A battery room is a room in a facility used to house batteries for backup or uninterruptible power systems. Battery rooms are found in telecommunication central offices, to provide standby power to computing equipment in datacenters. Batteries provide direct current electricity, which may be used directly by some types of equipment, or which may be converted to alternating current by uninterruptible power supply equipment; the batteries may provide power for minutes, hours or days depending on the electrical system design, although most the batteries power the UPS during brief electric utility outages lasting only seconds. Battery rooms were used to segregate the fumes and corrosive chemicals of wet cell batteries from the operating equipment. In 1890 the Western Union central telegraph office in New York City had 20,000 wet cells primary zinc-copper type, in use. Telephone system central offices contain large battery systems to provide power for customer telephones, telephone switches, related apparatus.
Terrestrial microwave links, cellular telephone sites, fibre optic apparatus and satellite communications facilities have standby battery systems, which may be large enough to occupy a separate room in the building. In normal operation power from the local commercial utility operates telecommunication equipment, batteries provide power if the normal supply is interrupted; these can be sized for the expected full duration of an interruption, or may be required only to provide power while a standby generator set or other emergency power supply is started. Batteries used in battery rooms are the flooded lead-acid battery, the valve regulated lead-acid battery or the nickel–cadmium battery. Batteries are installed in groups. Several batteries are wired together in a series circuit forming a group providing DC electric power at 12, 24, 48 or 60 volts. There are two or more groups of series-connected batteries; these groups of batteries are connected in a parallel circuit. This arrangement allows an individual group of batteries to be taken offline for service or replacement without compromising the availability of uninterruptible power.
The larger the battery room's electrical capacity, the larger the size of each individual battery and the higher the room's DC voltage. Battery rooms are found in electric power plants and substations where reliable power is required for operation of switchgear, critical standby systems, black start of the station. Batteries for large switchgear line-ups are 125 V or 250 V nominal systems, feature redundant battery chargers with independent power sources. Separate battery rooms may be provided to protect against loss of the station due to a fire in a battery bank. For stations that are capable of black start, power from the battery system may be required for many purposes including switchgear operations. Large utility batteries may be used for grid energy storage. Battery rooms are found on diesel-electric submarines, where they contain the lead-acid batteries used for undersea propulsion of the vessel. Nuclear submarines contain large battery rooms as backups to provide maneuvering power if the nuclear reactor is shut down.
Batteries in surface vessels may be contained in a battery room. Battery rooms on ocean-going vessels must prevent seawater from contacting battery acid, as this could produce toxic chlorine gas; this is of particular concern on submarines. Since several types of secondary batteries give off hydrogen if overcharged, ventilation of a battery room is critical to maintain the concentration below the lower explosive limit; the number of air changes per hour required to prevent unsafe accumulation can be calculated from the number of cells and the charging current, given the chemistry of the battery. The life span of secondary batteries is reduced at high temperature and the energy storage capacity is reduced at low temperature, so a battery room must have heating or cooling to maintain the proper temperature. Batteries may contain large quantities of corrosive electrolytes such as sulfuric acid used in lead-acid batteries or caustic potash used in NiCad batteries. Materials of the battery room must contain any accidental spills.
Plant personnel must be protected from spilled electrolyte. In some jurisdictions, large battery systems may contain reportable amounts of sulfuric acid, a concern for fire departments. Battery rooms in industrial and utility installations have an eye-wash station or decontamination showers nearby, so that workers who are accidentally splashed with electrolyte can wash it away from the eyes and skin. List of battery types Kusko, Alexander. Emergency/Standby Power Systems, pp. 99–117. New York: McGraw-Hill Book Co. ISBN 0-07-035689-0. National Fire Protection Association.'NFPA 111: Standard on Stored Electrical Energy Emergency and Standby Power'
A telephone exchange is a telecommunications system used in the public switched telephone network or in large enterprises. An exchange consists of electronic components and in older systems human operators that interconnect telephone subscriber lines or virtual circuits of digital systems to establish telephone calls between subscribers. In historical perspective, telecommunication terms have been used with different semantics over time; the term telephone exchange is used synonymously with central office, a Bell System term. A central office is defined as a building used to house the inside plant equipment of several telephone exchanges, each serving a certain geographical area; such an area has been referred to as the exchange. Central office locations may be identified in North America as wire centers, designating a facility from which a telephone obtains dial tone. For business and billing purposes, telephony carriers define rate centers, which in larger cities may be clusters of central offices, to define specified geographical locations for determining distance measurements.
In the United States and Canada, the Bell System established in the 1940s a uniform system of identifying central offices with a three-digit central office code, used as a prefix to subscriber telephone numbers. All central offices within a larger region aggregated by state, were assigned a common numbering plan area code. With the development of international and transoceanic telephone trunks driven by direct customer dialing, similar efforts of systematic organization of the telephone networks occurred in many countries in the mid-20th century. For corporate or enterprise use, a private telephone exchange is referred to as a private branch exchange, when it has connections to the public switched telephone network. A PBX is installed in enterprise facilities collocated with large office spaces or within an organizational campus to serve the local private telephone system and any private leased line circuits. Smaller installations might deploy a PBX or key telephone system in the office of a receptionist.
In the era of the electrical telegraph, post offices, railway stations, the more important governmental centers, stock exchanges few nationally distributed newspapers, the largest internationally important corporations and wealthy individuals were the principal users of such telegraphs. Despite the fact that telephone devices existed before the invention of the telephone exchange, their success and economical operation would have been impossible on the same schema and structure of the contemporary telegraph, as prior to the invention of the telephone exchange switchboard, early telephones were hardwired to and communicated with only a single other telephone. A telephone exchange is a telephone system located at service centers responsible for a small geographic area that provided the switching or interconnection of two or more individual subscriber lines for calls made between them, rather than requiring direct lines between subscriber stations; this made it possible for subscribers to call each other at businesses, or public spaces.
These made telephony an available and comfortable communication tool for everyday use, it gave the impetus for the creation of a whole new industrial sector. As with the invention of the telephone itself, the honor of "first telephone exchange" has several claimants. One of the first to propose a telephone exchange was Hungarian Tivadar Puskás in 1877 while he was working for Thomas Edison; the first experimental telephone exchange was based on the ideas of Puskás, it was built by the Bell Telephone Company in Boston in 1877. The world's first state-administered telephone exchange opened on November 12, 1877 in Friedrichsberg close to Berlin under the direction of Heinrich von Stephan. George W. Coy designed and built the first commercial US telephone exchange which opened in New Haven, Connecticut in January, 1878; the switchboard was built from "carriage bolts, handles from teapot lids and bustle wire" and could handle two simultaneous conversations. Charles Glidden is credited with establishing an exchange in Lowell, MA. with 50 subscribers in 1878.
In Europe other early telephone exchanges were based in London and Manchester, both of which opened under Bell patents in 1879. Belgium had its first International Bell exchange a year later. In 1887 Puskás introduced the multiplex switchboard.. Exchanges consisted of one to several hundred plug boards staffed by switchboard operators; each operator sat in front of a vertical panel containing banks of ¼-inch tip-ring-sleeve jacks, each of, the local termination of a subscriber's telephone line. In front of the jack panel lay a horizontal panel containing two rows of patch cords, each pair connected to a cord circuit; when a calling party lifted the receiver, the local loop current lit a signal lamp near the jack. The operator responded by inserting the rear cord into the subscriber's jack and switched her headset into the circuit to ask, "Number, please?" For a local call, the operator inserted the front cord of the pair into the called party's local jack and started the ringing cycle. For a long distance call, she plugged into a trunk circuit to connect to another operator in another bank of boards or at a remote central office.
In 1918, the average time to complete the connection for a long-distance call was 15 minutes. Early manual switchboards required the operator to operate listening keys and ringing keys, but by the late 1910s and 1920s, advances in switchboard technology led to features which allowed the call to be automatic
Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is one joule per second. Electric power is produced by electric generators, but can be supplied by sources such as electric batteries, it is supplied to businesses and homes by the electric power industry through an electric power grid. Electric power is sold by the kilowatt hour, the product of the power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter, which keeps a running total of the electric energy delivered to a customer. Electrical power provides a low entropy form of energy and can be carried long distances and converted into other forms of energy such as motion, light or heat with high energy efficiency. Electric power, like mechanical power, is the rate of doing work, measured in watts, represented by the letter P; the term wattage is used colloquially to mean "electric power in watts." The electric power in watts produced by an electric current I consisting of a charge of Q coulombs every t seconds passing through an electric potential difference of V is P = work done per unit time = V Q t = V I where Q is electric charge in coulombs t is time in seconds I is electric current in amperes V is electric potential or voltage in volts Electric power is transformed to other forms of energy when electric charges move through an electric potential difference, which occurs in electrical components in electric circuits.
From the standpoint of electric power, components in an electric circuit can be divided into two categories: Passive devices or loads: When electric charges move through a potential difference from a higher to a lower voltage, when conventional current moves from the positive terminal to the negative terminal, work is done by the charges on the device. The potential energy of the charges due to the voltage between the terminals is converted to kinetic energy in the device; these devices are called passive loads. Examples are electrical appliances, such as light bulbs, electric motors, electric heaters. In alternating current circuits the direction of the voltage periodically reverses, but the current always flows from the higher potential to the lower potential side. Active devices or power sources: If the charges are moved by an'exterior force' through the device in the direction from the lower electric potential to the higher, work will be done on the charges, energy is being converted to electric potential energy from some other type of energy, such as mechanical energy or chemical energy.
Devices in which this occurs are called active devices or power sources. Some devices can current through them. For example, a rechargeable battery acts as a source when it provides power to a circuit, but as a load when it is connected to a battery charger and is being recharged, or a generator as a power source and a motor as a load. Since electric power can flow either into or out of a component, a convention is needed for which direction represents positive power flow. Electric power flowing out of a circuit into a component is arbitrarily defined to have a positive sign, while power flowing into a circuit from a component is defined to have a negative sign, thus passive components have positive power consumption, while power sources have negative power consumption. This is called the passive sign convention. In the case of resistive loads, Joule's law can be combined with Ohm's law to produce alternative expressions for the amount of power, dissipated: P = I V = I 2 R = V 2 R, where R is the electrical resistance.
In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power; that portion of power flow due to stored energy, that returns to the source in each cycle, is known as reactive power. The real power P in watts consumed by a device is given by P = 1 2 V p I p cos θ = V r m s I r m s cos θ where Vp is the peak voltage in volts Ip is the peak current in amperes Vrms is the root-mean-square voltage in volts Irms is the root-mean-square current in amperes θ is the phase angle between the current and voltage sine waves The relationship between real power, reactive power and apparent power can be expressed by representing the quantities as vectors. Real power is represented as a horizontal vector and reactive power is represented as a vertical vector.
The apparent power vector is the hypotenuse o
An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components. Electronic components leads; these leads connect to create an electronic circuit with a particular function. Basic electronic components may be packaged discretely, as arrays or networks of like components, or integrated inside of packages such as semiconductor integrated circuits, hybrid integrated circuits, or thick film devices; the following list of electronic components focuses on the discrete version of these components, treating such packages as components in their own right. Components can be classified as active, or electromechanic; the strict physics definition treats passive components as ones that cannot supply energy themselves, whereas a battery would be seen as an active component since it acts as a source of energy.
However, electronic engineers who perform circuit analysis use a more restrictive definition of passivity. When only concerned with the energy of signals, it is convenient to ignore the so-called DC circuit and pretend that the power supplying components such as transistors or integrated circuits is absent, though it may in reality be supplied by the DC circuit; the analysis only concerns the AC circuit, an abstraction that ignores DC voltages and currents present in the real-life circuit. This fiction, for instance, lets us view an oscillator as "producing energy" though in reality the oscillator consumes more energy from a DC power supply, which we have chosen to ignore. Under that restriction, we define the terms as used in circuit analysis as: Active components rely on a source of energy and can inject power into a circuit, though this is not part of the definition. Active components include amplifying components such as transistors, triode vacuum tubes, tunnel diodes. Passive components can't introduce net energy into the circuit.
They can't rely on a source of power, except for what is available from the circuit they are connected to. As a consequence they can't amplify, although they may increase current. Passive components include two-terminal components such as resistors, capacitors and transformers. Electromechanical components can carry out electrical operations by using moving parts or by using electrical connectionsMost passive components with more than two terminals can be described in terms of two-port parameters that satisfy the principle of reciprocity—though there are rare exceptions. In contrast, active components lack that property. Conduct electricity in one direction, among more specific behaviors. Diode, diode bridge Schottky diode – super fast diode with lower forward voltage drop Zener diode – passes current in reverse direction to provide a constant voltage reference Transient voltage suppression diode, unipolar or bipolar – used to absorb high-voltage spikes Varicap, tuning diode, variable capacitance diode – a diode whose AC capacitance varies according to the DC voltage applied.
Light-emitting diode – a diode that emits light Photodiode – passes current in proportion to incident light Avalanche photodiode – photodiode with internal gain Solar Cell, photovoltaic cell, PV array or panel – produces power from light DIAC, Trigger Diode, SIDAC) – used to trigger an SCR Constant-current diode Peltier cooler – a semiconductor heat pump Tunnel diode - fast diode based on quantum mechanical tunneling Transistors were considered the invention of the twentieth century that changed electronic circuits forever. A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. Transistors Bipolar junction transistor – NPN or PNP Photo transistor – amplified photodetector Darlington transistor – NPN or PNP Photo Darlington – amplified photodetector Sziklai pair Field-effect transistor JFET – N-CHANNEL or P-CHANNEL MOSFET – N-CHANNEL or P-CHANNEL MESFET HEMT Thyristors Silicon-controlled rectifier – passes current only after triggered by a sufficient control voltage on its gate TRIAC – bidirectional SCR Unijunction transistor Programmable Unijunction transistor SIT SITh Composite transistors IGBT Digital electronics Analog Hall effect sensor – senses a magnetic field Current sensor – senses a current through it Opto-electronics Opto-isolator, opto-coupler, photo-coupler – photodiode, BJT, JFET, SCR, TRIAC, zero-crossing TRIAC, open collector IC, CMOS IC, solid state relay Slotted optical switch, opto switch, optical switch LED display – seven-segment display, sixteen-segment display, dot-matrix display Current: Filament lamp Vacuum fluorescent display Cathode ray tube (monochro
Telephony is the field of technology involving the development and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is intimately linked to the development of the telephone. Telephony is referred to as the construction or operation of telephones and telephonic systems and as a system of telecommunications in which telephonic equipment is employed in the transmission of speech or other sound between points, with or without the use of wires; the term is used to refer to computer hardware and computer network systems, that perform functions traditionally performed by telephone equipment. In this context the technology is referred to as Internet telephony, or voice over Internet Protocol; the first telephones were connected directly in pairs. Each user had a separate telephone wired to the locations he or she might wish to reach; this became inconvenient and unmanageable when people wanted to communicate with more than a few people.
The inventions of the telephone exchange provided the solution for establishing telephone connections with any other telephone in service in the local area. Each telephone was connected to the exchange via the local loop. Nearby exchanges in other service areas were connected with trunk lines and long distance service could be established by relaying the calls through multiple exchanges. Switchboards were manually operated by an attendant referred to as the "switchboard operator"; when a customer cranked a handle on the telephone, it turned on an indicator on the board in front of the operator, who would plug the operator headset into that jack and offer service. The caller had to ask for the called party by name by number, the operator connected one end of a circuit into the called party jack to alert them. If the called station answered, the operator disconnected their headset and completed the station-to-station circuit. Trunk calls were made with the assistance of other operators at other exchangers in the network.
In modern times, most telephones are plugged into telephone jacks. The jacks are connected by inside wiring to a drop wire. Cables bring a large number of drop wires from all over a district access network to one wire center or telephone exchange; when a telephone user wants to make a telephone call, equipment at the exchange examines the dialed telephone number and connects that telephone line to another in the same wire center, or to a trunk to a distant exchange. Most of the exchanges in the world are interconnected through a system of larger switching systems, forming the public switched telephone network. After the middle of the 20th century and data became important secondary users of the network created to carry voices, late in the century, parts of the network were upgraded with ISDN and DSL to improve handling of such traffic. Today, telephony uses digital technology in the provisioning of telephone systems. Telephone calls can be provided digitally, but may be restricted to cases in which the last mile is digital, or where the conversion between digital and analog signals takes place inside the telephone.
This advancement has reduced costs in communication, improved the quality of voice services. The first implementation of this, ISDN, permitted all data transport from end-to-end speedily over telephone lines; this service was made much less important due to the ability to provide digital services based on the IP protocol. Since the advent of personal computer technology in the 1980s, computer telephony integration has progressively provided more sophisticated telephony services and controlled by the computer, such as making and receiving voice and data calls with telephone directory services and caller identification; the integration of telephony software and computer systems is a major development in the evolution of office automation. The term is used in describing the computerized services of call centers, such as those that direct your phone call to the right department at a business you're calling. It's sometimes used for the ability to use your personal computer to initiate and manage phone calls.
CTI is not a new concept and has been used in the past in large telephone networks, but only dedicated call centers could justify the costs of the required equipment installation. Primary telephone service providers are offering information services such as automatic number identification, a telephone service architecture that separates CTI services from call switching and will make it easier to add new services. Dialed Number Identification Service on a scale is wide enough for its implementation to bring real value to business or residential telephone usage. A new generation of applications is being developed as a result of standardization and availability of low cost computer telephony links. Starting with the introduction of the transistor, invented in 1947 by Bell Laboratories, to amplification and switching circuits in the 1950s, through development of computer-based electronic switching systems, the public switched telephone network has evolved towards automation and digitization of signaling and audio transmissions.
Digital telephony is the use of digital electronics in the operation and provisioning of telephony systems and services. Since the 1960s a digital core network has replaced the traditional analog transmission and signaling systems, much of the access network has been digitized. Digital
Telecommunication is the transmission of signs, messages, writings and sounds or information of any nature by wire, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology, it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is used in its plural form because it involves many different technologies. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, loud whistles. 20th- and 21st-century technologies for long-distance communication involve electrical and electromagnetic technologies, such as telegraph and teleprinter, radio, microwave transmission, fiber optics, communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse, Alexander Graham Bell, Edwin Armstrong and Lee de Forest, as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth; the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, the Latin communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was first used as an English word in the late 14th century, it comes from Old French comunicacion, from Latin communicationem, noun of action from past participle stem of communicare "to share, divide out.
Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots, was used by the Romans to aid their military. Frontinus said; the Greeks conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Sumatra, and in 1849, Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of beacons were used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London. In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris.
However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres. As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. On 25 July 1837 the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke, English scientist Sir Charles Wheatstone. Both inventors viewed their device as "an improvement to the electromagnetic telegraph" not as a new device. Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837, his code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was completed on 27 July 1866, allowing transatlantic telecommunication for the first time; the conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849.
However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean; this was the start of wireless telegraphy by radio. Voice and music had little early success. World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar. Development of stereo FM broadcasting of radio