Photoelectric smoke detectors utilize a light source and a photosensitive cell. The introduction of smoke into that ionized air will reduce the amount of current and cause an alarm signal. Ionization smoke detectors utilize a small amount of radioactive material to ionize air molecules into positively and negatively charged molecules that create a small electric current. These types of initiating device circuits are known as analog addressable as they are able to tell the FACU their address and their value. #GT AUTO ALARM MANUAL SOFTWARE#And then the control unit software determines the set points for initiation of an alarm, supervisory, or trouble signal. When one initiating device is activated on a signaling line circuit, the FACU is still able to poll the other devices unlike a conventional initiating device circuit.Īdditionally, some addressable initiating devices are able to also transmit to the FACU a range of values of smoke density, temperature variation, water level, water pressure changes, and other variables. The device address allows for the location of the detector to be identified at the FACU. When the FACU polls an initiating device, the initiating device responds with its status (Normal, Alarm, ect.) and address. This identification consists of a binary string of 1s and 0s that indicate the address or location of that device on the circuit. Zones are typically designed to enable someone to easily identify an area where the alarm is located, for example, in a school you may have a gymnasium zone circuit and an auditorium zone circuit that each contain multiple devices.Īddressable devices are either initiating devices or control/notification appliances that are capable of communicating a unique identification number or address to a control unit via a signaling line circuit. Because of this, any device on the circuit or “zone” will put the entire zone into an alarm state. Once one device shorts the circuit, no other device on that circuit or “zone” can send a signal. By doing so, the initiating device causes an increase in current flowing through the circuit, which the FACU interprets as an alarm signal. Based on the type of detectors and FACU, the signals can be sent over an initiating device circuit (IDC) for conventional systems, or a signaling line circuit (SLC) for addressable systems.Ĭonventional initiating devices are typically detectors that use a switch contact to short both sides of the initiating device circuit together. Depending on the system, the signal from an initiating device can create an alarm condition or a supervisory condition. The components include all devices and circuits that send a signal to a fire alarm control unit (FACU) such as heat detectors, smoke detectors, carbon monoxide detectors, water flow switches, manually actuated devices, and pressure switches. The main function of the initiation portion of a fire alarm system is to report the status of a protected space or the existence of a fire. This blog will take a deeper dive into the initiation portion of a fire alarm system. For an overview of the entire system take a look at my Guide to Fire Alarm Basics Blog. #GT AUTO ALARM MANUAL SERIES#The objective of this blog series is to discuss some of the major components and functions of a fire alarm system. A fire alarm system serves many functions and the differences between the functions can be a bit confusing, so I created a visual guide to fire alarm basics. A fire alarm system is a crucial part of the overall fire protection and life safety strategy of a building.
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