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In the case of a fire alarm, 6 mA could be normal, 15 mA could mean a fire has been detected, and 0 mA would produce a trouble indication, telling the monitoring site the alarm circuit had failed. Some devices, such as two-way radio remote control consoles, can reverse the polarity of currents and can multiplex audio onto a DC current.
Coded panels were the earliest type of central fire alarm control, and were made during the 1800s to the 1970s. A coded panel is similar in many ways to a modern conventional panel (described below), except each zone was connected to its own code wheel, which, depending on the way the panel was set up, would either do sets of four rounds of code until the initiating pull station was reset ...
It consists of a repeated three-pulse cycle (0.5 s on, 0.5 s off, 0.5 s on, 0.5 s off, 0.5 s on, 1.5 s off). Voice evacuation is the second most common audible notification in modern systems. Legacy systems, typically found in older schools and buildings, have used continuous tones alongside other audible notifications.
In its simplest form, the user activates the alarm by pulling the handle down, which completes a circuit and locks the handle in the activated position, sending an alarm to the fire alarm control panel. After operation, most fire alarm pull stations must be restored to the ready position using a special tool or key for the panel to be reset.
Fire alarm call box (Somerville, Massachusetts) A fire alarm box, fire alarm call box, or fire alarm pull box is a device used for notifying a fire department of a fire or a fire alarm activation. Typically installed on street corners or on the outside of commercial buildings in urban areas, they were the main means of summoning firefighters ...
An Autocall C-2000 panel. This panel was the 2 zone variant of the C-series conventional fire alarm panels released by Autocall in the late 1990s. When Thorn was purchased by Tyco-owned Grinnell in 1996, their systems were branded under "Grinnell/Autocall". [5]
According to NFPA 72-2010, section 18.4.5.3*, audible appliances provided for sleeping areas to awaken occupants shall produce a mid frequency alarm signal that complies with the following (effective January 1, 2014): (1) The alarm signal shall be a square wave or provide equivalent awakening ability.
The NFPA 72 (National Fire Alarm and Signaling Code) is a standard published by the National Fire Protection Association every 3 years for installation of fire alarm systems and emergency communication systems in the United States.