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
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active ...
. Its use became widespread in the early 21st century, replacing the basic closed-circuit system, mainly because of changes in international standards and practices.
Mandatory UK standard
{{webarchive , url=https://web.archive.org/web/20081121033020/http://www.preventcrime.co.uk/en50131.html , date=November 21, 2008
Dual-loop allows the burglar alarm control panel
A security alarm is a system designed to detect intrusion, such as unauthorized entry, into a building or other areas such as a home or school. Security alarms used in residential, commercial, industrial, and military properties protect against ...
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 ohm
Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm.
Ohm or OHM may also refer to:
People
* Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm''
* Germán Ohm (born 1936), Mexican boxer
* Jörg Ohm (bo ...
s 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
Series may refer to:
People with the name
* Caroline Series (born 1951), English mathematician, daughter of George Series
* George Series (1920–1995), English physicist
Arts, entertainment, and media
Music
* Series, the ordered sets used i ...
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
A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit ...
or open-circuit, an anti-tamper alarm will trigger.
Dual loop is more commonly known as Balanced EOL (End of Line) resistors. It is more secure than the former Double Pole loop, but nevertheless can be bypassed by someone with sufficient knowledge of security alarm systems.
References
External links
Calculators for resistors in series and parallel.
Analog circuits