Dual loop
Encyclopedia
This article refers to the electrical circuit as used in burglar alarms. Several other uses for the term "Dual loop" may also exist.
Dual-loop is a method of electrical circuit termination used in electronic security applications, particularly modern intruder alarms
. It is called 'dual-loop' because two circuits (alarm and anti-tamper) are combined into one using resistors. It has become widespread in use over the last few years replacing the basic closed-circuit system, mainly because of changes in international standards and practices.
to read the values of end-of-line resistors for the purpose of telling a zone's status. For example: if an alarm system's software uses 2K ohms
as its non-alarm value, an inactive detector will give a reading of 2K ohms as the circuit is passing through just one resistor. When the detector goes into an active state (i.e. a door contact being opened), the circuit path has been altered and it must now pass through a second resistor wired in series with the first. This gives a reading of 4K ohms and will trigger an intruder alarm. If a resistance reading is not recognised by the system either due to short-circuit
or open-circuit, an anti-tamper alarm will trigger.
Dual-loop is a method of electrical circuit termination used in electronic security applications, particularly modern intruder alarms
Burglar alarm
Burglar , alarms are systems designed to detect unauthorized entry into a building or area. They consist of an array of sensors, a control panel and alerting system, and interconnections...
. It is called 'dual-loop' because two circuits (alarm and anti-tamper) are combined into one using resistors. It has become widespread in use over the last few years replacing the basic closed-circuit system, mainly because of changes in international standards and practices.
Method
Dual-loop allows the burglar alarm control panelBurglar alarm control panel
A burglar alarm control panel is a wall-mounted unit where the detection devices and wiring of the alarm are ultimately connected and managed. These include devices such as bells, sirens, door contacts, motion detectors, smoke detectors, etc. Typical panels are located in utility closets or access...
to read the values of end-of-line resistors for the purpose of telling a zone's status. For example: if an alarm system's software uses 2K ohms
Ohms
OHMS may refer to:* The plural of ohm, a unit of resistance, named after Georg Ohm* Ohm's Law of electric currents, first proposed by Georg Ohm* O.H.M.S., On His/Her Majesty's Service...
as its non-alarm value, an inactive detector will give a reading of 2K ohms as the circuit is passing through just one resistor. When the detector goes into an active state (i.e. a door contact being opened), the circuit path has been altered and it must now pass through a second resistor wired in series with the first. This gives a reading of 4K ohms and will trigger an intruder alarm. If a resistance reading is not recognised by the system either due to short-circuit
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
or open-circuit, an anti-tamper alarm will trigger.