Coded Fire Alarm Control Panels
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 ( i.e. An alarm in zone 1 would sound code 1-2-4, while zone 2 would sound 1-2-5), 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 (similar to a coded pull station) or run continuously until the panel itself was reset. Large panels could take up an entire wall in a mechanical room, with dozens of code wheels. Lists of codes had to be maintained, sometimes with copies posted above pull stations (this setup is commonly seen in older wings of hospitals). Smaller panels could be set up in one of two ways. Most of the time, the panel would only have one zone, and therefore, only one code. Common one-zone codes were 4-4-0 and 17-0-0 (which is similar to the 120 bpm March Time setting used on later panels, which has in turn been replaced with an interrupted four count uniform temporal code 3 pattern used since 1996). Alternatively, the panel could be made with no code wheels, using only what was called the gong relay. Normally, this would be used in a system with coded pull stations to retransmit the coding strikes from the pulls. However, it could also be used as its own zone, with the connected horns or bells sounding continuously instead of in a particular code. These panels are not common today, but can sometimes be found in older buildings such as those on college campuses or hospitals.
Today, there are two types of fire panels:
1. Conventional fire alarm panel; 2. Addressable fire alarm panel
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—Lewis Thomas (b. 1913)
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