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The Electricity Guy: Don`t Be Alarmed

Updated on July 7, 2017

Understanding the Modern Alarm Panel

Modern panels are quite complex and generally have many peripherals attached.

In this article, 'The Electricity Guy' will take a closer look at how these panels work.

There are several indicators on the panel, plus a large display.

To understand better, we need to focus on the five main states that a fire panel can be in. These are: Normal State, Monitor Cue, Trouble Cue, Supervisory Cue, and Alarm State.

Normal State is where the panel will almost always be. In this state, the display will show, 'SYSTEM NORMAL', plus the current date and time. There should also be an indicator showing that the unit is getting power, usually a green LED with the label 'A/C ON'.

Monitor Cue is the first state that indicates there is a problem somewhere in the system. There will usually be a yellow LED next to 'MONITOR' and the display will show what device needs attention, along with the current date and time. The panel will also be beeping to indicate a problem. However, in this state, the panel can be silenced. The monitor cue is generally for small problems that usually don`t affect the overall operation of the fire detection system, but could eventually if not fixed.

Trouble Cue is a more serious state that indicates a problem with one or more of the fire suppression devices. These devices include sprinklers and carbon dioxide extinguishers. In this state the panel will beep with a yellow LED next to `TROUBLE` and the display will show the device affected, the zone or area the device is located as well as the current date and time. In this state the panel can be silenced temporarily.

Supervisory Cue is a condition where a supervised device needs attention. These are fire detection units. These include, smoke detectors, heat detectors, sprinkler flow detectors, and the manual pull stations. Although the manual stations are not really detectors, they are included in this group. When a supervisory cue is activated, the panel will beep with a yellow LED next to `SUPERVISOR`. The display will show the device and the zone where the device is located, plus the current date and time. In this state the panel can be silenced temporarily.

Alarm State is a bit different. In addition to the panel beeping, it also will activate the lights and audible alarm throughout the building. A red LED will flash next to 'ALARM', and the display will show the activated device, its location, and the time and date the alarm was activated. In buildings with elevators, the system will automatically bring all cars to the ground floor and open the doors. With the exception of an alarm on the ground floor, the cars will stop on the second floor. In either case, none of the cars will respond to any operation. In this state the panel can not be silenced. The system must be reset by the fire chief.

It is also important to note that an Alarm state does not mean there is a fire. It means that one of the fire detectors is reporting a problem. In most cases it is simply a faulty device. For example, sprinkler flow detectors are prone to failure. However, when you hear and see an alarm activated it is important to be alert and listen for instructions. The building security and the fire department will investigate, and provide information about the alarm over the PA.


The example below shows an actual alarm panel in three cues all at the same time. In this case, the Alarm takes priority. The time and date on the display are when the alarm was activated.

Fire alarm panel in an unusual simultaneous trouble, supervisory, and alarm state caused by a faulty sprinkler flow detector.
Fire alarm panel in an unusual simultaneous trouble, supervisory, and alarm state caused by a faulty sprinkler flow detector.

Fire Detection Units

There are primarily four different types of fire detectors

Smoke Detector Unit is connected to the panel and will send an alert signal to the panel when smoke is detected. Do not touch one of these devices, as it could cause an activation.

Heat Detector Unit is connected to the panel and will send an alert when a sudden and extreme increase in temperature is detected. Do not touch one of these devices, as it could cause an activation.

Sprinkler Flow Detector Units are inside the sprinkler pipes. It will send a signal to the panel when water flow through the pipe is detected.

Manual Stations are located throughout the building and are connected to the panel and send an alert when the handle is pulled down. In most jurisdictions, it is illegal to activate a manual station unless a fire is detected. Do not touch a pull station unless there is a real emergency.

Modern smoke detector unit.
Modern smoke detector unit.
Modern heat detector unit.
Modern heat detector unit.

Sprinkler Systems

The sprinklers are not part of the alarm panel, but are connected to it via the sprinkler flow detectors.

The sprinkler heads themselves contain a glass tube that is heat sensitive. When the tube breaks, the sprinkler activates.

There are two types of sprinkler systems, a wet pipe system and a dry pipe system.

Wet pipe is the simplest system. These have water in the pipes all the time and the water flows out when a sprinkler is activated. The flow detector then sends a signal to the panel.

Dry pipe is a bit more complicated. This system is used in places that are unheated, such as underground parking areas. Obviously, water can not remain in the pipes, otherwise it could freeze and cause damage to the pipes. Instead of water, these pipes contain air. At the base of the system is a flapper valve. On the opposite side of the valve is water. A compressor keeps the air pressure in the pipes the same as the water pressure. If the pressure of the air and water is not the same, the flap will open and allow water to leak into the system. With this system, when a sprinkler is activated, air comes out first. The air pressure drops, the flap opens, then comes the water. The flow detector then sends a signal to the panel.

You can tell the difference between a wet and dry system by the way the sprinkler heads are pointing. If the heads point downward, it is a wet pipe system. However, with a dry pipe system, the heads point upward.


Dry pipe sprinkler head.
Dry pipe sprinkler head.
Dry pipe sprinkler system showing flapper valve and compressor.
Dry pipe sprinkler system showing flapper valve and compressor.
Close up of compressor.
Close up of compressor.
Close up of flapper valve.
Close up of flapper valve.
Wet pipe sprinkler head.
Wet pipe sprinkler head.


That is all for this entry from 'The Electricity Guy'.

Look out for more about electricity and electronics right here from 'The Electricity Guy'.

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