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Fire alarm system
An automatic fire alarm system is designed to detect the unwanted presence of fire by monitoring environmental changes associated with combustion. A fire alarm system is either classified as automatic, manually activated, or both. It is used to notify people to evacuate in the event of a fire or other emergency, to summon emergency services, and to prepare the structure and associated systems to control the spread of fire and smoke
Fire alarm control panel: This component, the hub of the system, monitors inputs and system integrity, control outputs and relays information.
Secondary (backup) Power supplies: This component, commonly consisting of sealed lead-acid storage batteries or other emergency sources including generators, is used to supply energy in the event of a primary power failure
Initiating Devices: This component acts as input to the fire alarm control unit and are either manually or automatically activated.
Notification appliances: This component uses energy supplied from the fire alarm system or other stored energy source, to inform the proximate persons of the need to take action, usually to evacuate.
Building Safety Interfaces: This interface allows the fire alarm system to control aspects of the built environment and to prepare the building for fire and to control the spread of smoke fumes and fire by influencing air movement, lighting, process control, human transport and exit. What is intercom?
Intercom carries the voice signals through the conductors through a wired system.
Types of Intercoms
- Wiring intercoms
- Two wire broadcast intercoms
- Four wire broadcast intercoms
- Wireless intercoms
- Integrated intercoms
- Wiring Intercoms
- While every intercom product line is different, most analogue intercom systems have much in common. Voice signals of about a volt or two are carried atop a direct current power rail of 12, 30 or 48 volts which uses a pair of conductors. Signal light indications between stations can be accomplished through the use of additional conductors or can be carried on the main voice pair via tone frequencies sent above or below the speech frequency range. Multiple channels of simultaneous conversations can be carried over additional conductors within a cable or by frequency- or time-division multiplexing in the analogue domain. Multiple channels can easily be carried by packet-switched digital intercom signals.
- Portable intercoms are connected primarily using common shielded, twisted pair microphone cabling terminated with 3-pin XLR connectors. Building and vehicle intercoms are connected in a similar manner with shielded cabling often containing more than one twisted pair.
- Two Wire Broadcast Intercoms
Intercom systems are widely used in TV stations and outside broadcast vehicles such as those seen at sporting events or entertainment venues. There are essentially two different types of intercoms used in the television world: two-wire party line or four-wire matrix systems. In the beginning, TV stations would simply build their own communication systems using old phone equipment. However, today there are several manufacturers offering off-the-shelf systems. From the late 70's until the mid 90's the two-wire party line type systems were the most popular, primarily due to the technology that was available at the time. The two channel variety used a 32 Volt impedance generating central power supply to drive external stations or belt packs. This type of format allowed the two channels to operate in standard microphone cable, a feature highly desired by the broadcasters. These systems were very robust and simple to design, maintain and operate but had limited capacity and flexibility as they were usually hardwired. A typical user on the system could not choose who to talk to. He would communicate with the same person or group of people until the system was manually reconfigured to allow communication with a different group of people. Two-wire routers or source assignment panels were then implemented to allow quick re-routing of a two-wire circuit. This reconfiguration was usually handled at a central location, but because voltage is used on the circuit to power the external user stations as well as communicate, there would usually be a pop when the channels were switched. So while one could change the system on-the-fly, it was usually not desirable to do so in the middle of a production, as the popping noise would distract to the rest of the production crew
- Four Wire Broadcast Intercoms
- A modern four-wire intercom system capable of 272 sources and destinations manufactured by Telex Communications Inc.
- In the mid-90s four-wire technology started gaining more prominence due to the technology getting cheaper and smaller. Four-wire circuit technology had been around for quite some time but was very expensive to implement. It usually required a large footprint in the physical television studio, thus was only used at very large stations or TV networks. Also, the large physical size made it virtually impossible to use on a mobile platform such as an outside broadcast vehicle. The term four-wire comes from the fact that the system uses a transmit pair and a receive pair for the audio to and from the intercom, i.e. four wires. That said, in a modern four-wire system there are actually six to eight wires: two (or four) for data and the remaining four for audio. There are also a few manufacturers that use digital audio techniques in the form of fiber or coax cable. Nevertheless, the four wire phrase has stuck, and it is the accepted term for this kind of system today. One major advantage of four-wire vs. the two-wire systems is the ability to perform point to point communication at will. Point to point communication allows a user to speak directly to another user similar to how someone would call another person directly using a phone. This ability is extremely useful in today's complex production environments. The difference between a phone system, however, and a four-wire intercom is the ability to not only perform point to point but also point to multi-point, party-lines, interrupt fold back (IFB) and many other configurations, which are useful to the production environment. It should be noted that four-wire systems are essentially audio routers. This makes them very useful not only for the communications aspect of a production, but also routing of audio for confidence monitoring or actual on-air use. In the past, forms of communications such as IFB, audio monitoring and, point to point all had to be separate systems. In the modern four-wire intercom system, these forms of communications are typically all in one compact package. Today the tables have turned, making a four-wire system cheaper and easier to implement than a two-wire system
- Wireless Intercoms
- For installations where it is not desirable or possible to run wires to support an intercom system, wireless intercom systems are available. There are two major benefits of a wireless intercom system over the traditional wired intercom. The first is that installation is much easier since no wires have to be run between intercom units. The second is that you can easily move the units at any time. With that convenience and ease of installation comes a risk of interference from other wireless and electrical devices. Nearby wireless devices such as cordless telephones, wireless data networks, and remote audio speakers can interfere. Electrical devices such as motors, lighting fixtures and transformers can cause noise. There may be concerns about privacy since conversations may be picked up on a scanner, baby monitor, cordless phone, or a similar device on the same frequency. Encrypted wireless intercoms can reduce or eliminate privacy risks, while placement, installation, construction, grounding and shielding methods can reduce or eliminate the detrimental effects of external interference. The United States and Canada have several frequency ranges for wireless intercom systems and other wireless products. They are 49 MHz, FM band (200KH - 270 kHz), 494-608 MHz, 900 MHz, 2.4 GHz, 5.8 GHz, and MURS (150 MHz).
- Power line communication units that send signal over house wiring have been referred to as "wireless" intercoms. Though they are technically wired intercoms, they are based on existing wiring and thus require no additional wires.
- Integrated Intercom Systems
- An integrated intercom system has the capacity to work in conjunction with other security devices and systems thus enabling to “multiply the forces” of any given security system. Integrated intercom systems and solutions work their security "magic" from a distance by covering supplementary areas, allowing communication with any visitor, providing an access control security layer, restricting areas and many other tasks.
- Such integration between intercom security solutions and other integrated security systems improve efficiency, flexibility and security at affordable costs that fit most families' budgets.
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