A grid-leak detector is a combination diode rectifier and audio amplifier used as a detector in vacuum tube A.M. radio receivers. In the circuit, the grid of the detector -- usually a low-mu or medium-mu triode -- is connected to the secondary of the final R.F. or I.F. transformer through a capacitor (100 µµF to 330 µµF -- 250 µµF being typical). This capacitor eliminates R.F. in the output circuit. (An R.F. choke in the plate circuit may also be used to eliminate any transient R.F. in the output circuit.) The grid is negatively biased through a grid leak resistor (1 to 5 megohms -- 2.2 megohms being typical). This resistor may be parallel connected with the grid capacitor, or it may be connected directly to ground. As D.C. current flows through the grid leak resistor, the control grid functions like the plate of a diode, which causes rectifying action to occur. Frequency variations in voltage across the bias resistor are amplified through the tube as in a normal audio amplifier.
A grid-leak detector has considerably greater sensitivity than a diode. The sensitivity is further increased by using a tetrode or pentode with a sharp cut-off control grid instead of a triode. The operation is equivalent to that of the triode circuit except controlled feedback is applied and controlled by adjustment of the screen-grid voltage.
All grid-leak detectors require a plate by-pass capacitor connected to ground to regulate plate current. For triodes, this capacitor should have a value of 0.001 µF to 0.002 µF. For tetrodes and pentodes, this capacitor should have a value of 250 µµF to 500 µµF. Tetrodes and pentodes grid-leak detectors also require a screen grid by-pass capacitor of at least 0.47 µF.
The heyday for grid-leak detectors was the 1920s when battery-operated, multi-dial T.R.F. radios using low-mu triodes with directly heated cathodes was the norm. When indirectly heated cathodes and A.C. powered receivers were introduced in 1927, most manufacturers switched to plate detectors, and later to diode detectors.
Although the regenerative grid-leak detector was one of the more sensitive detectors of its day, its many disadvantages limited it for use only in the simplest receivers. However, this did not stop some manufacturers from using regenerative detectors in their radios. Many of the cathedral radios and other table models made by Philco during the early 1930s used a regenerative detector fed by a superheterodyne converter tube. This allowed the detector to double as a sort of I.F. amplifier, thus saving money by eliminating the need for another tube.
2009年1月22日星期四
Grid bias
Grid bias is a DC voltage applied to electron tubes (or valves in British English) with three electrodes or more, such as triodes. The control grid (usually the first grid) of these devices is used to control the electron flow from the heated cathode to the positively charged anode. Bias point in small-signal applications is set to minimize distortion and achieve sufficiently low power draw. In high-power applications, biasing is typically set for maximum available output power or voltage, with a secondary target of either low distortion or high efficiency.
In a typical voltage amplifier, including power stages of most audio power amplifiers, DC bias voltage is negative relative to cathode potential. Instant grid voltage (sum of DC bias and AC input signal) should never rise above cathode potential to prevent grid-to-cathode currents that overload preceding amplifier stages and may cause severe even-order distortion. High transconductance tubes develop significant grid currents even with small negative bias; in these cases, maximum instant voltage ceiling is lowered to -1.0..-0.5 Volt.
High efficiency Class B+ push-pull amplifiers operate at higher bias points (near zero or even positive values). These designs take care of grid currents through the use of cathode followers or interstage transformers easing current load on the driver stages, and deep negative feedback to minimize distortion.
High power transmitter tubes (oscillators and modulators) are frequently positively biased to maximize radio frequency output. Distortion is minimized by using band-pass filter loads tuned to the desired radio frequency.
Bias voltage is obtained through:
An external voltage source (fixed bias) - a battery or a dedicated DC power supply. When the cathode potential is raised above ground (as in cascode circuits), bias voltage is obtained by tapping into main (positive) plate power supply.
Automatic bias - using a cathode resistor to raise cathode potential above grid (tied to ground) and stabilize plate current;
Grid leak bias - diverting DC grid current through a high value grid resistor.
In a typical voltage amplifier, including power stages of most audio power amplifiers, DC bias voltage is negative relative to cathode potential. Instant grid voltage (sum of DC bias and AC input signal) should never rise above cathode potential to prevent grid-to-cathode currents that overload preceding amplifier stages and may cause severe even-order distortion. High transconductance tubes develop significant grid currents even with small negative bias; in these cases, maximum instant voltage ceiling is lowered to -1.0..-0.5 Volt.
High efficiency Class B+ push-pull amplifiers operate at higher bias points (near zero or even positive values). These designs take care of grid currents through the use of cathode followers or interstage transformers easing current load on the driver stages, and deep negative feedback to minimize distortion.
High power transmitter tubes (oscillators and modulators) are frequently positively biased to maximize radio frequency output. Distortion is minimized by using band-pass filter loads tuned to the desired radio frequency.
Bias voltage is obtained through:
An external voltage source (fixed bias) - a battery or a dedicated DC power supply. When the cathode potential is raised above ground (as in cascode circuits), bias voltage is obtained by tapping into main (positive) plate power supply.
Automatic bias - using a cathode resistor to raise cathode potential above grid (tied to ground) and stabilize plate current;
Grid leak bias - diverting DC grid current through a high value grid resistor.
Alternator synchronization
The process of connecting an AC generator (alternator) to other AC generators is known as synchronization and is crucial for the generation of AC electrical power.
Operation Modes of Alternator
An alternator is an AC generator used mostly at power stations. The alternator is technically known as a synchronous generator. There are two modes of its operation:
Stand-alone operation: The alternator is operated isolated or connected to a DC supply via a rectifier. There is no need for synchronization in a stand-alone operation. An isolated example is a diesel engine-driven alternator used as a standby generator. An automotive alternator is used to recharge the battery with the aid of a three-phase diode rectifier.
Parallel operation: The alternator is connected with other alternators. This mode of operation takes place at power stations where many generators run in parallel. The generators are connected together via transformers and busbars and so a power network or grid is formed. The power grid is like a water pool and the generators are like pipes that supply the pool with water. The water is analogous to energy. The power grid is sometimes referred to as a power pool. The grid is also referred to as infinite busbar as far as synchronization is concerned. However, the infinite bus implies fixed voltage, frequency, phase sequence and phase angle. The grid is composed of different voltages and frequencies. Hence, it is technically said that an alternator is synchronized with the infinite bus.
Conditions
There are five conditions that must be met before the synchronization process takes place. The alternator must have equal line voltage, frequency, phase sequence , phase angle and waveform to that of the infinite bus.
In the past, synchronization was performed manually using three-lamp method. Nowadays, the process is automatically operated and controlled with the aid of synch relays and micro-electronic systems.
Operation Modes of Alternator
An alternator is an AC generator used mostly at power stations. The alternator is technically known as a synchronous generator. There are two modes of its operation:
Stand-alone operation: The alternator is operated isolated or connected to a DC supply via a rectifier. There is no need for synchronization in a stand-alone operation. An isolated example is a diesel engine-driven alternator used as a standby generator. An automotive alternator is used to recharge the battery with the aid of a three-phase diode rectifier.
Parallel operation: The alternator is connected with other alternators. This mode of operation takes place at power stations where many generators run in parallel. The generators are connected together via transformers and busbars and so a power network or grid is formed. The power grid is like a water pool and the generators are like pipes that supply the pool with water. The water is analogous to energy. The power grid is sometimes referred to as a power pool. The grid is also referred to as infinite busbar as far as synchronization is concerned. However, the infinite bus implies fixed voltage, frequency, phase sequence and phase angle. The grid is composed of different voltages and frequencies. Hence, it is technically said that an alternator is synchronized with the infinite bus.
Conditions
There are five conditions that must be met before the synchronization process takes place. The alternator must have equal line voltage, frequency, phase sequence , phase angle and waveform to that of the infinite bus.
In the past, synchronization was performed manually using three-lamp method. Nowadays, the process is automatically operated and controlled with the aid of synch relays and micro-electronic systems.
Indian locomotive class WAP-4
WAP-4 is one of the most important electric locomotives used in India. It is a highly powerful class capable of hauling 26 coaches at the speed of 160 km/h. It is also among the most widely used locomotive.
The locomotive was developed, after a previous class WAP-1 was found inadequate to haul the longer, heavier express trains that were becoming the mainstay of the Indian Railways network. It was introduced in 1994, with a similar bodyshell to the WAP-1 class, but with Hitachi traction motors developing 5000hp (5350 hp starting).
Electricals are traditional DC loco type tap changers, driving 6 traction motors arranged in Bo-Bo fashion. This locomotive has proved to be highly successful, with over 450 units in service and more being produced. Newer examples have been fitted with Microprocessor Controlled diagnostics, Static Convertor units (instead of arnos) and roof mounted Dynamic (Rheostatic) Brakes.
The locomotive can be seen in service across the electrified network of Indian Railways and is homed at 11 sheds (depots).
Design
The loco has a streamlined twin cab carbody design, with top-mounted headlamps. The first 150 or so units had the headlamp mounted at waist level, with the lights being mounted in a protruding nacelle. Later on the headlamps were placed in a recessed nacelle, and from road # 22579 onward, the headlamps were moved to the top. Newer locos also feature larger windshields, more spacious driver cabin with bucket type seats and ergonomic controls. The control panel also features a mix of digital and analog displays in newer units (all analog display in older versions).
The loco features higher power rated silicon rectifiers and indigenously-designed 5400kVA transformer coupled with Hitachi HS15250 traction motors. Starting power is 5,350 hp (3,990 kW), with 5,000 hp (3,700 kW) being supplied continuously.
Original units were weighed 120 tonnes, which was brought down to 112 tonnes through the usage of lighter material.
Some WAP-1 and WAP-6 units were rebuilt to WAP-4 specifications after replacing the bogies & electricals.
Performance
The WAP-4 class hauls 24 coach (1430 tonne) trains at 110 km/h. It is also used to haul the premier Rajdhani & Shatabdi Expresses at 130 km/h. In trials, the loco has achieved a top speed of 169.5 km/h, though Indian Railways limits its top speed to 140 km/h.
With a 24 coach passenger train, the acceleration time / distances are:
110 km/h - 338 seconds (6.8km)
120 km/h - 455 seconds (10.5km)
130 km/h - 741 seconds (20.5 km)
Starting Tractive Effort (Te) - 30800 kg/force
Polyphase system
A polyphase system is a means of distributing alternating current electrical power. Polyphase systems have three or more energized electrical conductors carrying alternating currents with a definite time offset between the voltage waves in each conductor. Polyphase systems are particularly useful for transmitting power to electric motors. The most common example is the three-phase power system used for most industrial applications.
Phases
Main articles: Phase and Phase shifting
In the very early days of commercial electric power, some installations used two phase four-wire systems for motors. The chief advantage of these was that the winding configuration was the same as for a single-phase capacitor-start motor, and, by using a four-wire system, conceptually the phases were independent and easy to analyze with mathematical tools available at the time. Two-phase systems have been replaced with three-phase systems. A two-phase supply with 90 degrees between phases can be derived from a three-phase system using a Scott-connected transformer.
A polyphase system must provide a defined direction of phase rotation, so mirror image voltages do not count towards the phase order. A 3-wire system with two phase conductors 180 degrees apart is still only single phase. Such systems are sometimes described as split phase.
Motors
Polyphase power is particularly useful in AC motors, such as the induction motor, where it generates a rotating magnetic field. When a three-phase supply completes one full cycle, the magnetic field of a two-pole motor has rotated through 360° in physical space; motors with more pairs of poles require more power supply cycles to complete one physical revolution of the magnetic field, and so these motors run slower. Nikola Tesla and Michail Dolivo-Dobrovolsky invented the first practical induction motors using a rotating magnetic field - previously all commercial motors were DC, with expensive commutators, high-maintenance brushes, and characteristics unsuitable for operation on an alternating current network. Polyphase motors are simple to construct, are self-starting, and have little vibration compared with single-phase motors.
Higher phase order
Higher phase numbers than three have been used. A common practice for rectifier installations and in HVDC converters is to provide six phases, with 60 degree phase spacing, to reduce harmonic generation in the AC supply system and to provide smoother direct current. Experimental high-phase-order transmission lines have been built with up to 12 phases. These allow application of Extra High Voltage (EHV) design rules at lower voltages, and would permit increased power transfer in the same transmission line corridor width.
Phases
Main articles: Phase and Phase shifting
In the very early days of commercial electric power, some installations used two phase four-wire systems for motors. The chief advantage of these was that the winding configuration was the same as for a single-phase capacitor-start motor, and, by using a four-wire system, conceptually the phases were independent and easy to analyze with mathematical tools available at the time. Two-phase systems have been replaced with three-phase systems. A two-phase supply with 90 degrees between phases can be derived from a three-phase system using a Scott-connected transformer.
A polyphase system must provide a defined direction of phase rotation, so mirror image voltages do not count towards the phase order. A 3-wire system with two phase conductors 180 degrees apart is still only single phase. Such systems are sometimes described as split phase.
Motors
Polyphase power is particularly useful in AC motors, such as the induction motor, where it generates a rotating magnetic field. When a three-phase supply completes one full cycle, the magnetic field of a two-pole motor has rotated through 360° in physical space; motors with more pairs of poles require more power supply cycles to complete one physical revolution of the magnetic field, and so these motors run slower. Nikola Tesla and Michail Dolivo-Dobrovolsky invented the first practical induction motors using a rotating magnetic field - previously all commercial motors were DC, with expensive commutators, high-maintenance brushes, and characteristics unsuitable for operation on an alternating current network. Polyphase motors are simple to construct, are self-starting, and have little vibration compared with single-phase motors.
Higher phase order
Higher phase numbers than three have been used. A common practice for rectifier installations and in HVDC converters is to provide six phases, with 60 degree phase spacing, to reduce harmonic generation in the AC supply system and to provide smoother direct current. Experimental high-phase-order transmission lines have been built with up to 12 phases. These allow application of Extra High Voltage (EHV) design rules at lower voltages, and would permit increased power transfer in the same transmission line corridor width.
Reservoir capacitor
A reservoir capacitor is a capacitor that is used to smooth the pulsating DC from an AC rectifier.
Performance with low impedance source
The above diagram shows reservoir performance from a near zero impedance source, such as a mains supply. As the rectifier voltage increases, it charges the capacitor and also supplies current to the load. At the end of the quarter cycle, the capacitor is charged to its peak value Vm of the rectifier voltage. Following this, the rectifier voltage starts to decrease as it enters the next quarter cycle. This initiates the discharge of the capacitor through the load.
Performance with significant impedance source
These circuits are very frequently fed from transformers, and have significant resistance. Transformer resistance modifies the reservoir capacitor waveform, changes the peak voltage, and introduces regulation issues.
Performance with low impedance source
The above diagram shows reservoir performance from a near zero impedance source, such as a mains supply. As the rectifier voltage increases, it charges the capacitor and also supplies current to the load. At the end of the quarter cycle, the capacitor is charged to its peak value Vm of the rectifier voltage. Following this, the rectifier voltage starts to decrease as it enters the next quarter cycle. This initiates the discharge of the capacitor through the load.
Performance with significant impedance source
These circuits are very frequently fed from transformers, and have significant resistance. Transformer resistance modifies the reservoir capacitor waveform, changes the peak voltage, and introduces regulation issues.
Electra the Electric Train
Electra the Electric Engine is a fictional character from the rock musical Starlight Express.
Electra is the newest train to enter the yard and, therefore, Control's newest toy. He comes with his own line of components that are loyal to him. He's rich, self-centered and sexy. His eyes are set on Pearl and they race in the heats until she chooses Greaseball. Electra then takes Dinah for the uphill Final after Greaseball dumps her. Dissatisfied with his performance, Dinah disconnects herself from him and he calls for CB to race with him for the re-run Final. In the end, he crashes along with Greaseball and CB.
Character
Electra is, from the moment he enters, seen as some sort of Prima Donna. Even before then, as we meet his components, we aretold he is a "megastar" and "rich, and cool". He also seems to think a lot of himself, and the subtext in his song (along with choreography and his character tick-overs) suggests he is AC/DC.
Inspiration
Electra's character is influenced by David Bowie, an androgynous Rock Star. He, along with Greaseball the Diesel, are the Ugly stepsisters in the original concept of the show being Cinderella for trains. He also reminds some of the Rum Tum Tugger from the musical Cats because both are vain, sexy and rebellious.
Musical numbers
Electra sings "AC/DC", his opening theme and also features in group numbers. In the Original London version he has a second solo "No Comeback", which he sings as he leaves in a rage after losing the Race final to Rusty. This song did not appear in any subsequent productions. He now sings "One Rock 'n' Roll Too Many" with Greaseball and Caboose.
Costume
Electra's costume is based on a palatte of electric blue, silver and red. He is patterned to resemble computer circuitry. His impressive mohawk is usually styled to resemble frayed wire, but when played by John Partridge his head was shaved and painted. His look bears a passing resemblance to other mechanoids, Transformers. As one of the most eye-catching designs, Electra is often used for advertising the show.
Electra's Components are designed to represent elements of a Superstar's entourage. Krupp is the Chauffeur and Bodyguard, represented in his uniformed hat, sunshades and gun holster. Wrench, as a mechanic, wears a welding apron and her hat represents the crane found on repair trucks. Purse wears pinstripes as suits an accountant. Joule's London design reflected her Animal Truck origin, her skintight red/grey costume and white bib resembling Bombalurina from the musical Cats. Volta wears elegant black, her hair styled into a fan, reflecting her nature of a Freezer Truck. All the component's costumes are designed on a restricted colour palatte of Red, Electric Blue, Silver/Grey and Black, this reinforces their relationship to Electra onstage.
In Starlight on Ice, Electra and the components' outfits change. Instead of being colorful, Electra is now bright "warning sign" yellow with a matching mohawk. His look is much sleeker and bears no resemblance to the original design. The components wear very similar outfits which are yellow and silver.
Electra's make-up
Electra's make-up is an assortment of blue, silver and red glittered stripes, patterns and lipstick, as well as a pair of long, silver eyelashes.In the London production, his look was less camp, and he had a black and white checkered pattern on one side of his face.
Solid state relay
A solid state relay (SSR) is an electronic switch, which, unlike an electromechanical relay, contains no moving parts. The types of SSR are photo-coupled SSR, transformer-coupled SSR, and hybrid SSR. A photo-coupled SSR is controlled by a low voltage signal which is isolated optically from the load. The control signal in a photo-coupled SSR typically energizes an LED which activates a photo-sensitive diode. The diode turns on a back-to-back thyristor, silicon controlled rectifier, or MOSFET transistor to switch the load.
Operation
Voltage applied to the control line of an SSR causes the LED to shine on the photo-sensitive diode. This produces a voltage between the MOSFET source and its gate, causing the MOSFET to turn on. An SSR based on a single MOSFET, or multiple MOSFETs in a paralleled array works well for DC loads.
There is an inherent substrate diode in all MOSFETs that conducts in the reverse direction. This means that a single MOSFET can't block current in both directions. For AC (bi-directional) operation, two MOSFETs are arranged back to back with their source pins tied together. Their drain pins are connected to either side of the output. The substrate diodes then are alternately reverse biased in order to block current when the relay is off. When the relay is on, the common source is always riding on the instantaneous signal level and both gates are biased positive relative to the source by the photo-diode.
It is common to provide access to the common source so that multiple MOSFETs can be wired in parallel if switching a DC load. There is also commonly some circuitry to discharge the gate when the LED is turned off, speeding the relay's turn-off.
Advantages over mechanical relays
SSRs are faster than electromechanical relays; their switching time is dependent on the time needed to power the LED on and off, typically on the order of nanoseconds
Increased lifetime due to the fact that there are no moving parts, and thus no wear
Clean, bounceless operation
Decreased electrical noise when switching
Can be used in explosive environments where a spark must not be generated during turn-on
Totally silent operation
Smaller than a corresponding mechanical relay.
Disadvantages
Fail short more easily than electro-mechanical relays
Increased electrical noise when conducting
Higher impedance when closed (-> heat production)
Lower impedance when open
Reverse leakage current when open (µA range)
Possibility of false switching due to voltage transients
Often more expensive than comparable electromechanical relays
Operation
Voltage applied to the control line of an SSR causes the LED to shine on the photo-sensitive diode. This produces a voltage between the MOSFET source and its gate, causing the MOSFET to turn on. An SSR based on a single MOSFET, or multiple MOSFETs in a paralleled array works well for DC loads.
There is an inherent substrate diode in all MOSFETs that conducts in the reverse direction. This means that a single MOSFET can't block current in both directions. For AC (bi-directional) operation, two MOSFETs are arranged back to back with their source pins tied together. Their drain pins are connected to either side of the output. The substrate diodes then are alternately reverse biased in order to block current when the relay is off. When the relay is on, the common source is always riding on the instantaneous signal level and both gates are biased positive relative to the source by the photo-diode.
It is common to provide access to the common source so that multiple MOSFETs can be wired in parallel if switching a DC load. There is also commonly some circuitry to discharge the gate when the LED is turned off, speeding the relay's turn-off.
Advantages over mechanical relays
SSRs are faster than electromechanical relays; their switching time is dependent on the time needed to power the LED on and off, typically on the order of nanoseconds
Increased lifetime due to the fact that there are no moving parts, and thus no wear
Clean, bounceless operation
Decreased electrical noise when switching
Can be used in explosive environments where a spark must not be generated during turn-on
Totally silent operation
Smaller than a corresponding mechanical relay.
Disadvantages
Fail short more easily than electro-mechanical relays
Increased electrical noise when conducting
Higher impedance when closed (-> heat production)
Lower impedance when open
Reverse leakage current when open (µA range)
Possibility of false switching due to voltage transients
Often more expensive than comparable electromechanical relays
MagSafe
The MagSafe connector is a power connector introduced in conjunction with the MacBook Pro at the Macworld Expo in San Francisco on January 10, 2006. The MagSafe connector is held in place magnetically. As a result, if it is tugged on—for instance, by someone tripping over the cord—it comes out of the socket safely, without damaging it or the computer or pulling the computer off its table or desk. MagSafe is similar to the magnetic power connectors that many deep fryers and Japanese countertop cooking appliances have in order to avoid spilling their dangerously hot contents.
Features
The MagSafe connector pins are designed so that the rectangular connector can be inserted in either orientation. LEDs on both sides show green if the computer batteries are fully charged and amber if they are charging. MagSafe can be found on MacBook Pro, MacBook and MacBook Air notebook computers.
Though the 60 W MacBook and 85 W MacBook Pro MagSafe connectors are identical, Apple recommends using only the adapter provided with the machine. The MacBook Air has a smaller 45 W version of the MagSafe adapter.
Apple's MagSafe Airline Adapter is available for DC hookups on certain airplanes.
Pinout
The MagSafe connector pins are palindromic. The first and second pin on each side of the tiny central pin has continuity with its mirror pin.
The inner large pin is V+ @ 16.5 VDC. Measuring with no load will give 6.86 VDC; the full 16.5 V is provided to the proper load.
The outer large pin is ground
The tiny center pin appears to be charge control pin to change LED color and possibly adapter switch off
The rectangular metal shroud has no electrical function. Its purpose is solely for shielding the electrical pins and acting as a ferrous attractor for the magnets within the laptop's power receptacle.
Criticisms and defects
Apple has not licensed third-party products using MagSafe, however manufacturers have devised a workaround: their MagSafe items use the actual connector from Apple’s AC adapter, grafted onto their own product. Since this uses an actual Apple product, purchased legally, no licensing agreements are violated.
Some users keep reporting (as of April 16 2008) problems with the quality of the construction of the MagSafe cords, giving the product low marks on the Apple Store’s website. Common complaints include plug separating from the cord (fraying), transformer shorting, and pin springs losing elasticity.
Plate detector (radio)
A plate detector is a vacuum tube detector circuit used in A.M. radios. This circuit employs a tube with an indirectly heated cathode, typically a medium-mu triode, or a tetrode or pentode with a sharp cut-off control grid. Rectification of R.F. signals occurs in the plate of the detector tube. This differs from a grid-leak detector, which achieves rectification in the control grid. It also differs from the diode detector circuit commonly used to provide both R.F. rectification and automatic volume control (A.V.C.) bias to the R.F. amplifier tubes.
Overview
Plate detectors are used in both T.R.F. and superheterodyne receivers. The grid is connected directly to the secondary of the final R.F. or I.F. transformer. The cathode is connected to ground through a circuit consisting of a parallel-connected bias resistor (usually 10 KΩ to 50 KΩ) and bypass capacitor (usually 0.25 µF to 0.5 µF). When sufficient negative bias is applied to the grid, the plate current is pushed almost to the cut-off point. When a modulated R.F. signal is applied to the grid under these conditions, a corresponding increase in plate current occurs. As the signal amplitude varies, the plate current also varies, causing the plate to act as a diode detector while the tube as a whole also acts as an audio amplifier. A plate bypass capacitor (usually 500 µµF to 0.002 µF for triodes, or 250 µµF to 0.001 µF for tetrodes and pentodes) is used to regulate plate current.
Like most A.F. amplifiers in radios, the plate voltage is usually less than 60 volts. When a tetrode or pentode is used, the screen grid voltage is usually about one-half the plate voltage.
Plate detector circuits were commonly used from the introduction of indirectly heated cathode tubes in the late 1920s until the start of World War II. As R.F. tubes became more sensitive, grid-leak detectors (which are more sensitive than plate detectors) became less practical. Diode detectors were popular because, unlike plate detector circuits, they could also provide A.V.C. bias. However, the dual-diode/triode and dual-diode/pentode tubes commonly used in these circuits had bulk wholesale costs that were as much as twice the cost of the tubes commonly used as plate detectors. This made plate detector circuits more practical for low-priced radios sold during the depths of the Great Depression.
Because an indirectly heated cathode is required for this circuit to operate, it is not used in battery-operated radios.
Controlling volume levels
Plate detector circuits usually lack an A.V.C. bias circuit. In receivers equipped with A.V.C., volume levels are adjusted by a potentiometer (typically 500 KΩ to 2 megohms audio taper) that controls audio signal levels at the control grid of the A.F. amplifier. In receivers not equipped with A.V.C., the most common connection of the volume control potentiometer (typically 4 KΩ to 15 KΩ linear taper) is as follows:
The low side of the potentiometer is connected to the antenna connection at the antenna input coil;
The center wiper is connected to ground (in A.C. receivers) or B- (in A.C./D.C. receivers);
The high side is connected to the cathode of at least one R.F. amplifier (in T.R.F. receivers) or to the converter and/or the I.F. amplifier (in superheterodyne receivers).
To assure that proper cathode bias is maintained, many non-A.V.C. volume controls are usually equipped with a "stop" that maintains a small amount of resistance between the center wiper and the high end connection.
Other volume control circuits in non-A.V.C. receivers include:
A potentiometer (typically 500 KΩ audio taper) where the high end and center wiper are connected as above, but where the low end is connected to the control grid of audio output tube. (In this circuit, the potentiometer replaces the bias resistor for the output tube's control grid);
A linear taper potentiometer that adjusts the screen grid voltages of the set's R.F. amplifiers (if they are tetrodes or pentodes);
A linear taper potentiometer connected to the antenna (high end), ground (low end) and the antenna input coil (center wiper).
Because the volume control in non-A.V.C. receivers adjusts R.F. signal levels rather than A.F. signal levels, the volume control must be manipulated while tuning the radio in order to find weak signals.
Tubes commonly used as plate detectors
6C6
6J7
6SJ7
12F5
12J5
12J7
12SF5
12SJ7
24 and 24-A
27
36
37
56
57
76
77
Overview
Plate detectors are used in both T.R.F. and superheterodyne receivers. The grid is connected directly to the secondary of the final R.F. or I.F. transformer. The cathode is connected to ground through a circuit consisting of a parallel-connected bias resistor (usually 10 KΩ to 50 KΩ) and bypass capacitor (usually 0.25 µF to 0.5 µF). When sufficient negative bias is applied to the grid, the plate current is pushed almost to the cut-off point. When a modulated R.F. signal is applied to the grid under these conditions, a corresponding increase in plate current occurs. As the signal amplitude varies, the plate current also varies, causing the plate to act as a diode detector while the tube as a whole also acts as an audio amplifier. A plate bypass capacitor (usually 500 µµF to 0.002 µF for triodes, or 250 µµF to 0.001 µF for tetrodes and pentodes) is used to regulate plate current.
Like most A.F. amplifiers in radios, the plate voltage is usually less than 60 volts. When a tetrode or pentode is used, the screen grid voltage is usually about one-half the plate voltage.
Plate detector circuits were commonly used from the introduction of indirectly heated cathode tubes in the late 1920s until the start of World War II. As R.F. tubes became more sensitive, grid-leak detectors (which are more sensitive than plate detectors) became less practical. Diode detectors were popular because, unlike plate detector circuits, they could also provide A.V.C. bias. However, the dual-diode/triode and dual-diode/pentode tubes commonly used in these circuits had bulk wholesale costs that were as much as twice the cost of the tubes commonly used as plate detectors. This made plate detector circuits more practical for low-priced radios sold during the depths of the Great Depression.
Because an indirectly heated cathode is required for this circuit to operate, it is not used in battery-operated radios.
Controlling volume levels
Plate detector circuits usually lack an A.V.C. bias circuit. In receivers equipped with A.V.C., volume levels are adjusted by a potentiometer (typically 500 KΩ to 2 megohms audio taper) that controls audio signal levels at the control grid of the A.F. amplifier. In receivers not equipped with A.V.C., the most common connection of the volume control potentiometer (typically 4 KΩ to 15 KΩ linear taper) is as follows:
The low side of the potentiometer is connected to the antenna connection at the antenna input coil;
The center wiper is connected to ground (in A.C. receivers) or B- (in A.C./D.C. receivers);
The high side is connected to the cathode of at least one R.F. amplifier (in T.R.F. receivers) or to the converter and/or the I.F. amplifier (in superheterodyne receivers).
To assure that proper cathode bias is maintained, many non-A.V.C. volume controls are usually equipped with a "stop" that maintains a small amount of resistance between the center wiper and the high end connection.
Other volume control circuits in non-A.V.C. receivers include:
A potentiometer (typically 500 KΩ audio taper) where the high end and center wiper are connected as above, but where the low end is connected to the control grid of audio output tube. (In this circuit, the potentiometer replaces the bias resistor for the output tube's control grid);
A linear taper potentiometer that adjusts the screen grid voltages of the set's R.F. amplifiers (if they are tetrodes or pentodes);
A linear taper potentiometer connected to the antenna (high end), ground (low end) and the antenna input coil (center wiper).
Because the volume control in non-A.V.C. receivers adjusts R.F. signal levels rather than A.F. signal levels, the volume control must be manipulated while tuning the radio in order to find weak signals.
Tubes commonly used as plate detectors
6C6
6J7
6SJ7
12F5
12J5
12J7
12SF5
12SJ7
24 and 24-A
27
36
37
56
57
76
77
Brent Fitz
Brent Fitz is a Canadian-born musician and recording artist known best for his stints as the drummer for Union, Lamya, Vince Neil, Theory of a Deadman, Streetheart, Harlequin, Econoline Crush, Indigenous and Alice Cooper.
Biography
Fitz is a native of Winnipeg, Manitoba, Canada where he attended and graduated from John Taylor Collegiate in 1988. After leaving Winnipeg in the 90's he lived for some time in Los Angeles, California and currently resides in Las Vegas, Nevada.
Brent started drums at a very young age and played heavily in his middle school and high school music programs. Brent received lots of theory training as a child/teen with the Royal Conservatory of Music (Toronto) and is a skilled piano player as well as a guitar player and back-up vocalist.
Brent got his start playing in various Winnipeg clubs and outlying areas in a cover band named New Alliance. He later moved on to join the heavier Winnipeg based touring club act Seventh Heaven which evolved into Shake Naked.Schedules with Seventh Heaven and Shake Naked were much more extensive and involved touring most of Canada. Connections to the city of Los Angeles within the band Seventh Heaven allowed Brent to have the opportunity to seek work in that market as a performer and session player.
Working with previous Shake Naked vocalist Lenita Erickson later proved fruitful as Lenita's friend Bruce Kulick of Kiss fame invited Brent to join him in a recording effort after hearing him play. That band would become known as Union and would also include John Corabi on vocals formerly of The Scream and Mötley Crüe, Jamie Hunting of David Lee Roth on bass, as well as Bruce on guitar. Brent briefly played in Bulletboys in 2000 , as well as recorded and toured with Gilby Clarke of Guns 'N Roses fame.
Brent would later receive an invitation to tour with Vince Neil's solo act as drummer and keyboardist.[ Performing on several international tours, Brent appeared in a live performance with Vince on VH1's TV show "Remaking: Vince Neil" in 2004.
After leaving the Vince Neil team Brent hooked up with Theory of a Deadman as their touring drummer. Brent appeared in four music videos with the band, as well as made several TV appearances including The Tonight Show With Jay Leno.. Brent played piano and sang with the band for several acoustic performances as well.
Brent has since been performing with Alice Cooper while drummer Eric Singer does some dates with Kiss, as well performing with Harlequin, and Indigenous . As of August 2007, Brent has announced his joining of Canadian rock act Econoline Crush. Although Brent is officially in Econoline Crush, he remains a backup drummer with Alice Cooper and infrequently tours with him.
Biography
Fitz is a native of Winnipeg, Manitoba, Canada where he attended and graduated from John Taylor Collegiate in 1988. After leaving Winnipeg in the 90's he lived for some time in Los Angeles, California and currently resides in Las Vegas, Nevada.
Brent started drums at a very young age and played heavily in his middle school and high school music programs. Brent received lots of theory training as a child/teen with the Royal Conservatory of Music (Toronto) and is a skilled piano player as well as a guitar player and back-up vocalist.
Brent got his start playing in various Winnipeg clubs and outlying areas in a cover band named New Alliance. He later moved on to join the heavier Winnipeg based touring club act Seventh Heaven which evolved into Shake Naked.Schedules with Seventh Heaven and Shake Naked were much more extensive and involved touring most of Canada. Connections to the city of Los Angeles within the band Seventh Heaven allowed Brent to have the opportunity to seek work in that market as a performer and session player.
Working with previous Shake Naked vocalist Lenita Erickson later proved fruitful as Lenita's friend Bruce Kulick of Kiss fame invited Brent to join him in a recording effort after hearing him play. That band would become known as Union and would also include John Corabi on vocals formerly of The Scream and Mötley Crüe, Jamie Hunting of David Lee Roth on bass, as well as Bruce on guitar. Brent briefly played in Bulletboys in 2000 , as well as recorded and toured with Gilby Clarke of Guns 'N Roses fame.
Brent would later receive an invitation to tour with Vince Neil's solo act as drummer and keyboardist.[ Performing on several international tours, Brent appeared in a live performance with Vince on VH1's TV show "Remaking: Vince Neil" in 2004.
After leaving the Vince Neil team Brent hooked up with Theory of a Deadman as their touring drummer. Brent appeared in four music videos with the band, as well as made several TV appearances including The Tonight Show With Jay Leno.. Brent played piano and sang with the band for several acoustic performances as well.
Brent has since been performing with Alice Cooper while drummer Eric Singer does some dates with Kiss, as well performing with Harlequin, and Indigenous . As of August 2007, Brent has announced his joining of Canadian rock act Econoline Crush. Although Brent is officially in Econoline Crush, he remains a backup drummer with Alice Cooper and infrequently tours with him.
2009年1月20日星期二
Center tap
In electronics, a center tap is a connection made to a point half way along a winding of a transformer or inductor, or along the element of a resistor or a potentiometer. Taps are sometimes used on inductors for the coupling of signals, and may not necessarily be at the half-way point, but rather, closer to one end. A common application of this is in the Colpitts oscillator. Inductors with taps also permit the transformation of the amplitude of alternating current (AC) voltages for the purpose of power conversion, in which case, they are referred to as autotransformers, since there is only one winding. An example of an autotransformer is an automobile ignition coil. Potentiometer tapping provides one or more connections along the device's element, along with the usual connections at each of the two ends of the element, and the slider connection. Potentiometer taps allow for circuit functions that would otherwise not be available with the usual construction of just the two end connections and one slider connection.
Volts center tapped (VCT) describes the voltage output of a center tapped transformer. For example: A 24VCT transformer will measure 24 VAC across the outer two taps (winding as a whole), and 12VAC from each outer tap to the center-tap (half winding). These two 12VAC supplies are 180 degrees out of phase with each other, thus making it easy to derive positive and negative 12 volt DC power supplies from them.
Common applications of center-tapped transformers
In a rectifier, a center-tapped transformer and two diodes can form a full-wave rectifier that allows both half-cycles of the AC waveform to contribute to the direct current, making it smoother than a half-wave rectifier. This form of circuit saves on rectifier diodes compared to a diode bridge, but has poorer utilization of the transformer windings. Center-tapped two-diode rectifiers were a common feature of power supplies in vacuum tube equipment. Modern semiconductor diodes are low-cost and compact so usually a 4-diode bridge is used (up to a few hundred watts total output) which produces the same quality of DC as the center-tapped configuration with a more compact and cheaper power transformer. Center-tapped configurations may still be used in high-current applications, such as large automotive battery chargers, where the extra transformer cost is offset by less costly rectifiers.
In an audio power amplifier center-tapped transformers are used to drive push-pull output stages. This allows two devices operating in Class B to combine their output to produce higher audio power with relatively low distortion. Design of such audio output transformers must tolerate a small amount of direct current that may pass through the winding.
Hundreds of millions of pocket-size transistor radios used this form of amplifier since the required transformers were very small and the design saved the extra cost and bulk of an output coupling capacitor that would be required for an output-transformerless design. However, since low-distortion high-power transformers are costly and heavy, most consumer audio products now use a transformerless output stage.
The technique is nearly as old as electronic amplification and is well-documented, for example, in "The Radiotron Designer's Handbook, Third Edition" of 1940.
In electronic amplifiers, a center-tapped transformer is used as a phase splitter in coupling different stages of an amplifier.
Power distribution, see 3 wire single phase.
A Centre tapped rectifier is preferred to the full bridge rectifier when the output dc current is high and the output voltage is low.
Volts center tapped (VCT) describes the voltage output of a center tapped transformer. For example: A 24VCT transformer will measure 24 VAC across the outer two taps (winding as a whole), and 12VAC from each outer tap to the center-tap (half winding). These two 12VAC supplies are 180 degrees out of phase with each other, thus making it easy to derive positive and negative 12 volt DC power supplies from them.
Common applications of center-tapped transformers
In a rectifier, a center-tapped transformer and two diodes can form a full-wave rectifier that allows both half-cycles of the AC waveform to contribute to the direct current, making it smoother than a half-wave rectifier. This form of circuit saves on rectifier diodes compared to a diode bridge, but has poorer utilization of the transformer windings. Center-tapped two-diode rectifiers were a common feature of power supplies in vacuum tube equipment. Modern semiconductor diodes are low-cost and compact so usually a 4-diode bridge is used (up to a few hundred watts total output) which produces the same quality of DC as the center-tapped configuration with a more compact and cheaper power transformer. Center-tapped configurations may still be used in high-current applications, such as large automotive battery chargers, where the extra transformer cost is offset by less costly rectifiers.
In an audio power amplifier center-tapped transformers are used to drive push-pull output stages. This allows two devices operating in Class B to combine their output to produce higher audio power with relatively low distortion. Design of such audio output transformers must tolerate a small amount of direct current that may pass through the winding.
Hundreds of millions of pocket-size transistor radios used this form of amplifier since the required transformers were very small and the design saved the extra cost and bulk of an output coupling capacitor that would be required for an output-transformerless design. However, since low-distortion high-power transformers are costly and heavy, most consumer audio products now use a transformerless output stage.
The technique is nearly as old as electronic amplification and is well-documented, for example, in "The Radiotron Designer's Handbook, Third Edition" of 1940.
In electronic amplifiers, a center-tapped transformer is used as a phase splitter in coupling different stages of an amplifier.
Power distribution, see 3 wire single phase.
A Centre tapped rectifier is preferred to the full bridge rectifier when the output dc current is high and the output voltage is low.
Madrid-Sevilla high-speed rail line
The Madrid-Sevilla high speed line is a 472 kilometers (293 mi) Spanish railway line for high speed traffic between Madrid and Seville. The first Spanish high-speed rail connection has been in use since 21 April 1992 at speeds up to 300 km/h (186 mph). Travel time between the two end points was reduced by over half.
At Córdoba the Madrid-Málaga high-speed rail line leaves the line from Madrid.
Routing
The line starts at Madrid-Atocha and runs over 31 bridges (total length 9,845 meters (32,300 ft)) and through 17 tunnels (total length 16.03 kilometers (10 mi), crossing the plains of Castile. It climbs south of Toledo as well as when crossing the Sierra Morena to an altitude of 800 meters, and then descends to around sea level as it approaches Seville. End point of the line is the new railway station Santa Justa in Seville.
Technical details
The high speed line was constructed at standard gauge, in contrast with the rest of the Spanish railway network. Voltage is 25 kV AC instead of 3000 V DC. Twelve transformers feed the overhead wires. Some 8 kilometers (5 mi) before the start and end points of the line, the line merges with local DC tracks.
The line was equipped with signalling standards that had been developed in the 80s for the German Hanover-Würzburg high-speed rail line and the Mannheim-Stuttgart high-speed rail line.
At the end of 2006, Spanish governmental agency ADIF ordered technical changes to the safety systems along the line for an amount of 12.6 million Euros, so that in the future, trains of the RENFE-type 104 will be able to run at 200 instead of 180 km/h. A further amount of 4.1 million Euros has been spent on changes to the ASFA train safety system.
Between the railway stations along the line, passing stations and emergency stations are located (in Spanish: Puesto de adelantamiento y estacionamiento de trenes, abbr. PEAT). These allow faster trains to overtake slower trains, and the parking of rescue trains. In addition, most of these stations have basic platforms that can be used to let passengers descend and change to buses in case of emergency.
Welding power supply
A welding power supply is a device that provides an electric current to perform welding. Welding usually requires high current (over 80 amperes) and it can need above 12,000 amps in spot welding. Low current can also be used; welding two razor blades together at 5 amps with gas tungsten arc welding is a good example. A welding power supply can be as simple as a car battery and as sophisticated as a modern machine based on silicon controlled rectifier technology with additional logic to assist in the welding process.
Classification
Welding machines are usually classified as constant current (CC) or constant voltage (CV); a constant current machine varies its output voltage to maintain a steady current while a constant voltage machine will fluctuate its output current to maintain a set voltage. Shielded metal arc welding will use a constant current source and gas metal arc welding and flux-cored arc welding typically use constant voltage sources but constant current is also possible with a voltage sensing wire feeder.
The nature of the CV machine is required by gas metal arc welding and flux-cored arc welding because the welder is not able to control the arc length manually. If a welder attempted to use a CV machine to weld with shielded metal arc welding the small fluctuations in the arc distance would cause wide fluctuations in the machine's output. With a CC machine the welder can count on a fixed number of amps reaching the material to be welded regardless of the arc distance but too much distance will cause poor welding.
Machine construction
Most welding machines are of the following designs:
Transformer
A transformer style welding machine converts the high voltage and low current electricity from the utility into a high current and low voltage, typically between 17 to 45 volts and 190 to 590 amps. This type of machine typically allows the welder to select the output current by either moving the core of the transformer in and out of the magnetic field or by allowing the welder to select from a set of taps on the transformer. These machines are typically the least expensive to purchase for hobbyist use.
Generator and alternator
Welding machines may also use generators or alternators to convert mechanical energy into electrical energy. Modern machines of this type are usually driven by an internal combustion engine but some older machines may also use an electric motor to drive the alternator or generator. In this configuration the utility power is converted first into mechanical energy then back into electrical energy to achieve the step-down effect similar to a transformer. Because the output of the generator can be direct current, these older machines can produce DC from AC without any need for rectifiers of any type.
Inverter
Since the advent of high-power semiconductors such as the IGBT, it is now possible to build a switching power supply capable of coping with the high loads of arc welding. These are known as inverter welding units. These supplies generally convert utility power to high voltage and store this energy in a capacitor bank; a microprocessor controller then switches this energy into a second transformer as needed to produce the desired welding current. The switching frequency is very high - typically 10,000 Hz or higher. The high frequency inverter-based welding machines can be more efficient and have better control than non-inverter welding machines.
The IGBTs in an inverter based machine are controlled by a microcontroller, so the electrical characteristics of the welding power can be changed by software in real time updates. Typically the controller software will implement features such as pulsing the welding current, variable ratios and current densities through a welding cycle, variable frequencies, and automatic spot-welding; all of which would be prohibitively expensive in a transformer-based machine but require only program space in software-controlled inverter machine.
Classification
Welding machines are usually classified as constant current (CC) or constant voltage (CV); a constant current machine varies its output voltage to maintain a steady current while a constant voltage machine will fluctuate its output current to maintain a set voltage. Shielded metal arc welding will use a constant current source and gas metal arc welding and flux-cored arc welding typically use constant voltage sources but constant current is also possible with a voltage sensing wire feeder.
The nature of the CV machine is required by gas metal arc welding and flux-cored arc welding because the welder is not able to control the arc length manually. If a welder attempted to use a CV machine to weld with shielded metal arc welding the small fluctuations in the arc distance would cause wide fluctuations in the machine's output. With a CC machine the welder can count on a fixed number of amps reaching the material to be welded regardless of the arc distance but too much distance will cause poor welding.
Machine construction
Most welding machines are of the following designs:
Transformer
A transformer style welding machine converts the high voltage and low current electricity from the utility into a high current and low voltage, typically between 17 to 45 volts and 190 to 590 amps. This type of machine typically allows the welder to select the output current by either moving the core of the transformer in and out of the magnetic field or by allowing the welder to select from a set of taps on the transformer. These machines are typically the least expensive to purchase for hobbyist use.
Generator and alternator
Welding machines may also use generators or alternators to convert mechanical energy into electrical energy. Modern machines of this type are usually driven by an internal combustion engine but some older machines may also use an electric motor to drive the alternator or generator. In this configuration the utility power is converted first into mechanical energy then back into electrical energy to achieve the step-down effect similar to a transformer. Because the output of the generator can be direct current, these older machines can produce DC from AC without any need for rectifiers of any type.
Inverter
Since the advent of high-power semiconductors such as the IGBT, it is now possible to build a switching power supply capable of coping with the high loads of arc welding. These are known as inverter welding units. These supplies generally convert utility power to high voltage and store this energy in a capacitor bank; a microprocessor controller then switches this energy into a second transformer as needed to produce the desired welding current. The switching frequency is very high - typically 10,000 Hz or higher. The high frequency inverter-based welding machines can be more efficient and have better control than non-inverter welding machines.
The IGBTs in an inverter based machine are controlled by a microcontroller, so the electrical characteristics of the welding power can be changed by software in real time updates. Typically the controller software will implement features such as pulsing the welding current, variable ratios and current densities through a welding cycle, variable frequencies, and automatic spot-welding; all of which would be prohibitively expensive in a transformer-based machine but require only program space in software-controlled inverter machine.
Ammeter
An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A), hence the name.
The earliest design is the D'Arsonval galvanometer or moving coil ammeter. It uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The voltage drop across the coil is kept to a minimum to minimize resistance across the ammeter in any circuit into which it is inserted.
Moving iron ammeters use a piece of iron which move when acted upon by the electromagnetic force of a fixed coil of wire. This type of meter responds to both direct and alternating currents (as opposed to the moving coil ammeter, which works on direct current only).
To measure larger currents, a resistor called a shunt is placed in parallel with the meter. Most of the current flows through the shunt, and only a small fraction flows through the meter. This allows the meter to measure large currents. Traditionally, the meter used with a shunt has a full-scale deflection (FSD) of 50 mV, so shunts are typically designed to produce a voltage drop of 50 mV when carrying their full rated current.
Zero-center ammeters are used for applications requiring current to be measured with both polarities, common in scientific and industrial equipment. Zero-center ammeters are also commonly placed in series with a battery. In this application, the charging of the battery deflects the needle to one side of the scale (commonly, the right side) and the discharging of the battery deflects the needle to the other side.
Digital ammeter designs use an analog to digital converter (ADC) to measure the voltage across the shunt resistor; the digital display is calibrated to read the current through the shunt.
Since the ammeter shunt has a very low resistance, mistakenly wiring the ammeter in parallel with a voltage source will cause a short circuit, at best blowing a fuse, possibly damaging the instrument and wiring, and exposing an observer to injury. In AC circuits, a current transformer converts the magnetic field around a conductor into a small AC current, typically either 1 or 5 Amps at full rated current, that can be easily read by a meter. In a similar way, accurate AC/DC non-contact ammeters have been constructed using Hall effect magnetic field sensors. A portable hand-held clamp-on ammeter is a common tool for maintenance of industrial and commercial electrical equipment, which is temporarily clipped over a wire to measure current.
Magnetic amplifier
The magnetic amplifier (colloquially known as the "mag amp") is an electromagnetic device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to vacuum tube amplifiers where robustness and high current capacity were required. World War II Germany perfected this type of amplifier, and it was used for instance in the V-2 rocket. The magnetic amplifier has now been largely superseded by the transistor-based amplifier, except in a few safety critical, high reliability or extremely demanding applications.
Principle of operation
The mag amp is a "magnetic field" kind of amplifier and is of Class H type.
Visually a mag amp device may resemble a transformer but the operating principle is quite different from a transformer - essentially the mag amp is a saturable reactor. It makes use of magnetic saturation of the core, a non-linear property of a certain class of transformer cores. For controlled saturation characteristics the magnetic amplifier employs core materials that have been designed to have a specific B-H curve shape that is highly rectangular, in contrast to the slowly tapering B-H curve of softly saturating core materials that are often used in normal transformers.
The typical magnetic amplifier consists of two physically separate but similar transformer magnetic cores, each of which has two windings - a control winding and an AC winding. A small DC current from a low impedance source is fed into the series-connected control windings. An AC voltage is fed into one AC winding, with the other AC winding connected to the load. The AC windings may be connected either in series or in parallel, the configurations resulting in different types of mag amps. The amount of control current fed into the control winding sets the point in the AC winding waveform at which either core will saturate. In saturation, the AC winding on the saturated core will go from a high impedance state ("off") into a very low impedance state ("on") - that is, the control current controls at which voltage the mag amp switches "on".
A relatively small DC current on the control winding is able to control or switch large AC currents on the AC windings. This results in current amplification.
Applications
Magnetic amplifiers were used extensively as the switching element in early switched-mode (SMPS) power supplies, as well as in lighting control. They have been largely superseded by semiconductor based solid-state switches, though recently there has been some regained interest in using mag amps in compact and reliable switching power supplies. PC ATX power supplies often use mag amps for secondary side voltage regulation.
Magnetic amplifiers are still used in some arc welders.
Magnetic amplifier transformer cores designed specifically for switch mode power supplies are currently manufactured by several large electromagnetics companies, including Metglas and Mag-Inc.
Magnetic amplifiers can be used for measuring high DC-voltages without direct connection to the high voltage and are therefore still used in the HVDC-technique.
Another small book on the subject of Magnetic amplifiers by the US Navy (1951)
Misnomer uses
Late in the 20th century, Robert Carver designed and produced several high quality high powered audio amplifiers, calling them magnetic amplifiers. In fact, they were in most respects conventional audio amplifier designs with an unusual power supply circuit. They were not magnetic amplfiers in the sense of this article.
References
^ Abraham I. Pressman (1997). Switching Power Supply Design. McGraw-Hill. ISBN 0-07-052236-7.
^ George B. Trinkaus (2000). Magnetic Amplifiers. High Voltage Press. ISBN 0-9709618-5-5.
Principle of operation
The mag amp is a "magnetic field" kind of amplifier and is of Class H type.
Visually a mag amp device may resemble a transformer but the operating principle is quite different from a transformer - essentially the mag amp is a saturable reactor. It makes use of magnetic saturation of the core, a non-linear property of a certain class of transformer cores. For controlled saturation characteristics the magnetic amplifier employs core materials that have been designed to have a specific B-H curve shape that is highly rectangular, in contrast to the slowly tapering B-H curve of softly saturating core materials that are often used in normal transformers.
The typical magnetic amplifier consists of two physically separate but similar transformer magnetic cores, each of which has two windings - a control winding and an AC winding. A small DC current from a low impedance source is fed into the series-connected control windings. An AC voltage is fed into one AC winding, with the other AC winding connected to the load. The AC windings may be connected either in series or in parallel, the configurations resulting in different types of mag amps. The amount of control current fed into the control winding sets the point in the AC winding waveform at which either core will saturate. In saturation, the AC winding on the saturated core will go from a high impedance state ("off") into a very low impedance state ("on") - that is, the control current controls at which voltage the mag amp switches "on".
A relatively small DC current on the control winding is able to control or switch large AC currents on the AC windings. This results in current amplification.
Applications
Magnetic amplifiers were used extensively as the switching element in early switched-mode (SMPS) power supplies, as well as in lighting control. They have been largely superseded by semiconductor based solid-state switches, though recently there has been some regained interest in using mag amps in compact and reliable switching power supplies. PC ATX power supplies often use mag amps for secondary side voltage regulation.
Magnetic amplifiers are still used in some arc welders.
Magnetic amplifier transformer cores designed specifically for switch mode power supplies are currently manufactured by several large electromagnetics companies, including Metglas and Mag-Inc.
Magnetic amplifiers can be used for measuring high DC-voltages without direct connection to the high voltage and are therefore still used in the HVDC-technique.
Another small book on the subject of Magnetic amplifiers by the US Navy (1951)
Misnomer uses
Late in the 20th century, Robert Carver designed and produced several high quality high powered audio amplifiers, calling them magnetic amplifiers. In fact, they were in most respects conventional audio amplifier designs with an unusual power supply circuit. They were not magnetic amplfiers in the sense of this article.
References
^ Abraham I. Pressman (1997). Switching Power Supply Design. McGraw-Hill. ISBN 0-07-052236-7.
^ George B. Trinkaus (2000). Magnetic Amplifiers. High Voltage Press. ISBN 0-9709618-5-5.
Head end power
Head end power (HEP) or electric train supply (ETS) is a rail transport term for the electrical power distribution system on a passenger train. The power source, usually a locomotive at the front or “head” of a train or a generator car, generates all the electricity used for lightening, electrical and other "hotel" needs. The maritime equivalent is Hotel Electric Power (HEP).
UK
Originally, trains hauled by a steam locomotive would be provided with a supply of steam from the locomotive's boiler for heating the carriages. When diesel locomotives and electric locomotives replaced steam, the steam heating was then supplied by a steam-heat boiler. This was oil-fired (in diesel locomotives) or heated by an electric element (in electric locomotives). Oil-fired steam-heat boilers were appallingly unreliable. They caused more locomotive failures on any class to which they were fitted than any other system or component of the locomotive, and this was a major incentive to adopt a more reliable method of carriage heating.
At this time, lighting was powered by batteries which were charged by a dynamo underneath each carriage when the train was in motion, and buffet cars would use bottled gas for cooking and water heating.
On modern Diesel multiple unit trains, such as the Virgin Trains Voyager, the engine mounted below each vehicle provides power for that vehicle.
Electric Train Heat (ETH) and Electric Train Supply (ETS)
Later diesels and electric locomotives were equipped with Electric Train Heating (ETH) apparatus, which supplied electrical power to the carriages to run electric heating elements installed alongside the steam-heat apparatus, which was retained for use with older locomotives. Later carriage designs abolished the steam-heat apparatus, and made use of the ETH supply not only for heating, but also to power lighting, ventilation, air conditioning, fans, sockets and kitchen equipment in the train. In recognition of this ETH was eventually renamed Electric Train Supply (ETS).
Each coach has an index relating to the maximum consumption of electricity that that coach could use. The sum of all the indices must not exceed the index of the locomotive. One "ETH index unit" equals 5kW; a locomotive with an ETH index of 95 can supply 475kW of electrical power to the train.
USA
During the age of steam, cars were heated by low pressure saturated steam supplied by the locomotive. Electricity for car lighting and ventilation was derived from batteries charged by axle-driven generators on each car or from engine-generator sets mounted under the carbody.
The first advance over this system was developed on the Boston and Maine Railroad, which had placed a number of steam locomotives and passenger cars into dedicated commuter service in Boston. It was discovered that due to the low average speeds and frequent stops characteristic of commuter operation, axle generators did not produce enough output to keep the batteries adequately charged, resulting frequent passenger complaints about lighting and ventilation failures. In response, the railroad fitted higher capacity generators to the locomotives assigned to pull these trains and arranged electrical connections to transmit the generators' output back to the cars. The cars still depended on steam from the locomotive for heating.
When Diesel locomotives were introduced to passenger service, they were equipped with steam generators to provide steam for car heating. However, the use of axle generators and batteries persisted for many years. This started to change in the late 1950s, during which time the Chicago and North Western Railway removed the steam generators from their EMD F7 and E8 locomotives in commuter service and installed Diesel generator sets. This was a natural evolution, as their commuter trains were already receiving low voltage, low amperage power from the locomotives to assist axle generators in maintaining battery charge. In some cases, commuter cars were equipped with propane engine-powered air conditioning. The resulting separate systems of lighting power, steam heat, and engine-driven air conditioning increased the maintenance workload, as well as parts proliferation, thus leading to the full-scale adoption of HEP, where a single power source would handle all these functions.
While commuter fleets were quickly converted to HEP, long distance trains continued to operate with steam heat and battery-powered electrical systems. This gradually changed following the transfer of intercity passenger rail service to Amtrak, ultimately resulting in full adoption of HEP in the USA and the discontinuation of the old systems.
Following its formation in 1971, Amtrak's initial locomotive purchase was the Electro-Motive (EMD) SDP40F, an adaptation of the widely-used SD40-2 3000 horsepower freight locomotive, fitted with a passenger style carbody and steam generating capability. The SDP40F permitted the use of modern motive power in conjunction with the old steam heated passenger rolling stock acquired from private railroads, giving Amtrak time to procure purpose-built cars and locomotives.
In 1975, Amtrak started to take delivery of the all-electric Amfleet car, hauled by General Electric (GE) P30CH and, later, EMD F40PH locomotives, both unit types being equipped to furnish HEP. Following the introduction of the Amfleet fleet, the (also all-electric) Superliner was placed into operation for servicing long-distance western routes. Amtrak subsequently converted a portion of the steam heated fleet to all-electric operation using HEP and retired the remaining unconverted cars.
Engine
The HEP generator can be driven by either a separate engine mounted in the locomotive or generator car, or by the locomotive's prime mover.
Separate engines
Engine types vary, but in the US, they are mainly Caterpillar 3412 V12 and Cummins K-Series Inline 6 models. In the past, Detroit Diesel 8V-71 and 12V-71 engines were also used. Such engine/generator sets are generally installed in a compartment in the rear of the locomotive that is isolated from the main engine room, drawing fuel from the locomotive's fuel tanks.
Smaller under-car engine/generator sets for providing electricity on short trains are also manufactured, Stadco being one popular brand.
Locomotive prime mover
In many applications, the locomotive's prime mover provides both propulsion and head end power. In most cases, the prime mover must run at a constant speed (RPM) to maintain the required 50 Hz or 60 Hz AC line frequency. For example, an EMD locomotive operating in HEP mode will run the prime mover at a constant 900 RPM (which is full RPM), driving the generator at 1500 RPM (50 Hz) or 1800 RPM (60 Hz) through a gearbox. For noise reduction purposes, the locomotive's main (traction) generator can also be configured to supply HEP, usually at 600 or 720 RPM. However, this mode is only available when the locomotive is stationary.
The advent of power electronics has allowed the prime mover to operate over a larger speed range and still supply a constant HEP voltage and frequency by means of inverters.
When derived from the prime mover, HEP is generated at the expense of traction power. For example, the General Electric 3200 horsepower (2.4 MW) P32 and 4000 horsepower (3.0 MW) Genesis-Series P40 locomotives are derated to 2900 (2.2 MW) and 3650 horsepower (2.72 MW), respectively, when supplying HEP.
Electrical loading
HEP power supplies the lighting, HVAC, dining car kitchen and battery charging loads. Individual car electrical loading ranges from 20 kW for a typical car to more than 150 kW for a Dome car with kitchen and dining area, such as Princess Tours Ultra-Dome cars operating in Alaska.
Because of the lengths of trains and the high power requirements, HEP is supplied, in North America, as three-phase AC at 480-V (standard in the US and for Canada's VIA), 575-V (GO Transit, Toronto), or rarely 600-V. Transformers are fitted in each car for reduction to lower voltages.
In the UK, ETS is supplied at 800-V to 1000-V AC/DC two pole (400 or 600-A), 1500-V AC two pole (800-A) or at 415-V 3 phase on the HST
Alternatives
Although most locomotive-hauled trains take power directly from the locomotive, there have been examples (mainly in continental Europe) where restaurant cars would take power directly from the overhead wires.
UK
Originally, trains hauled by a steam locomotive would be provided with a supply of steam from the locomotive's boiler for heating the carriages. When diesel locomotives and electric locomotives replaced steam, the steam heating was then supplied by a steam-heat boiler. This was oil-fired (in diesel locomotives) or heated by an electric element (in electric locomotives). Oil-fired steam-heat boilers were appallingly unreliable. They caused more locomotive failures on any class to which they were fitted than any other system or component of the locomotive, and this was a major incentive to adopt a more reliable method of carriage heating.
At this time, lighting was powered by batteries which were charged by a dynamo underneath each carriage when the train was in motion, and buffet cars would use bottled gas for cooking and water heating.
On modern Diesel multiple unit trains, such as the Virgin Trains Voyager, the engine mounted below each vehicle provides power for that vehicle.
Electric Train Heat (ETH) and Electric Train Supply (ETS)
Later diesels and electric locomotives were equipped with Electric Train Heating (ETH) apparatus, which supplied electrical power to the carriages to run electric heating elements installed alongside the steam-heat apparatus, which was retained for use with older locomotives. Later carriage designs abolished the steam-heat apparatus, and made use of the ETH supply not only for heating, but also to power lighting, ventilation, air conditioning, fans, sockets and kitchen equipment in the train. In recognition of this ETH was eventually renamed Electric Train Supply (ETS).
Each coach has an index relating to the maximum consumption of electricity that that coach could use. The sum of all the indices must not exceed the index of the locomotive. One "ETH index unit" equals 5kW; a locomotive with an ETH index of 95 can supply 475kW of electrical power to the train.
USA
During the age of steam, cars were heated by low pressure saturated steam supplied by the locomotive. Electricity for car lighting and ventilation was derived from batteries charged by axle-driven generators on each car or from engine-generator sets mounted under the carbody.
The first advance over this system was developed on the Boston and Maine Railroad, which had placed a number of steam locomotives and passenger cars into dedicated commuter service in Boston. It was discovered that due to the low average speeds and frequent stops characteristic of commuter operation, axle generators did not produce enough output to keep the batteries adequately charged, resulting frequent passenger complaints about lighting and ventilation failures. In response, the railroad fitted higher capacity generators to the locomotives assigned to pull these trains and arranged electrical connections to transmit the generators' output back to the cars. The cars still depended on steam from the locomotive for heating.
When Diesel locomotives were introduced to passenger service, they were equipped with steam generators to provide steam for car heating. However, the use of axle generators and batteries persisted for many years. This started to change in the late 1950s, during which time the Chicago and North Western Railway removed the steam generators from their EMD F7 and E8 locomotives in commuter service and installed Diesel generator sets. This was a natural evolution, as their commuter trains were already receiving low voltage, low amperage power from the locomotives to assist axle generators in maintaining battery charge. In some cases, commuter cars were equipped with propane engine-powered air conditioning. The resulting separate systems of lighting power, steam heat, and engine-driven air conditioning increased the maintenance workload, as well as parts proliferation, thus leading to the full-scale adoption of HEP, where a single power source would handle all these functions.
While commuter fleets were quickly converted to HEP, long distance trains continued to operate with steam heat and battery-powered electrical systems. This gradually changed following the transfer of intercity passenger rail service to Amtrak, ultimately resulting in full adoption of HEP in the USA and the discontinuation of the old systems.
Following its formation in 1971, Amtrak's initial locomotive purchase was the Electro-Motive (EMD) SDP40F, an adaptation of the widely-used SD40-2 3000 horsepower freight locomotive, fitted with a passenger style carbody and steam generating capability. The SDP40F permitted the use of modern motive power in conjunction with the old steam heated passenger rolling stock acquired from private railroads, giving Amtrak time to procure purpose-built cars and locomotives.
In 1975, Amtrak started to take delivery of the all-electric Amfleet car, hauled by General Electric (GE) P30CH and, later, EMD F40PH locomotives, both unit types being equipped to furnish HEP. Following the introduction of the Amfleet fleet, the (also all-electric) Superliner was placed into operation for servicing long-distance western routes. Amtrak subsequently converted a portion of the steam heated fleet to all-electric operation using HEP and retired the remaining unconverted cars.
Engine
The HEP generator can be driven by either a separate engine mounted in the locomotive or generator car, or by the locomotive's prime mover.
Separate engines
Engine types vary, but in the US, they are mainly Caterpillar 3412 V12 and Cummins K-Series Inline 6 models. In the past, Detroit Diesel 8V-71 and 12V-71 engines were also used. Such engine/generator sets are generally installed in a compartment in the rear of the locomotive that is isolated from the main engine room, drawing fuel from the locomotive's fuel tanks.
Smaller under-car engine/generator sets for providing electricity on short trains are also manufactured, Stadco being one popular brand.
Locomotive prime mover
In many applications, the locomotive's prime mover provides both propulsion and head end power. In most cases, the prime mover must run at a constant speed (RPM) to maintain the required 50 Hz or 60 Hz AC line frequency. For example, an EMD locomotive operating in HEP mode will run the prime mover at a constant 900 RPM (which is full RPM), driving the generator at 1500 RPM (50 Hz) or 1800 RPM (60 Hz) through a gearbox. For noise reduction purposes, the locomotive's main (traction) generator can also be configured to supply HEP, usually at 600 or 720 RPM. However, this mode is only available when the locomotive is stationary.
The advent of power electronics has allowed the prime mover to operate over a larger speed range and still supply a constant HEP voltage and frequency by means of inverters.
When derived from the prime mover, HEP is generated at the expense of traction power. For example, the General Electric 3200 horsepower (2.4 MW) P32 and 4000 horsepower (3.0 MW) Genesis-Series P40 locomotives are derated to 2900 (2.2 MW) and 3650 horsepower (2.72 MW), respectively, when supplying HEP.
Electrical loading
HEP power supplies the lighting, HVAC, dining car kitchen and battery charging loads. Individual car electrical loading ranges from 20 kW for a typical car to more than 150 kW for a Dome car with kitchen and dining area, such as Princess Tours Ultra-Dome cars operating in Alaska.
Because of the lengths of trains and the high power requirements, HEP is supplied, in North America, as three-phase AC at 480-V (standard in the US and for Canada's VIA), 575-V (GO Transit, Toronto), or rarely 600-V. Transformers are fitted in each car for reduction to lower voltages.
In the UK, ETS is supplied at 800-V to 1000-V AC/DC two pole (400 or 600-A), 1500-V AC two pole (800-A) or at 415-V 3 phase on the HST
Alternatives
Although most locomotive-hauled trains take power directly from the locomotive, there have been examples (mainly in continental Europe) where restaurant cars would take power directly from the overhead wires.
Bleeder resistor
A bleeder resistor is a resistor placed in parallel with a high-voltage supply for the purposes of discharging the energy stored in the power source's filter capacitors or other components that store electrical energy when the equipment is turned off.
It is a use for a standard resistor rather than a separate type of component.
Usage
DC power supplies
Power supplies, especially switchmode power supplies, use a bridge rectifier and a large filter capacitor to convert mains AC power into DC for the chopper. When power is removed, any residual charge in the filter capacitor is dissipated through the bleeder resistor.
High voltage supply in television sets
The bleeder resistor commonly found inside a flyback transformer that supplies high voltage for a CRT is valued in the hundreds of megohms range, and can therefore not be measured with the common technician's multimeter.
Instead of a resistor inside the transformer, the focus and screen control array may be used for the same purpose, depending on the application and tolerances of the type of tube it is producing output for.
These bleeders discharge the focus supply, but not the high voltage final anode feed.
Failure
The failure of a bleeder resistor prevents the discharge of the capacitors, resulting in dangerous voltages being retained for many days. This is one of several reasons for the typical warning on most equipment: "Warning - No user-serviceable parts inside". An un-suspecting user may get an electrical shock from opened equipment due to failure of a bleeder resistor, or the common practice of not fitting them.
Technical considerations
There is always a trade-off between the speed with which the bleeder operates and the amount of power wasted in the bleeder; a faster bleed-down rate wastes more power during normal, power-on operation.
Dual bleeder
Because of the speed/power tradeoff, high-powered circuits may use two separate bleeder circuits. A fast bleed circuit is switched out during normal operation so that no power is wasted; when power is switched off, the fast bleeder is connected, rapidly bleeding down the voltage. The switch controlling the fast bleeder can fail, either by connecting when it shouldn't (and overheating) or by not connecting when it should (and thereby failing to bleed off the voltage quickly). To avoid the risk of not having an operational bleeder, a secondary, slower (and less lossy) bleeder is usually permanently connected so that there is always some bleed-down capability.
It is a use for a standard resistor rather than a separate type of component.
Usage
DC power supplies
Power supplies, especially switchmode power supplies, use a bridge rectifier and a large filter capacitor to convert mains AC power into DC for the chopper. When power is removed, any residual charge in the filter capacitor is dissipated through the bleeder resistor.
High voltage supply in television sets
The bleeder resistor commonly found inside a flyback transformer that supplies high voltage for a CRT is valued in the hundreds of megohms range, and can therefore not be measured with the common technician's multimeter.
Instead of a resistor inside the transformer, the focus and screen control array may be used for the same purpose, depending on the application and tolerances of the type of tube it is producing output for.
These bleeders discharge the focus supply, but not the high voltage final anode feed.
Failure
The failure of a bleeder resistor prevents the discharge of the capacitors, resulting in dangerous voltages being retained for many days. This is one of several reasons for the typical warning on most equipment: "Warning - No user-serviceable parts inside". An un-suspecting user may get an electrical shock from opened equipment due to failure of a bleeder resistor, or the common practice of not fitting them.
Technical considerations
There is always a trade-off between the speed with which the bleeder operates and the amount of power wasted in the bleeder; a faster bleed-down rate wastes more power during normal, power-on operation.
Dual bleeder
Because of the speed/power tradeoff, high-powered circuits may use two separate bleeder circuits. A fast bleed circuit is switched out during normal operation so that no power is wasted; when power is switched off, the fast bleeder is connected, rapidly bleeding down the voltage. The switch controlling the fast bleeder can fail, either by connecting when it shouldn't (and overheating) or by not connecting when it should (and thereby failing to bleed off the voltage quickly). To avoid the risk of not having an operational bleeder, a secondary, slower (and less lossy) bleeder is usually permanently connected so that there is always some bleed-down capability.
WEG Industries
WEG is a multinational corporation headquartered in Jaraguá do Sul, Brazil, operating mainly in the electric engineering, power and automation technology areas.
WEG is the largest industrial electric motor manufacturer in the Americas and one of the largest manufacturers of electric motors in the world producing over ten million units annually. . WEG has operations in around 100 countries, with approximately 20,000 employees (2008).
WEG is traded on the Stock Exchange of São Paulo (Bovespa) in Brazil.
History
The german word weg means "way".
The state of Santa Catarina in Brazil was subjected to German colonization (besides Italian and - much earlier - Portuguese), which must have influenced the founders (Werner Ricardo Voigt, Eggon João da Silva and Geraldo Werninghaus) in their decision to use the acronym WEG, joining the three first letters of their names.
The company started on the 16th of September 1961, when the three founded "Eletromotores Jaraguá". Years later, the company created by an electrician, an administrator and a mechanic would change its name to "Eletromotores WEG SA".
Initially producing electric motors, WEG started incrementing its activities during the eighties, with the production of electric components, products for industrial automation, power and distribution transformers, liquid and powder paints and electrical insulatins varnishes. More and more the company is consolidating itself not only as a motor manufacturer, but also as a complete, industrial, electrical systems supplier.
In 1989 the three founders created the company's Board of Directors and Décio da Silva was chosen as WEG's CEO. Two years later WEG's Quality and Productivity Program was implemented, consolidating the process of participative administration.
Products
WEG products are present at almost every electric engineering interest area: - Generation (Generators, transformers and switchgear) - Transmission (EPC, switchgears, transformers) - Distribution (EPC, transformers) - Electric products (motors, switchgears, frequency inverters, AC/DC converters, contactors, fuses, circuit breakers and servomotors, among others) - Automation (Hardware and Software) - Integration Engineering with products of different manufacturers
Figures
Counting on more than 19 thousand employees all over the world, WEG reached an annual turnover of R$ 4,552 billion in 2007, a growth of 29% in relation to 2006, R$ 3,527 billion. Exports were responsible for 30% of the company's turnover.
Production is distributed in manufacturing plants in Brazil (in the cities of São Paulo, São Bernardo do Campo, Hortolândia, Guarulhos, Manaus, Guaramirim, Itajaí, Blumenau and two plants in Jaraguá do Sul, two in Argentina, one in Mexico , one in Portugal and one in China. WEG also exports to over 100 countries and counts on branches and technical assistance in all five continents.
On May, 2008, WEG has announced a new factory in India.
A good part of these great results influence life in the city of Jaraguá do Sul directly. One of the most visible forms of this is the distribution of profits to the employees. Besides the injection of capital that the profit distribution provokes in all the sectors of the economy, WEG also participates directly in the increase in quality of life of the city. A great part of this success is due to participative administration, a concept applied from the factory floor up. The Circles of Quality Control (CCQ), implemented in 1982, are already part of the company culture. Through these groups, each employee is able to present suggestions on job safety, health and quality of life. Many suggestions result in new production processes and even in new machines, generating more savings and productivity.
Centroweg
Another highlight is WEG's training department, which invests in courses, both internal and external, for the workers and new trainees from all branches over the world.
Created in 1968 to aid in the lack of qualified professionals in the area of mechanical engineers, "Centroweg" grew and diversified its activities along with WEG. Today, it gives technical courses in the areas of mechanical, electronics, electricity, robotics and chemistry (for high school students) and mechanical engineers for adults.
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