feedback loop

Feedback is a process in which information about the past or the present influences the same phenomenon in the present or future. As part of a chain of cause-and-effect that forms a circuit or loop, the event is said to "feed back" into itself. Ramaprasad (1983) defines feedback generally as "information about the gap between the actual level and the reference level of a system parameter which is used to alter the gap in some way", emphasizing that the information by itself is not feedback unless translated into action.[1] "...'feedback' exists between two parts when each affects the other..."[2](p53) Feedback is also a synonym for: Feedback signal - the measurement of the actual level of the parameter of interest. Feedback mechanism - the action or means used to subsequently modify the gap. Feedback loop - the complete causal path that leads from the initial detection of the gap to the subsequent modification of the gap. Overview Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter economic theory in Britain by the eighteenth century, but it wasn't at that time recognized as a universal abstraction and so didn't have a name.[3] The verb phrase "to feed back", in the sense of returning to an earlier position in a mechanical process, was in use in the US by the 1860s,[4][5] and in 1909, Nobel laureate Karl Ferdinand Braun used the term "feed-back" as a noun to refer to (undesired) coupling between components of an electronic circuit.[6] By the end of 1912, researchers using early electronic amplifiers (audions) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through regeneration), but would also cause the audion to howl or sing.[7] This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920.[7] There has been over the years some dispute as to the best definition of feedback. According to Ashby, mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of "circularity of action", which keeps the theory simple and consistent. For those with more practical aims, feedback should be a deliberate effect via some more tangible connexion. "[Practical experimenters] object to the mathematician's definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum ... between its position and its momentum - a 'feedback' that, from the practical point of view, is somewhat mystical. To this the mathematician retorts that if feedback is to be considered present only when there is an actual wire or nerve to represent it, then the theory becomes chaotic and riddled with irrelevancies."[2](p54) [edit]Types of feedback Main articles: negative feedback and positive feedback Feedback is commonly divided into two types - usually termed positive and negative. The terms can be applied in two contexts: the context of the gap between reference and actual values of a parameter, based on whether the gap is widening (positive) or narrowing (negative).[1] the context of the action or effect that alters the gap, based on whether it involves reward (positive) or non-reward/punishment (negative).[8] The two contexts may cause confusion, such as when an incentive (reward) is used to boost poor performance (narrow a gap). Referring to context 1, some authors use alternative terms, replacing 'positive/negative' with self-reinforcing/self-correcting,[9] reinforcing/balancing,[10] discrepancy-enhancing/discrepancy-reducing[11] or regenerative/degenerative[12] respectively. And within context 2, some authors advocate describing the action or effect as positive/negative reinforcement rather than feedback.[1][8] Yet even within a single context an example of feedback can be called either positive or negative, depending on how values are measured or referenced.[13] This confusion may arise because feedback can be used for either informational or motivational purposes, and often has both a qualitative and a quantitative component. As Connellan and Zemke (1993) put it: "Quantitative feedback tells us how much and how many. Qualitative feedback tells us how good, bad or indifferent."[14](p102) The terms "positive/negative" were first applied to feedback prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit.[15] Friis and Jensen (1924) described regeneration in a set of electronic amplifiers as a case where the "feed-back" action is positive in contrast to negative feed-back action, which they mention only in passing.[16] Harold Stephen Black's classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black: "Positive feed-back increases the gain of the amplifier, negative feed-back reduces it."[17] According to Mindell (2002) confusion in the terms arose shortly after this: "...Friis and Jensen had made the same distinction Black used between 'positive feed-back' and 'negative feed-back', based not on the sign of the feedback itself but rather on its effect on the amplifier’s gain. In contrast, Nyquist and Bode, when they built on Black’s work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition."[15](p121) Even prior to the terms being applied, James Clerk Maxwell had described several kinds of "component motions" associated with the centrifugal governors used in steam engines, distinguishing between those that lead to a continual increase in a disturbance or the amplitude of an oscillation, and those which lead to a decrease of the same.[18] [edit]Applications [edit]Biology In biological systems such as organisms, ecosystems, or the biosphere, most parameters must stay under control within a narrow range around a certain optimal level under certain environmental conditions. The deviation of the optimal value of the controlled parameter can result from the changes in internal and external environments. A change of some of the environmental conditions may also require change of that range to change for the system to function. The value of the parameter to maintain is recorded by a reception system and conveyed to a regulation module via an information channel. An example of this is Insulin oscillations. Biological systems contain many types of regulatory circuits, both positive and negative. As in other contexts, positive and negative do not imply consequences of the feedback have good or bad final effect. A negative feedback loop is one that tends to slow down a process, whereas the positive feedback loop tends to accelerate it. The mirror neurons are part of a social feedback system, when an observed action is "mirrored" by the brain - like a self-performed action. Feedback is also central to the operations of genes and gene regulatory networks. Repressor (see Lac repressor) and activator proteins are used to create genetic operons, which were identified by Francois Jacob and Jacques Monod in 1961 as feedback loops. These feedback loops may be positive (as in the case of the coupling between a sugar molecule and the proteins that import sugar into a bacterial cell), or negative (as is often the case in metabolic consumption). On a larger scale, feedback can have a stabilizing effect on animal populations even when profoundly affected by external changes, although time lags in feedback response can give rise to predator-prey cycles.[19] In zymology, feedback serves as regulation of activity of an enzyme by its direct product(s) or downstream metabolite(s) in the metabolic pathway (see Allosteric regulation). Hypothalamo-pituitary-adrenal and gonadal axis is largely controlled by positive and negative feedback, much of which is still unknown. In psychology, the body receives a stimulus from the environment or internally that causes the release of hormones. Release of hormones then may cause more of those hormones to be released, causing a positive feedback loop. This cycle is also found in certain behaviour. For example, "shame loops" occur in persons who blush easily. When they realize that they are blushing, they become even more embarrassed, which leads to further blushing, and so on.[20] [edit]Climate science Main article: Climate change feedback The climate system is characterized by strong positive and negative feedback loops between processes that affect the state of the atmosphere, ocean, and land. A simple example is the ice-albedo positive feedback loop whereby melting snow exposes more dark ground (of lower albedo), which in turn absorbs heat and causes more snow to melt. [edit]Control theory Main article: Control theory Feedback is extensively used in control theory, using a variety of methods including state space (controls), full state feedback (also known as pole placement), and so forth. Note that in the context of control theory, "feedback" is traditionally assumed to specify "negative feedback".[21] Further information: PID controller The most common general-purpose controller using a control-loop feedback mechanism is a proportional-integral-derivative (PID) controller. Heuristically, the terms of a PID controller can be interpreted as corresponding to time: the proportional term depends on the present error, the integral term on the accumulation of past errors, and the derivative term is a prediction of future error, based on current rate of change.[22] [edit]Mechanical engineering In ancient times, the float valve was used to regulate the flow of water in Greek and Roman water clocks; similar float valves are used to regulate fuel in a carburettor and also used to regulate tank water level in the flush toilet. The Dutch inventor Cornelius Drebbel (1572-1633) built thermostats (c1620) to control the temperature of chicken incubators and chemical furnaces. In 1745, the windmill was improved by blacksmith Edmund Lee, who added a fantail to keep the face of the windmill pointing into the wind. In 1787, Thomas Mead regulated the rotation speed of a windmill by using a centrifugal pendulum to adjust the distance between the bedstone and the runner stone (i.e., to adjust the load). The use of the centrifugal governor by James Watt in 1788 to regulate the speed of his steam engine was one factor leading to the Industrial Revolution. Steam engines also use float valves and pressure release valves as mechanical regulation devices. A mathematical analysis of Watt's governor was done by James Clerk Maxwell in 1868.[18] The Great Eastern was one of the largest steamships of its time and employed a steam powered rudder with feedback mechanism designed in 1866 by J.McFarlane Gray. Joseph Farcot coined the word servo in 1873 to describe steam-powered steering systems. Hydraulic servos were later used to position guns. Elmer Ambrose Sperry of the Sperry Corporation designed the first autopilot in 1912. Nicolas Minorsky published a theoretical analysis of automatic ship steering in 1922 and described the PID controller. Internal combustion engines of the late 20th century employed mechanical feedback mechanisms such as the vacuum timing advance but mechanical feedback was replaced by electronic engine management systems once small, robust and powerful single-chip microcontrollers became affordable. [edit]Electronic engineering The simplest form of a feedback amplifier can be represented by the ideal block diagram.[23] The use of feedback is widespread in the design of electronic amplifiers, oscillators, and logic circuit elements. Electronic feedback systems are also very commonly used to control mechanical, thermal and other physical processes. If the signal is inverted on its way round the control loop, the system is said to have negative feedback; otherwise, the feedback is said to be positive. Negative feedback is often deliberately introduced to increase the stability and accuracy of a system by correcting unwanted changes. This scheme can fail if the input changes faster than the system can respond to it. When this happens, the lag in arrival of the correcting signal can result in over-correction, causing the output to oscillate or "hunt".[24] While often an unwanted consequence of system behaviour, this effect is used deliberately in electronic oscillators. Harry Nyquist contributed the Nyquist plot for assessing the stability of feedback systems. An easier assessment, but less general, is based upon gain margin and phase margin using Bode plots (contributed by Hendrik Bode). Design to ensure stability often involves frequency compensation, one method of compensation being pole splitting. Electronic feedback loops are used to control the output of electronic devices, such as amplifiers. A feedback loop is created when all or some portion of the output is fed back to the input. A device is said to be operating open loop if no output feedback is being employed and closed loop if feedback is being used.[25] Negative feedback loops When the fed-back output signal is out of phase with the input signal. This occurs when the fed-back signal is anywhere from 90° to 270° with respect to the input signal. Negative feedback is generally used to correct output errors or to lower device output gain to a pre-determined level. In feedback amplifiers, this correction is generally for waveform distortion reduction or to establish a specified gain level. A general expression for the gain of a negative feedback amplifier is the asymptotic gain model. Positive feedback loops When the fed-back signal is in phase with the input signal. Under certain gain conditions, positive feedback reinforces the input signal to the point where the output of the device oscillates between its maximum and minimum possible states. Positive feedback may also introduce hysteresis into a circuit. This can cause the circuit to ignore small signals and respond only to large ones. It is sometimes used to eliminate noise from a digital signal. Under some circumstances, positive feedback may cause a device to latch, i.e., to reach a condition in which the output is locked to its maximum or minimum state. The loud squeals that sometimes occurs in audio systems, PA systems, and rock music are known as audio feedback. If a microphone is in front of a loudspeaker that it is connected to, sound near the microphone will come out of the speaker, be picked up by the microphone, and get re-amplified. If the loop gain is sufficient, howling or squealing at the maximum power of the amplifier is possible. [edit]Software engineering and computing systems Feedback loops provide generic mechanisms for controlling the running, maintenance, and evolution of software and computing systems.[26] Feedback-loops are important models in the engineering of adaptive software, as they define the behaviour of the interactions among the control elements over the adaptation process, to guarantee system properties at run-time. Feedback loops and foundations of control theory has been successfully applied to computing systems.[27] In particular, they have been applied to the development of products such as IBM's Universal Database server and IBM Tivoli. From a software perspective, the autonomic (MAPE, monitor analyze plan execute) loop proposed by researchers of IBM is another valuable contribution to the application of feedback loops to the control of dynamic properties and the design and evolution of autonomic software systems.[28][29] [edit]Social sciences A feedback loop to control human behaviour involves four distinct stages.[30] Evidence. A behaviour must be measured, captured, and data stored. Relevance. The information must be relayed to the individual, not in the raw-data form in which it was captured but in a context that makes it emotionally resonant. Consequence. The information must illuminate one or more paths ahead. Action. There must be a clear moment when the individual can recalibrate a behavior, make a choice, and act. Then that action is measured, and the feedback loop can run once more, every action stimulating new behaviors that inch the individual closer to their goals. [edit]Reflexive feedback A sociological concept that states a feedback association is created within a certain relationship whereby the subject/object that delivers a stimulus to a second subject/object, will in response receive the stimulus back. This first impulse is reflected back and forth over and over again. [edit]Economics and finance The stock market is an example of a system prone to oscillatory "hunting", governed by positive and negative feedback resulting from cognitive and emotional factors among market participants. For example, When stocks are rising (a bull market), the belief that further rises are probable gives investors an incentive to buy (positive feedback - reinforcing the rise, see also stock market bubble); but the increased price of the shares, and the knowledge that there must be a peak after which the market will fall, ends up deterring buyers (negative feedback - stabilizing the rise). Once the market begins to fall regularly (a bear market), some investors may expect further losing days and refrain from buying (positive feedback - reinforcing the fall), but others may buy because stocks become more and more of a bargain (negative feedback - stabilizing the fall). George Soros used the word reflexivity, to describe feedback in the financial markets and developed an investment theory based on this principle. The conventional economic equilibrium model of supply and demand supports only ideal linear negative feedback and was heavily criticized by Paul Ormerod in his book "The Death of Economics", which, in turn, was criticized by traditional economists. This book was part of a change of perspective as economists started to recognise that chaos theory applied to nonlinear feedback systems including financial markets. [edit]World-system development The hyperbolic growth of the world population observed till the 1970s has recently been correlated to a non-linear second-order positive feedback between the demographic growth and technological development that can be spelled out as follows: technological growth - increase in the carrying capacity of land for people - demographic growth - more people - more potential inventors - acceleration of technological growth - accelerating growth of the carrying capacity - the faster population growth - accelerating growth of the number of potential inventors - faster technological growth - hence, the faster growth of the Earth's carrying capacity for people, and so on.[31] [edit]Education In the majority of universities, teachers decide learning objectives and feedbacks to students.[32] Learners have different conceptions of learning activities and preconceptions about hierarchy in education. Some may look up to instructors as experts in the field and take to heart most of the things instructors say. This is the subject of study in the field of "formative feedback" or "formative assessment".

AM MW Profile

Ampegon Spinnereistrasse 5 5300 Turgi SWITZERLAND Phone : +41 (58) 710 44 00 E-mail : info@ampegon.com Armstrong Transmitter Corporation 4835 North Street Marcellus, NY 13108 U.S.A. Phone : +1 (315) 673-1269 E-mail : info@armstrongtx.com Broadcast Electronics, Inc. 4100 North 24th Street Quincy, IL 62305-3606 U.S.A. Phone : +1 (217) 224-9600 E-mail : bdcast@bdcast.com BT Broadcast Transmitters Rua Sérgio Jungblut Dieterich, 900/21 Porto Alegre - Rio Grande do Sul BRAZIL Phone : +55 (51) 3368-5470 E-mail : bt@bttelecom.com.br Energy-Onix P.O. Box 801, 1306 River Street Valatie, NY 12184 U.S.A. Phone : +1 (518) 758-1690 E-mail : energy-onix@energy-onix.com Harris Broadcast 9800 S Meridian Blvd, Suite 300 Englewood, CO 80112 U.S.A. Phone : +1 (303) 476-5000 E-mail : Nautel Ltd. 10089 Peggy's Cove Road Hackett's Cove, Nova Scotia B3Z 3J4 CANADA Phone : +1 (902) 823-3900 E-mail : info@nautel.com NEC Corporation 7-1, Shiba 5-chome, Minato-ku Tokyo 108-8001 JAPAN Phone : +81 (3) 3798-5463 E-mail : RIZ-Transmitters Co. Bozidareviceva 13 10000 Zagreb CROATIA Phone : +385 (1) 2355-222 E-mail : riz@riz.hr Thomson Broadcast 1, rue de l'Hautil 78700 Conflans Sainte Honorine FRANCE Phone : +33 (1) 34 90 31 00 E-mail : sales@thomson-broadcast.com Transradio SenderSysteme Berlin AG Mertensstrasse 63 13587 Berlin GERMANY Phone : +49 (30) 339 78 0 E-mail : info@tsb-ag.de

AM MW Profile

Ampegon Spinnereistrasse 5 5300 Turgi SWITZERLAND Phone : +41 (58) 710 44 00 E-mail : info@ampegon.com Armstrong Transmitter Corporation 4835 North Street Marcellus, NY 13108 U.S.A. Phone : +1 (315) 673-1269 E-mail : info@armstrongtx.com Broadcast Electronics, Inc. 4100 North 24th Street Quincy, IL 62305-3606 U.S.A. Phone : +1 (217) 224-9600 E-mail : bdcast@bdcast.com BT Broadcast Transmitters Rua Sérgio Jungblut Dieterich, 900/21 Porto Alegre - Rio Grande do Sul BRAZIL Phone : +55 (51) 3368-5470 E-mail : bt@bttelecom.com.br Energy-Onix P.O. Box 801, 1306 River Street Valatie, NY 12184 U.S.A. Phone : +1 (518) 758-1690 E-mail : energy-onix@energy-onix.com Harris Broadcast 9800 S Meridian Blvd, Suite 300 Englewood, CO 80112 U.S.A. Phone : +1 (303) 476-5000 E-mail : Nautel Ltd. 10089 Peggy's Cove Road Hackett's Cove, Nova Scotia B3Z 3J4 CANADA Phone : +1 (902) 823-3900 E-mail : info@nautel.com NEC Corporation 7-1, Shiba 5-chome, Minato-ku Tokyo 108-8001 JAPAN Phone : +81 (3) 3798-5463 E-mail : RIZ-Transmitters Co. Bozidareviceva 13 10000 Zagreb CROATIA Phone : +385 (1) 2355-222 E-mail : riz@riz.hr Thomson Broadcast 1, rue de l'Hautil 78700 Conflans Sainte Honorine FRANCE Phone : +33 (1) 34 90 31 00 E-mail : sales@thomson-broadcast.com Transradio SenderSysteme Berlin AG Mertensstrasse 63 13587 Berlin GERMANY Phone : +49 (30) 339 78 0 E-mail : info@tsb-ag.de

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AM Transmitter

Description An AM voice transmitter with variable tuning. The antenna circuit is also tuned and transmits via a long wire antenna. Please Note. It is illegal to transmit on the AM wavebands in most countries, as such this circuit is shown for educational purposes only. Notes Please read the disclaimer on this site before making any transmitter circuit. It is illegal to operatea radio transmitter without a license in most countries. This circuit is deliberately limited in power output but will provide amplitude modulation (AM) of voice over the range 500kHz to 1600kHz with values shown. You can input values in the calculator below, remember to change drop down box to picofarads for capacitance and microhenries for the coil. The coil is fixed at 200uH, the capacitor values can be varied and resonant frequency found by using the calculator below. Tuned Circuit Resonant Frequency Calculator Capacitance: Inductance: Resonant Frequency: Home Analysis Help Media Links Practical Schematics Simulation Updates Coil Data If winding your own coil then you may find Martin E Meserve page very helpful: Single Layer Air Core Inductor Design An alternative is to use a toroid core of appropriate material. Toroid's come in different sizes and colours, see the sample below. A T130-2 core requires approximately 137 turns of 36 SWG wire. Mike Yancey has a very useful Toroid calculator on his webpage, link below: Toroid Calculator Circuit Notes The circuit is in two parts, a microphone pre-amplifier built around Q1 and an RF oscillator circuit (Q2). The oscillator is a standard Hartley oscillator which is tunable. Tank circuit L1 and C1 control frequency of oscillation, the power in the tank circuit limited via emitter resistor R1. The transmitter output is taken from the collector, L2 and C2 form another tuned tank circuit and help match the antenna. L1,L2, C1 and C2 may be salvaged from an old AM radio if available. The antenna should be a length a wire about 10 feet or more. In the schematic I have shown coaxial cable to be wired to the "longwire" antenna, the outer coax shield returned to ground. Ground in this case is a cold water pipe, however even without a ground and coax cable a signal should still be possible. L2 and C2 not only help match the antenna to the transmitter, but also help remove harmonics and spurious emissions in the transmitter circuit caused by non linearity in the transistors. Q2 needs regenerative feedback to oscillate and this is achieved by connecting the base and collector of Q2 to opposite ends of the tank circuit which is achieved by C4. C3 ensures that the oscillation is passed from collector, to emitter, via the internal base emitter resistance of the transistor, back to the base again. Emitter resistor R1 has two important roles in this circuit. It ensures that the oscillation will not be shunted to ground via the very low internal emitter resistance, re of Q2, and secondly raises input impedance so that the modulation signal will not be shunted. Q1 is wired as a common emitter amplifier, C7 decoupling the emitter resistor and realizing full gain of this stage. Bias of this stage is controlled by R4,R5 and R3. The microphone is an electret condenser type microphone, R7 setting operating current of the ECM and C6 providing DC blocking. The amount of modulation is controlled by the 10k preset resistor PR1 which is also the collector load. The preamp stage is decoupled by R6, C8 and C10. This ensures no high freqency feedback from the oscillator gets into the audio stage. Some electrolytics capacitors have a high impedance at radio frequencies, hence the use of C10, a 10n ceramic to bypass any oscillator frequencies.

FM Transmitter

FM Transmitters, RVR and TV Transmitters When you are looking for an FM transmitter, TV transmitters, audio equipment, editing stations or any TV or radio production equipment, turn to your #1 broadcast provider, the Broadcast Depot. We carry the top name brands you can trust such as Axia, Comrex, Bose, DVX, RVR and Omnia. If you need a high quality TV, AM or FM radio transmitter, you can turn to us. For all of your TV or radio transmission needs, we are your one-stop shop. • FM Exciters and FM Transmitters • RF Transmission Connectors/Accessories • RF Transmission Lines • Dummy Loads • AM Exciters and AM Transmitters • FM Solid State Amplifiers • FM Tube Amplifiers • HD Radio Transmitters • Video Compression Encoders • Video Decoders • Power tubes • Processors • Antennas • Microwaves • Audio Codecs • Metering Equipment • Voltage Protection We can also fully equip your on-air studio and post-production suite. With a wide range of products to choose from such as audio cards, console mixers, players and recorders, Auralex acoustic material, automation/production software, microphones, sound effects machines, telephone equipment, amplifiers, speakers and headphones, you can find exactly what you are looking for without having to search a hundred different places. The staff at Broadcast Depot is knowledgeable and can help you find what you are looking for within the budget you have set. Whether it’s the latest RVR TEX 1000 LCD/S with its Digital user interface or a simple microphone stand, when you want to outfit your production studio, turn to Broadcast Depot.

Honda Generators-inverter

Inverter Generator Advantages What are the benefits of an inverter generator? High quality power output The precision of Honda's inverter technology ensures its power is closer to "line power" more than any other generator design. Our inverter generators produce power that is as reliable as the power you get from your outlets at home. Lighter, smaller size Honda engineers use inverter technology to integrate parts from the engine and the generator. For example, the alternator on our EU1000i, EU2000i, and EU3000iS is combined with the engine flywheel. This allows inverter generators to be smaller and lighter weight than traditional models. High fuel efficiency Eco-Throttle™ allows the generator's engine to automatically adjust the engine speed to produce only the power needed for the application in use. Traditional generators have to run at 3600 RPM to produce 60 hertz (cycle) electricity. But generators with Eco-Throttle can run at much slower RPMs while maintaining frequency and power for the requested load. Because the engine does not have to run at full speed constantly, Eco- Throttle reduces fuel consumption by up to 40%. It also helps to reduce exhaust emissions . Quiet operation Honda's inverter generators are substantially quieter than traditional models. See our decibel chart to get a good idea of the difference. Eco-Throttle also reduces the noise level on our inverter generators. Because the engine is not running at full speed constantly, it is much quieter. Special sound dampening materials and quiet Honda engines also help to make our inverter generators incredibly quiet. Parallel capability EU1000i, EU2000i, EU3000 Handi, and EU3000is generators can be paired with another identically sized unit to double your power capacity. Parallel capability allows you to use two smaller, lighter generators to do the work of a much larger generator - without sacrificing portability. More info on parallel capability How does the inverter work? Honda 's inverter technology takes the raw power produced by the generator and uses a special microprocessor to condition it through a multi-step process. First, the generator's alternator produces high voltage multiphase AC power. The AC power is then converted to DC. Finally the DC power is converted back to AC by the inverter. The inverter also smoothes and cleans the power to make it high quality. A special microprocessor controls the entire process, as well as the speed of the engine. Honda uses only high quality inverters in our generators, which produce stable, consistent power. The end result? Clean enough power to run even the most sensitive electronic equipment. http://powerequipment.honda.com/c ontent/images/pages/generators/gg_CarryEU2000.jpg

Frequency modulation

Frequency modulation (FM) is a method of impressing data onto an alternating-current (AC) wave by varying the instantaneous frequency of the wave. This scheme can be used with analog or digital data. In analog FM, the frequency of the AC signal wave, also called the carrier, varies in a continuous manner. Thus, there are infinitely many possible carrier frequencies. In narrowband FM, commonly used in two-way wireless communications, the instantaneous carrier frequency varies by up to 5 kilohertz (kHz, where 1 kHz = 1000 hertz or alternating cycles per second) above and below the frequency of the carrier with no modulation. In wideband FM, used in wireless broadcasting, the instantaneous frequency varies by up to several megahertz (MHz, where 1 MHz = 1,000,000 Hz). When the instantaneous input wave has positive polarity, the carrier frequency shifts in one direction; when the instantaneous input wave has negative polarity, the carrier frequency shifts in the opposite direcetion. At every instant in time, the extent of carrier-frequency shift (the deviation) is directly proportional to the extent to which the signal amplitude is positive or negative. In digital FM, the carrier frequency shifts abruptly, rather than varying continuously. The number of possible carrier frequency states is usually a power of 2. If there are only two possible frequency states, the mode is called frequency-shift keying (FSK). In more complex modes, there can be four, eight, or more different frequency states. Each specific carrier frequency represents a specific digital input data state. Frequency modulation is similar in practice to phase modulation (PM). When the instantaneous frequency of a carrier is varied, the instantaneous phase changes as well. The converse also holds: When the instantaneous phase is varied, the instantaneous frequency changes. But FM and PM are not exactly equivalent, especially in analog applications. When an FM receiver is used to demodulate a PM signal, or when an FM signal is intercepted by a receiver designed for PM, the audio is distorted. This is because the relationship between frequency and phase variations is not linear; that is, frequency and phase do not vary in direct proportion.

Power Inverter

A power inverter, or inverter, is an electrical power converter that changes direct current (DC) to alternating current (AC);[1] the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits. Solid-state inverters have no moving parts and are used in a wide range of applications, from small switching power supplies in computers, to large electric utility high-voltage direct current applications that transport bulk power. Inverters are commonly used to supply AC power from DC sources such as solar panels or batteries. The inverter performs the opposite function of a rectifier. The electrical inverter is a high-power electronic oscillator. It is so named because early mechanical AC to DC converters were made to work in reverse, and thus were "inverted", to convert DC to AC. Types Square wave The square wave output has a high harmonic content, not suitable for certain AC loads such as motors or transformers. Square wave units were the pioneers of inverter development. Modified sine wave The output of a modified square wave, quasi square, or modified sine wave inverter is similar to a square wave output except that the output goes to zero volts for a time before switching positive or negative. It is simple and low cost (~$0.10USD/Watt) and is compatible with most electronic devices, except for sensitive or specialized equipment, for example certain laser printers, fluorescent lighting, audio equipment.[2] Most AC motors will run off this power source albeit at a reduction in efficiency of approximately 20%[3] Multilevel A multilevel inverter synthesizes a desired voltage from several levels of direct current voltage as inputs. The advantages of using multilevel topology include reduction of power ratings of power devices and lower cost. There are three topologies - diode clamped inverter, flying capacitor inverter and cascaded inverter. [edit]Pure sine wave A pure sine wave inverter produces a nearly perfect sine wave output (less than 3% total harmonic distortion) that is essentially the same as utility-supplied grid power. Thus it is compatible with all AC electronic devices. This is the type used in grid-tie inverters. Its design is more complex, and costs more per unit power.[4] [edit]Resonant Main article: Resonant inverter Resonant inverters are based on resonant current oscillation. [edit]Grid tie Main article: Grid-tie inverter A grid tie inverter is a sine wave inverter designed to inject electricity into the electric power distribution system. Such inverters must synchronise with the frequency of the grid. They usually contain one or more Maximum power point tracking features to extract the maximum amount of power, and also include safety features. [edit]Synchronous Main article: Synchronous inverter A synchronous inverter connects to a grid and allows routing to or from the grid depending on need. [edit]Stand-alone Main article: Stand-alone inverter A stand-alone inverter is often used to convert direct current produced by renewable energy sources like solar panels or small wind turbines for power to homes and small industries, mostly in remote locations lacking a utility grid. [edit]Solar Main article: Solar inverter A solar inverter can be fed into a commercial electrical grid or used by an off-grid electrical network. Solar inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection. [edit]Solar micro Main article: Solar micro-inverter A solar micro-inverter converts direct current from a single solar panel. Micro-inverters contrast with conventional string or central inverter devices, which are connected to multiple solar panels. [edit]Air conditioner Main article: Air conditioner inverter An air conditioner inverter modulates the frequency of the alternating current to control the speed of the air conditioner motor to achieve continuous adjustment of temperature control. [edit]CCFL Main article: CCFL inverter A CCFL inverter powers a cold cathode fluorescent lamp. [edit]Applications [edit]DC power source utilization Inverter designed to provide 115 VAC from the 12 VDC source provided in an automobile. The unit shown provides up to 1.2 amperes of alternating current, or enough to power two sixty watt light bulbs. An inverter converts the DC electricity from sources such as batteries, solar panels, or fuel cells to AC electricity. The electricity can be at any required voltage; in particular it can operate AC equipment designed for mains operation, or rectified to produce DC at any desired voltage. Micro-inverters convert direct current from individual solar panels into alternating current for the electric grid. They are grid tie designs by default. [edit]Uninterruptible power supplies An uninterruptible power supply (UPS) uses batteries and an inverter to supply AC power when main power is not available. When main power is restored, a rectifier supplies DC power to recharge the batteries. [edit]Induction heating Inverters convert low frequency main AC power to higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power. [edit]HVDC power transmission With HVDC power transmission, AC power is rectified and high voltage DC power is transmitted to another location. At the receiving location, an inverter in a static inverter plant converts the power back to AC. [edit]Variable-frequency drives Main article: variable-frequency drive A variable-frequency drive controls the operating speed of an AC motor by controlling the frequency and voltage of the power supplied to the motor. An inverter provides the controlled power. In most cases, the variable-frequency drive includes a rectifier so that DC power for the inverter can be provided from main AC power. Since an inverter is the key component, variable-frequency drives are sometimes called inverter drives or just inverters. [edit]Electric vehicle drives Adjustable speed motor control inverters are currently used to power the traction motors in some electric and diesel-electric rail vehicles as well as some battery electric vehicles and hybrid electric highway vehicles such as the Toyota Prius, BYD e6 and Fisker Karma. Various improvements in inverter technology are being developed specifically for electric vehicle applications.[5] In vehicles with regenerative braking, the inverter also takes power from the motor (now acting as a generator) and stores it in the batteries. [edit]Air conditioning Main article: Inverter air conditioning An inverter air conditioner uses a variable-frequency drive to control the speed of the motor and thus the compressor. [edit]Electroshock weapons Electroshock weapons and tasers have a DC/AC inverter to generate several hundred V AC out of a small 9 V DC battery. The AC is doubled or quadrupled in a diode/capacitor voltage multiplier followed by an impulstransformer with an output of 2 - 10 kV. The principle is also used in electronic flash and bug zappers. [edit]The general case A transformer allows AC voltage to be stepped up or down to a desired voltage at the same frequency. Inverters, plus rectifiers for DC, can be designed to convert from any voltage, AC or DC, to any other voltage, also AC or DC, at any desired frequency. The output power can never exceed the input power, but efficiencies can be high, with a small proportion of the power dissipated as waste heat. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (December 2009) [edit]Circuit description Top: Simple inverter circuit shown with an electromechanical switch and automatic equivalent auto-switching device implemented with two transistors and split winding auto-transformer in place of the mechanical switch. Square waveform with fundamental sine wave component, 3rd harmonic and 5th harmonic [edit]Basic designs In one simple inverter circuit, DC power is connected to a transformer through the centre tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit. The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar mechanism has been used in door bells, buzzers and tattoo guns. As they became available with adequate power ratings, transistors and various other types of semiconductor switches have been incorporated into inverter circuit designs. Certain ratings, especially for large systems (many kilowatts) use thyristors (SCR). SCRs provide large power handling capability in a semiconductor device, and can readily be controlled over a variable firing range. [edit]Output waveforms The switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power supply. Using Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine waves. The sine wave that has the same frequency as the original waveform is called the fundamental component. The other sine waves, called harmonics, that are included in the series have frequencies that are integral multiples of the fundamental frequency. The quality of the inverter output waveform can be expressed by using the Fourier analysis data to calculate the total harmonic distortion (THD). The total harmonic distortion (THD) is the square root of the sum of the squares of the harmonic voltages divided by the fundamental voltage: The quality of output waveform that is needed from an inverter depends on the characteristics of the connected load. Some loads need a nearly perfect sine wave voltage supply to work properly. Other loads may work quite well with a square wave voltage. [edit]Advanced designs H bridge inverter circuit with transistor switches and antiparallel diodes There are many different power circuit topologies and control strategies used in inverter designs. Different design approaches address various issues that may be more or less important depending on the way that the inverter is intended to be used. The issue of waveform quality can be addressed in many ways. Capacitors and inductors can be used to filter the waveform. If the design includes a transformer, filtering can be applied to the primary or the secondary side of the transformer or to both sides. Low-pass filters are applied to allow the fundamental component of the waveform to pass to the output while limiting the passage of the harmonic components. If the inverter is designed to provide power at a fixed frequency, a resonant filter can be used. For an adjustable frequency inverter, the filter must be tuned to a frequency that is above the maximum fundamental frequency. Since most loads contain inductance, feedback rectifiers or antiparallel diodes are often connected across each semiconductor switch to provide a path for the peak inductive load current when the switch is turned off. The antiparallel diodes are somewhat similar to the freewheeling diodes used in AC/DC converter circuits. waveform signal transitions per period harmonics eliminated harmonics amplified System Description THD 2 - - 2-level square wave ~45%[4] 4 3, 9, 27,... - 3-level "modified square wave" > 23.8%[4] 8 5-level "modified square wave" > 6.5%[4] 10 3, 5, 9, 27 7, 11,... 2-level very slow PWM 12 3, 5, 9, 27 7, 11,... 3-level very slow PWM Fourier analysis reveals that a waveform, like a square wave, that is anti-symmetrical about the 180 degree point contains only odd harmonics, the 3rd, 5th, 7th, etc. Waveforms that have steps of certain widths and heights can attenuate certain lower harmonics at the expense of amplifying higher harmonics. For example, by inserting a zero-voltage step between the positive and negative sections of the square-wave, all of the harmonics that are divisible by three (3rd and 9th, etc.) can be eliminated. That leaves only the 5th, 7th, 11th, 13th etc. The required width of the steps is one third of the period for each of the positive and negative steps and one sixth of the period for each of the zero-voltage steps.[6] Changing the square wave as described above is an example of pulse-width modulation (PWM). Modulating, or regulating the width of a square-wave pulse is often used as a method of regulating or adjusting an inverter's output voltage. When voltage control is not required, a fixed pulse width can be selected to reduce or eliminate selected harmonics. Harmonic elimination techniques are generally applied to the lowest harmonics because filtering is much more practical at high frequencies, where the filter components can be much smaller and less expensive. Multiple pulse-width or carrier based PWM control schemes produce waveforms that are composed of many narrow pulses. The frequency represented by the number of narrow pulses per second is called the switching frequency or carrier frequency. These control schemes are often used in variable-frequency motor control inverters because they allow a wide range of output voltage and frequency adjustment while also improving the quality of the waveform. Multilevel inverters provide another approach to harmonic cancellation. Multilevel inverters provide an output waveform that exhibits multiple steps at several voltage levels. For example, it is possible to produce a more sinusoidal wave by having split-rail direct current inputs at two voltages, or positive and negative inputs with a central ground. By connecting the inverter output terminals in sequence between the positive rail and ground, the positive rail and the negative rail, the ground rail and the negative rail, then both to the ground rail, a stepped waveform is generated at the inverter output. This is an example of a three level inverter: the two voltages and ground.[7] [edit]Three phase inverters 3-phase inverter with wye connected load Three-phase inverters are used for variable-frequency drive applications and for high power applications such as HVDC power transmission. A basic three-phase inverter consists of three single-phase inverter switches each connected to one of the three load terminals. For the most basic control scheme, the operation of the three switches is coordinated so that one switch operates at each 60 degree point of the fundamental output waveform. This creates a line-to-line output waveform that has six steps. The six-step waveform has a zero-voltage step between the positive and negative sections of the square-wave such that the harmonics that are multiples of three are eliminated as described above. When carrier-based PWM techniques are applied to six-step waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd harmonic and its multiples are cancelled. 3-phase inverter switching circuit showing 6-step switching sequence and waveform of voltage between terminals A and C (23-2 states) To construct inverters with higher power ratings, two six-step three-phase inverters can be connected in parallel for a higher current rating or in series for a higher voltage rating. In either case, the output waveforms are phase shifted to obtain a 12-step waveform. If additional inverters are combined, an 18-step inverter is obtained with three inverters etc. Although inverters are usually combined for the purpose of achieving increased voltage or current ratings, the quality of the waveform is improved as well. [edit]History [edit]Early inverters From the late nineteenth century through the middle of the twentieth century, DC-to-AC power conversion was accomplished using rotary converters or motor-generator sets (M-G sets). In the early twentieth century, vacuum tubes and gas filled tubes began to be used as switches in inverter circuits. The most widely used type of tube was the thyratron. The origins of electromechanical inverters explain the source of the term inverter. Early AC-to-DC converters used an induction or synchronous AC motor direct-connected to a generator (dynamo) so that the generator's commutator reversed its connections at exactly the right moments to produce DC. A later development is the synchronous converter, in which the motor and generator windings are combined into one armature, with slip rings at one end and a commutator at the other and only one field frame. The result with either is AC-in, DC-out. With an M-G set, the DC can be considered to be separately generated from the AC; with a synchronous converter, in a certain sense it can be considered to be "mechanically rectified AC". Given the right auxiliary and control equipment, an M-G set or rotary converter can be "run backwards", converting DC to AC. Hence an inverter is an inverted converter.[8][9] [edit]Controlled rectifier inverters Since early transistors were not available with sufficient voltage and current ratings for most inverter applications, it was the 1957 introduction of the thyristor or silicon-controlled rectifier (SCR) that initiated the transition to solid state inverter circuits. 12-pulse line-commutated inverter circuit The commutation requirements of SCRs are a key consideration in SCR circuit designs. SCRs do not turn off or commutate automatically when the gate control signal is shut off. They only turn off when the forward current is reduced to below the minimum holding current, which varies with each kind of SCR, through some external process. For SCRs connected to an AC power source, commutation occurs naturally every time the polarity of the source voltage reverses. SCRs connected to a DC power source usually require a means of forced commutation that forces the current to zero when commutation is required. The least complicated SCR circuits employ natural commutation rather than forced commutation. With the addition of forced commutation circuits, SCRs have been used in the types of inverter circuits described above. In applications where inverters transfer power from a DC power source to an AC power source, it is possible to use AC-to-DC controlled rectifier circuits operating in the inversion mode. In the inversion mode, a controlled rectifier circuit operates as a line commutated inverter. This type of operation can be used in HVDC power transmission systems and in regenerative braking operation of motor control systems. Another type of SCR inverter circuit is the current source input (CSI) inverter. A CSI inverter is the dual of a six-step voltage source inverter. With a current source inverter, the DC power supply is configured as a current source rather than a voltage source. The inverter SCRs are switched in a six-step sequence to direct the current to a three-phase AC load as a stepped current waveform. CSI inverter commutation methods include load commutation and parallel capacitor commutation. With both methods, the input current regulation assists the commutation. With load commutation, the load is a synchronous motor operated at a leading power factor. As they have become available in higher voltage and current ratings, semiconductors such as transistors or IGBTs that can be turned off by means of control signals have become the preferred switching components for use in inverter circuits. [edit]Rectifier and inverter pulse numbers Rectifier circuits are often classified by the number of current pulses that flow to the DC side of the rectifier per cycle of AC input voltage. A single-phase half-wave rectifier is a one-pulse circuit and a single-phase full-wave rectifier is a two-pulse circuit. A three-phase half-wave rectifier is a three-pulse circuit and a three-phase full-wave rectifier is a six-pulse circuit. [10] With three-phase rectifiers, two or more rectifiers are sometimes connected in series or parallel to obtain higher voltage or current ratings. The rectifier inputs are supplied from special transformers that provide phase shifted outputs. This has the effect of phase multiplication. Six phases are obtained from two transformers, twelve phases from three transformers and so on. The associated rectifier circuits are 12-pulse rectifiers, 18-pulse rectifiers and so on... When controlled rectifier circuits are operated in the inversion mode, they would be classified by pulse number also. Rectifier circuits that have a higher pulse number have reduced harmonic content in the AC input current and reduced ripple in the DC output voltage. In the inversion mode, circuits that have a higher pulse number have lower harmonic content in the AC output voltage waveform. [edit]See also