are open, when the relay is energized they are closed), when the
loop opens, even momentarily, the relay will drop out and stay that way. A second set of
contacts on the relay, normally closed (when the relay is restored they are closed, when
the relay is energized they are open) is used to operate the annunciator, usually a bell.
The system is disarmed by a key operated shunt which forces the relay to energize, and is
armed by closing all traps and then by opening the key operated shunt. While burglar alarm
controls are now very elaborate, the single-relay control incorporates all the functionality
of any control. These controls and a closely related dual-relay design are still widely used
in stand-alone applications, powered by carbon cells.

In a modern full-functional control there are two, possibly three classifications of
loop, and each classification of loop has two types. The classifications of loop are
''instant'' and ''delay'', and ''day'' loops. The types of loops are single-circuit and
double-circuit. In modern controls there may be several instant and/or day loops, but there
is usually only one delay loop. Depending on the control, any loop may be single-circuit
or double-circuit.

The loop types will be discussed first. If we refer to the prototypical single-relay
control, the current comes from the battery on the positive or ''high'' side, goes through
the relay and the latching circuit, and then back to the battery on the negative or ''low''
side. Since the loop is a series circuit (all contacts are closed when the points they are
protecting are secured and they are therefore wired into a series circuit) there are two
places in the circuit where the loop can be inserted. The loop can be inserted on the high
side, between the battery and the relay, or it may be inserted on the low side, between the
relay and the return. If the loop is taken out to the protection only once, then the system
is a single-loop system and the other side of the loop is simply strapped at the control. If
both the high side and the low side of the loop are taken out to the protection, then the
system is a double-loop system.

The advantage of the single loop system is lower cost and lower complexity. However,
the disadvantage of the single loop system used in our example is that by strapping across
the contact, an intruder could open a hole in the protection and thereby defeat the system.
The double loop system, while it is more expensive, does not have this disadvantage, as an
attempt to strap across the contact can also strap across the relay, dropping it out and
tripping the system.

The three classifications of loops as mentioned above are instant, delay, and day
circuits. In our example there is only one loop, the instant loop. Not all controls have
all classifications of loops.
The ''instant'' loop is armed as soon as the control is armed, and any loop violation,
no matter how transient, will cause an immediate trip.
The ''delay'' loop, found primarily in controls designed for use with keystations
located within the protected area, does not arm as soon as the control is armed. Instead,
there is a delay of nominally 45 seconds before this loop arms, to allow the person arming
the control time to clear the protected area. Also, when the protected point covered by the
delay loop is opened, the control will not go into alarm for nominally 45 seconds, to allow
the person entering time to go to the keystation and disarm the system.
The ''day'' loop is a supervisory circuit for protection such as window bugs, tampers,
and window foil. If this loop is violated when the control is armed the result will be that
the system will trip and the control goes into alarm. If this loop is violated when the control
is not armed the result will be that a supervisory alarm, or ''trouble'' alarm will be
signaled.

Modern alarm controls are solid-state devices and do not use relays. The front end
for the loop is usually a double op-amp comparator sensing a current flow through the
protection. Because the loop resistance can be up to a couple of hundred ohms at installation,
and because resistance transients can occur which are not the result of a loop violation, there
is usually a fair bit of tolerance as to the limits of the current flow which are considered
normal operation. The current is set by an end-of-line resistor located at the contact for the
point being protected. If the loop is opened, the current will decrease to zero and the control
will go into alarm. If the contact is strapped across, the current will increase (the control
incorporates current limiting to prevent damage) and the control will go into alarm.

Early (c.a. 1980) solid-state alarm controls used shunt switches or momentary closures on
the key circuit to arm or disarm the control. Modern controls can use these arming techniques,
but more frequently use a keypad which sends operating information to the control. Thus, there
is no point in attacking the keypad, as there is no intelligence in the keypad, it is all located
in the control. Also, many controls feature integrated transmitters, using wired telephony or
optionally, cellular telephony. These controls also monitor the status of the telephone line,
and can be programmed to trip if the telephone line fails (or is cut). The controls which utilize
cellular telephony report either periodically or at a pseudo-random interval to the central
station, and a failure to report will result in a dispatch.

High-security alarm controls use current and impedance monitoring on the premises, and may
report to the central station via dedicated voice-grade or DC (obsolescent) circuit, or by means
of multiple-drop AC grade transmitter (multiplex).

AH 051210







{{electro-stub}}

]

Latest revision as of 05:31, 9 September 2017

Redirect to:

  • With history: This is a redirect from a page containing substantive page history. This page is kept as a redirect to preserve its former content and attributions. Please do not remove the tag that generates this text (unless the need to recreate content on this page has been demonstrated), nor delete this page.
    • This template should not be used for redirects having some edit history but no meaningful content in their previous versions, nor for redirects created as a result of a page merge (use {{R from merge}} instead), nor for redirects from a title that forms a historic part of Misplaced Pages (use {{R with old history}} instead).