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4-20mA
In electrical signalling an analog current loop is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time. A major application of current loops is the industry de facto standard 4–20 mA current loop for process control applications, where they are extensively used to carry signals from process instrumentation to proportional–integral–derivative (PID) controllers, supervisory control and data acquisition (SCADA) systems, and programmable logic controllers (PLCs). They are also used to transmit controller outputs to the modulating field devices such as control valves. These loops have the advantages of simplicity and noise immunity, and have a large international user and equipment supplier base. Some 4–20 mA field devices can be powered by the current loop itself, removing the need for separate power supplies, and the "smart" Highway Addressable Remote Transducer (HART) Protoc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
De Facto Standard
A ''de facto'' standard is a custom or convention that is commonly used even though its use is not required. is a Latin phrase (literally " of fact"), here meaning "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established". A ''de facto'' standard contrasts an international standard which is defined by an organization such as International Standards Organization, or a standard required by law (also known as ''de jure'' standards). Joint technical committee on information technology (ISO/IEC JTC1) developed a procedure in order for de facto standards to be processed through the formal standardization system to be transformed into international standards from ISO and IEC. In social sciences a voluntary standard that is also a ''de facto'' standard is a typical solution to a coordination problem. The choice of a ''de facto'' standard tends to be stable in situations in which all parties can realize mutual gains, but only by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Instrumentation
Instrumentation is a collective term for measuring instruments, used for indicating, measuring, and recording physical quantities. It is also a field of study about the art and science about making measurement instruments, involving the related areas of metrology, automation, and control theory. The term has its origins in the art and science of Scientific instrument, scientific instrument-making. Instrumentation can refer to devices as simple as direct-reading thermometers, or as complex as multi-sensor components of industrial control systems. Instruments can be found in laboratories, refineries, factories and vehicles, as well as in everyday household use (e.g., smoke detectors and thermostats). Measurement parameters Instrumentation is used to measure many parameters (physical values), including: *Pressure, either Differential pressure transducer, differential or static pressure, static *Rate of fluid flow, Flow *Temperature measurement, Temperature *Level Measurement, L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Control Valves
A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level. In automatic control terminology, a control valve is termed a "final control element". Operation The opening or closing of automatic control valves is usually done by electrical, hydraulic or pneumatic actuators. Normally with a modulating valve, which can be set to any position between fully open and fully closed, valve positioners are used to ensure the valve attains the desired degree of opening. Air-actuated valves are commonly used because of their simplicity, as they only require a compressed air supply, whereas electrically operated valves require additional cabling and switch gear, and hydraulically actuated valves required high pressure supply and return lines for the hydraulic fluid. The p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dry Pair
A dry loop is an unconditioned leased pair of telephone line from a telephone company. The pair does not provide dial tone or battery (continuous electric potential), as opposed to a wet pair, a line usually without dial tone but with battery. A dry pair was originally used with security systems but more recently may also be used with digital subscriber line (DSL) service or an Ethernet extender to connect two locations, as opposed to a costlier means such as a Frame Relay. The pair in many cases goes through the local telephone exchange. ''Wet pair'' naming comes from the battery used to sustain the loop, which was made from wet cells. Many carriers market dry loops to independent DSL providers as a BANA for basic analog loop or in some locales PANA for plain analog loop, OPX (off-premises extension) line, paging circuit, or finally LADS (local area data service). Local availability In the United States, these circuits typically incur a monthly recurring charge of $3.00 per ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell System
The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the AT&T Corporation, American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America for over 100 years from its creation in 1877 until United States v. AT&T (1982), its antitrust breakup in 1983. The system of companies was often colloquially called Ma Bell (as in "Mother Bell"), as it held a vertical monopoly over telecommunication products and services in most areas of the United States and Canada. At the time of the breakup of the Bell System in the early 1980s, it had assets of $150 billion (equivalent to $ billion in ) and employed over one million people. Beginning in the 1910s, American antitrust regulators had been observing and accusing the Bell System of abusing its monopoly power, and had brought legal action multiple times over the decades. In 1974 the United States Department of Justice Antitrust Division, Anti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Two-way Radio
A two-way radio is a radio transceiver (a radio that can both transmit and receive radio waves), which is used for bidirectional person-to-person voice communication with other users with similar radios, in contrast to a broadcast receiver, which only receives transmissions. Two-way radios usually use a half-duplex communication channel, which permits two-way communication, albeit with the limitation that only one user can transmit at a time. (This is in contrast to simplex communication, in which transmission can only be sent in one direction, and full-duplex, which allows transmission in both directions simultaneously.) This requires users in a group to take turns talking. The radio is normally in receive mode so the user can hear all other transmissions on the channel. When the user wants to talk, they press a " push-to-talk" button, which turns off the receiver and turns on the transmitter; when the button is released, the receiver is activated again. Multiple channels are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siren (noisemaker)
A siren is a noise-making warning device. There are two general types: mechanical sirens and electronic sirens. Civil defense sirens are mounted in fixed locations and used to warn of natural disasters or attacks. Sirens are used on emergency service vehicles such as ambulances, police cars, and fire engines. Many fire sirens (used for summoning volunteer firefighters) serve double duty as tornado or civil defense sirens, alerting an entire community of impending danger. Most fire sirens are either mounted on the roof of a fire station or on a pole next to the fire station. Fire sirens can also be mounted on or near government buildings, on tall structures such as water towers, as well as in systems where several sirens are distributed around a town for better sound coverage. Most fire sirens are single tone and mechanically driven by electric motors with a rotor attached to the shaft. Some newer sirens are Electronics, electronically driven speakers. Fire sirens are often cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Traffic Signals
Traffic lights, traffic signals, or stoplights – also known as robots in South Africa, Zambia, and Namibia – are signaling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control the flow of traffic. Traffic lights usually consist of three signals, transmitting meaningful information to road users through colours and symbols, including arrows and bicycles. The usual traffic light colours are red to stop traffic, Amber (color), amber for traffic change, and green to allow traffic to proceed. These are arranged vertically or horizontally in that order. Although this is internationally standardised, variations in traffic light sequences and laws exist on national and local scales. Traffic lights were first introduced in December 1868 on Parliament Square in London to reduce the need for police officers to control traffic. Since then, electricity and computerised control have advanced traffic light technolog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal (electrical Engineering)
A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing'' includes audio, video, speech, image, sonar, and radar as examples of signals. A signal may also be defined as observable change in a quantity over space or time (a time series), even if it does not carry information. In nature, signals can be actions done by an organism to alert other organisms, ranging from the release of plant chemicals to warn nearby plants of a predator, to sounds or motions made by animals to alert other animals of food. Signaling occurs in all organisms even at cellular level ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Base Station
Base station (or base radio station, BS) is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a " land station in the land mobile service." A base station is called '' node B'' in 3G, '' eNB'' in LTE ( 4G), and '' gNB'' in 5G. The term is used in the context of mobile telephony, wireless computer networking and other wireless communications and in land surveying. In surveying, it is a GPS receiver at a known position, while in wireless communications it is a transceiver connecting a number of other devices to one another and/or to a wider area. In mobile telephony, it provides the connection between mobile phones and the wider telephone network. In a computer network, it is a transceiver acting as a switch for computers in the network, possibly connecting them to a/another local area network and/or the Internet. In traditional wireless communications, it can refer to the hub of a dispatch fleet such as a taxi or delivery fl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pl Control Valve
PL, P.L., Pl, or .pl may refer to: Businesses and organizations Government and political * Partit Laburista, a Maltese political party * Liberal Party (Brazil, 2006), a Brazilian political party * Liberal Party (Moldova), a Moldovan political party * Liberal Party (Rwanda), a Rwandan political party * Parlamentarische Linke, a parliamentary caucus in Germany * Patriotic League (Bosnia and Herzegovina) (Bosnian: ''Patriotska Liga''), a military organisation of the Republic of Bosnia and Herzegovina * Philippine Legislature, a legislature that existed in the Philippines from 1907 to 1935 * Progressive Labor Party (United States), a United States communist party Sports leagues * Palestine League, the top Palestinian football league * Premier League, the top English football league * Pacific League, one of the two leagues in Japan's Nippon Professional Baseball * Pioneer Baseball League, a Rookie league in American Minor League Baseball * Pioneer Football League, NCAA FCS confe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
