OPTICAL FIBER CABLE SPLICING

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HOW TO JOIN THE OFC 

1. Select the cable

2.Remove the outer insulation used proper tool

3.Skin the fiber 

4. clean the fiber use with spirit

5.Cut the fiber with cutter machine in proper length

6. Insert the cable in two sided with properly

7. Close the machine cover

8.start the splicing

9.After splicing the machine display indicates "remove Fiber"

10. Root the spliced fiber in Junction Box

FLEXIBLE PCB TECHNOLOGY

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Flexible-Circuit Technology

The advance of electronic systems into our everyday lives is evidence of a major digital technology revolution. The success stories of the personal computer and the mobile phone serve to demonstrate that consumer and business demand for innovative products are significant. Increasingly electrical and electronic systems are entering our lives in many unanticipated ways. They can be found in our homes in the form of cordless phones and digital TVs, in our cars in the form of hands-free communications and telematics, and in business in the form of notebook computers and mobile personal data assistants (PDAs).

Importantly, and also covertly, within the above applications flexible printed circuits have also been entering our lives. Traditionally employed in the role of wire replacement, removing the need for complex wire harnesses, and replacing costly and increasingly complicated wired assemblies, flexible circuits offer a much simpler and often significantly more cost-effective interconnection method.

 However, alongside increasingly innovative applications flexible-circuit technology is branching out significantly from this initial role and it is poised to be a technology that will provide enormous design freedoms for electronic engineers and product designers over the coming years. As the demands of modern electronic systems call for increasing functionality, greater circuit density, higher connectivity, better environmental performance, and all at lower cost, flexible circuitry is poised to deliver on the promise of twenty-first century electronics.

A Definition for Flexible Circuits

Confusion still exists regarding what constitutes a flexible circuit. When asked to envisage a flexible circuit, the image in most people’s mind will be of a bendy printed circuit, typically consisting of a flexible film with a pattern of copper conductors on it.

Whilst the image is not far from the truth, in order to better understand flexible circuits it is important at the outset to establish a working definition. The IPC (formerly the Institute for Interconnecting and Packaging Electronic Circuits), through its role of setting standards and guidelines for the electronics industry, has established such a definition:

Flexible Printed Circuit

A patterned arrangement of printed circuitry and components that utilizes flexible base material with or without flexible cover lay.

The above definition, although strictly accurate, does little justice to the complexity of the technology but does serve to convey some of the potential given the available variations in base materials, conductor materials, and protective finishes.

Flexible-Circuit Constituents

From the above definition, there are a number of basic material elements that constitute a flexible circuit: a dielectric substrate film (base material), electrical conductors (circuit traces), a protective finish (cover lay or cover coat), and, not least, adhesives to bond the various materials together. Together the above materials form a basic flexible-circuit laminate suitable for use as a simple wiring assembly, or capable after further processing of forming a compliant final circuit assembly.

Within a typical flexible-circuit construction the dielectric film forms the base layer, with adhesives used to bond the conductors to the dielectric and, in multilayer flexible circuits, to bond the individual layers together. Adhesives can also be used in a protective capacity to cover the final circuit to prevent the ingress of moisture and dirt, when they are termed ‘cover lays’ (also ‘cover layers’) or ‘cover coats’.

Materials Diversity Overview

Many individual materials exist that time and extensive prototyping have proven suitable for application in flexible circuits. There are numerous substrate materials(termed dielectrics) available as very thin films of 12–120 microns in thickness that have been prototyped as base materials upon which to build flexible circuits. However, the two most common dielectric substrate materials are polyester and polyimide. Both are widely available from a number of global sources and both have unique advantages that make them suitable as base materials.

At costs of pennies per square metre, polyester materials are used to provide millions of exceptionally low-cost flexible circuits that find their way into calculators, cameras, touch panels, keypads and automotive dashboards. Polyesters are also highly flexible and are the material of choice for dynamic flexing applications. One example is the connection between a notebook PC keyboard and its screen, an application where many thousands of flexing operations are required.

Single-Sided Flexible Circuits

Single-sided flexible circuits are the most common types of flexible circuit available. They consist of a single conductor layer on a flexible dielectric film with access to circuit-termination features accessible from one side only. They can be manufactured with or without cover lays and protective coatings, and their relatively simple design makes them highly cost effective. The conductors used can be conventional metal foil, or, for low-cost, polymer thick-film (PTF) ink can be used. This is simply printable conductive ink, loaded with carbon or silver particles, which is directly applied to the flexible substrate in the circuit pattern required by a v Single-sided circuits can offer the lowest cost and relative ease of production. Because of their thin and lightweight construction such circuits are best suited to dynamic- flexing or wiring-replacement applications such as computer printers and disk drives. Nearly all of the world’s calculators consist of PTF flexible circuits on polyester film, a combination that offers an exceptionally low circuit cost.ariety of printing and stencilling techniques.

OTDR - Optical Time Domain Reflectometer

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The architecture and the operation of the OTDR system

The OTDR is the most important investigation tool for optical fibres, which is applicable for the measurement of fibre loss, connector loss and for the determination of the exact place and the value of cabel discontinuities. By means of very short pulses it is also possible to measure the modal dispersion of multimodal fibres. The structure of a typical OTDR equipment is shown below:

The principal of the OTDR analyzer is the following: a short light pulse is transmitted into the fibre under test and the time of the incidence and the amplitude of the reflected pulses are measured. The commonly used pulse width ranges from nanosecs to microsecs, the power of the pulse can exceed 10 mW. The repetition frequency depends on the fibre length, typically is between 1 and 20 kHz, naturally it is smaller for longer fibres. The division by 2 at the inputs of oscilloscope is needed since both the vertical (loss) and the horizontal (length) scales correspond to the one-way length.

The components of the fibre loss and their importance in the OTDR measurements

There are three reasons for the fibre loss:

• absorption

• radiation loss

• Rayleigh scattering

The absorption creates 10-20% of the fibre loss. It mainly originates from the OH- ions inside the fibre material (impurities). With modern technologies the number of these contaminants, so the loss can be kept at relatively low level. The fibre loss increases dinamically for wavelengths above 1700 nm, thus this is the lowest frequency for optical telecommunications. In practice the 1300 and 1550 nm wavelengths are used as the insertion loss shows minimal values at these wavelengths. Naturally, absorption does not induce reflection, so if this would be the only physical phenomena, the fibre loss could be measured by the means of OTDR only with a well known, calibrated termination

In practice, the fibre continuously radiates backwards due to the Rayleigh scattering, which will be described later, so the absorption loss is measured together with the other losses.

Radiation loss occurs when the geometrical parameters of the fibre abruptly change, or a mechanical tension is present in the fibre material due to fabrication failure or mechanical impact. Considering appropriate fabrication technologies and fibre jacket, the radiation loss can be neglected and, like absorption, it does not create reflections, so from the OTDR measurements point of view it can handle as absorption losses. A high level discontinuity originated by e.g. strong folding, can be shown by OTDR as it produces high loss.

During OTDR measurements the most important loss is the one caused by Rayleigh scattering. It generates the 80-90% of the total loss. The scattering is induced by the microscopic inhomogenity of the refractive index of the fibre. These inhomogenities cause diffraction, so a certain part of the light energy is radiated isotropically. The level of the diffrection reaches its maximum when the wavelength is in the same range as the dimensions of the microscopic inhomogenities. Thus the level of the scattering decreases when the wavelength is increased. Among others this is the reason for using the 1300 and the 1550 nm ranges instead of the 850 nm. A certain part of the diffracted light propagates backwards in the fibre which is, when measured, carries important information. In the following, we calculate the ratio of the diffracted and the backward propagating light.

Electric panel

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HOW TO SELECT BUSBAR

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How to select busbar for electrical systems 

Busbar Voltage Drop

The Busbar voltage drop is the expected resistive voltage drop on a busbar circuit, based on the             length and cross sectional area of the bar. There may be an additional voltage drop due to the inductance of the bar. This can become particularly important at high frequencies and high currents. Where there are a number of bars in parallel, assume the bar width is the actual width multiplied by the number of bars in parallel. i.e. 5 bars of 50 x 6 mm in parallel would give the same resistive voltage drop as a single bar of 50 x 30mm.

To calculate the resistive voltage drop of a length of busbar, enter in the width, length and thickness of the bar. Select the units as either metric or imperial. and the current passing through the bar. The circuit configuration also needs to be specified. "Single bar" refers to the voltage drop along a single length of bar, while "Single Phase" refers to the voltage drop of two equal lengths of bar, one in the active circuit and one in the neutral circuit. "Three Phase" calculates the voltage drop between the supply and a three phase load where three equal bars are used for the three phase circuits. Enter the ambient temperature around the bar as Celsius or Fahrenheit and the program will check the suitability of the bar for that current. The program displays the resistive voltage drop for both an aluminium bar of these dimensions and a copper bar of these dimensions

Busbar Power Dissipation

The total  Power Dissipated in the busbar is dependent on the resistance of the bar, it's length and the square of the RMS current flowing through it The power dissipated in the busbar is proportional to the square of the current, so if the busbar has a cyclic load, the current should be the RMS current rather than the average. If the maximum current flows for a considerable period of time, this must be used as the current to determine the maximum busbar temperature, but the power dissipation is based on the square root of the maximum current squared times the period for which it flows plus the lower current squared times the period it flows all divided by the square root of the total time. For example, a busbar carries a current of 600 Amps for thirty seconds, then a current of 100 amps for 3000 seconds, then zero current for 3000 seconds. The power dissipation is based on an RMS current of sqrt(600x600x30 + 100x100x3000 + 0 x 3000)/sqrt(30 + 3000 + 3000) = 82.25 Amps.

To calculate the Power Dissipation of a busbar, enter in the width, length and thickness of the bar, and the RMS Current passing through it. Select the units as either metric or imperial. The program displays the Power Dissipated in both an aluminium bar of these dimensions and a copper bar of these dimensions. Enter the ambient temperaturearound the bar in either Celsius or Fahrenheit and the program will check the suitability of the bar for this application.

Busbar Ratings 

Busbar ratings are based on the expected surface temperature rise of the busbar. This is a function of the thermal resistance of the busbar and the power it dissipates. The thermal resistance of the busbar is a function of the surface area of the busbar, the orientation of the busbar, the material from which it is made, and the movement of air around it. The power dissipated by the bus bar is dependent on the square of the current passing through it, its length, and the material from which it is made. Optimal ratings are achieved when the bar runs horizontally with the face of the bar in the vertical plane. i.e. the bar is on its edge. There must be free air circulation around all of the bar in order to afford the maximum cooling to its surface. Restricted airflow around the bar will increase the surface temperature of the bar. If the bar is installed on its side, (largest area to the top) it will run at an elevated temperature and may need considerable derating. The actual derating required depends on the shape of the bar. Busbars with a high ratio between the width and the thickness, are more sensitive to their orientation than busbars that have an almost square cross section. Vertical busbars will run much hotter at the top of the bar than at the bottom, and should be

derated in order to reduce the maximum temperature within allowable limits. Maximum Busbar ratings are not the temperature at which the busbar is expected to fail, rather it is the maximum temperature at which it is considered safe to operate the busbar due to other factors such as the temperature rating of insulation materials which may be in contact with, or close to, the busbar. Busbars which are sleeved in an insulation material such as a heatshrink material, may need to be derated because of the potential aging and premature failure of the insulation material.

The Maximum Current rating of Aluminium Busbars is based on a maximum surface temperature of 90 degrees C (or a 60 degree C temperature rise at an ambient temperature of 30 degrees C). If a lower maximum temperature rating is desired, increase the ambient temperature used for the calculations. i.e. If the actual ambient temperature is 40 degrees C and the desired maximum bar temperature is 80 degrees C, then set the ambient temperature in the calculations to 40 + (90-80) = 50 degrees C. The  Maximum Current rating of Copper Busbars is based on a maximum surface temperature of 105 degrees C (or a 75 degree C temperature rise at an ambient temperature of 30 degrees C).

The  Busbar Width is the distance across the widest side of the busbar, edge to edge.

The Busbar Thickness is the thickness of the material from which the Busbar is fabricated. If the busbar is manufactured from a laminated material, then this is the overall thickness of the bar rather than the thickness of the individual elements. The  Busbar Length is the total length of busbar used.

The  Busbar Current is the maximum continuous current flowing through the busbar. The power dissipated in the busbar is proportional to the square of the current, so if the busbar has a cyclic load, the current should be the RMS current rather than the average. If the maximum current flows for a considerable period of time, this must be used as the current to determine the maximum busbar temperature, but the power dissipation is based on the square root of the maximum current squared times the period for which it flows plus the lower current squared times the period it flows all divided by the square root of the total time. For example, a busbar carries a current of 600 Amps for thirty seconds, then a current of 100 amps for 3000 seconds, then zero current for 3000 seconds. The power dissipation is based on an RMS current of sqrt(600x600x30 + 100x100x3000 + 0 x 3000)/ssqrt30 + 3000 + 3000) = 82.25 Amps.

The  Ambient Temperature is the temperature of the air in contact with the busbar. If the air is in an enclosed space, then the power dissipated by the busbar will cause an increase in the ambient temperature within the enclosure.

To calculate the rating of a busbar, enter in the width and thickness of the bar, and the ambient temperature around the bar. Select the units as either metric or imperial, and the temperature as Celsius or Fahrenheit. The program displays both the current rating of an aluminium bar of these dimensions and a copper bar of these dimensions.

SILICON CONTROLLED RECTIFIER (SCR)

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The Silicon Controlled Rectifier is the most popular of the thyristor family of four layer regenerative devices. It is normally turned on by the application of a gate pulse when a forward bias voltage is present at the main terminals. However, being regenerative or 'latching', it cannot be turned off via the gate terminals specially at the extremely high amplification factor of the gate. There are two main types of SCR's

Converter grade or Phase Control thyristors These devices are the work horses of the Power Electronics. They are turned off by natural (line) commutation and are reverse biased at least for a few milliseconds subsequent to a conduction period. No fast switching feature is desired of these devices. They are available at voltage ratings in excess of 5 KV starting from about 50 V and current ratings of about 5 KA. The largest converters for HVDC transmission are built with series-parallel combination of these devices. Conduction voltages are device voltage rating dependent and range between 1.5 V (600V) to about 3.0 V (+5 KV). These devices are unsuitable for any 'forced-commutated' circuit requiring unwieldy large commutation components.

The dynamic di/dt and dv/dt capabilities of the SCR have vastly improved over the years borrowing emitter shorting and other techniques adopted for the faster variety. The requirement for hard gate drives and di/dt limting inductors have been eliminated in the process.

Inverter grade thyristors: 

Turn-off times of these thyristors range from about 5 to 50 μsecs when hard switched. They are thus called fast or 'inverter grade' SCR's. The SCR's are mainly used in circuits that are operated on DC supplies and no alternating voltage is available to turn them off. Commutation networks have to be added to the basic converter only to turn-off the SCR's. The efficiency, size and weight of these networks are directly related to the turn-off time, tq of the SCR. The commutation circuits utilised resonant networks or charged capacitors. Quite a few commutation networks were designed and some like the McMurray-Bedford became widely accepted

Asymmetrical, light-activated, reverse conducting SCR's Quite a few varieties of the basic SCR have been proposed for specific applications. The Asymmetrical thyristor is convenient when reactive powers are involved and the light activated SCR assists in paralleling or series operation.

control design

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SOLAR PANELS

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Comparison of D.C. and A.C. Transmission

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D.C. transmission

For some years past, the transmission of electric power by d.c. has been receiving the active consideration of engineers due to its numerous advantages

.

Advantages. The high voltage d.c. transmission has the following advantages over high voltage a.c. transmission :

1. It requires only two conductors as compared to three for a.c. transmission.
2. There is no inductance, capacitance, phase displacement and surge problems in d.c. transmission.
3. Due to the absence of inductance, the voltage drop in a d.c. transmission line is less than the a.c. line for the same load and sending end voltage. For this reason, a d.c. transmission line has better voltage regulation.
4. There is no skin effect in a d.c. system. Therefore, entire cross-section of the line conductor is utilized.
5. For the same working voltage, the potential stress on the insulation is less in case of d.c. system than that in a.c. system. Therefore, a d.c. line requires less insulation.
6. A d.c. line has less corona loss and reduced interference with communication circuits.
7. The high voltage d.c. transmission is free from the dielectric losses, particularly in the case of cables.
8. In d.c. transmission, there are no stability problems and synchronizing difficulties.

Disadvantages

1. Electric power cannot be generated at high d.c. voltage due to commutation problems.
2. The d.c. voltage cannot be stepped up for transmission of power at high voltages.
3. The d.c. switches and circuit breakers have their own limitations.

A.C. transmission.

Now-a-days, electrical energy is almost exclusively generated, transmitted and distributed in the form of a.c.

Advantages

1. The power can be generated at high voltages.
2. The maintenance of a.c. sub-stations is easy and cheaper.
3. The a.c. voltage can be stepped up or stepped down by transformers with ease and efficiency. This permits to transmit power at high voltages and distribute it at safe potentials.

Disadvantages

1. An a.c. line requires more copper than a d.c. line.
2. The construction of a.c. transmission line is more complicated than a d.c. transmission line.
3. Due to skin effect in the a.c. system, the effective resistance of the line is increased.
4. An a.c. line has capacitance. Therefore, there is a continuous loss of power due to charging current even when the line is open.

INSULATED GATE BIPOLAR TRANSISTOR (IGBT)

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The Insulated Gate Bipolar Transistor (IGBT) is a minority-carrier device with high input impedance and large bipolar current-carrying capability. Many designers view IGBT as a device with MOS input characteristics and bipolar output characteristic that is a voltage-controlled bipolar device. To make use of the advantages of both Power MOSFET and BJT, the IGBT has been introduced. It’s a functional integration of Power MOSFET and BJT devices in monolithic form. It combines the best attributes of both to achieve optimal device characteristics

The IGBT is suitable for many applications in power electronics, especially in Pulse Width Modulated (PWM) servo and three-phase drives requiring high dynamic range control and low noise. It also can be used in Uninterruptible Power Supplies (UPS), Switched-Mode Power Supplies (SMPS), and other power circuits requiring high switch repetition rates. IGBT improves dynamic performance and efficiency and reduced the level of audible noise. It is equally suitable in resonant-mode converter circuits. Optimized IGBT is available for both low conduction loss and low switching loss.

main advantages of IGBT over a Power MOSFET and a BJT are:

1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced.

2. Low driving power and a simple drive circuit due to the input MOS gate structure. It canbe easily controlled as compared to current controlled devices (thyristor, BJT) in high voltage and high current applications.

3. Wide SOA. It has superior current conduction capability compared with the bipolar transistor. It also has excellent forward and reverse blocking capabilities.

The main drawbacks are:

1. Switching speed is inferior to that of a Power MOSFET and superior to that of a BJT. The collector current tailing due to the minority carrier causes the turnoff speed to be slow

2. There is a possibility of latchup due to the internal PNPN thyristor structure

The IGBT is suitable for scaling up the blocking voltage capability. In case of Power MOSFET, the on-resistance increases sharply with the breakdown voltage due to an increase in the resistively and thickness of the drift region required to support the high operating voltage. For this reason, the development of high current Power MOSFET with high-blocking voltage rating is normally avoided. In contrast, for the IGBT, the drift region resistance is drastically reduced by the high concentration of injected minority carriers during on-state current conduction. The forward drop from the drift region becomes dependent upon its thickness and independent of its original resistivity.

Basic Structure

The basic schematic of a typical N-channel IGBT based upon the DMOS process is This is one of several structures possible for this device. It is evident that the silicon cross-section of an IGBT is almost identical to that of a vertical Power MOSFET except for the P+ injecting layer. It shares similar MOS gate structure and P wells with N+ source regions. The N+ layer at the top is the source or emitter and the P+ layer at the bottom is the drain or collector. It is also feasible to make P-channel IGBTs and for which the doping profile in each layer will be reversed. IGBT has a parasitic thyristor comprising the four-layer NPNP structure. Turn-on of this thyristor is undesirable.

Some IGBTs, manufactured without the N+ buffer layer, are called non-punch through(NPT) IGBTs whereas those with this layer are called punch-through (PT) IGBTs. The presence of this buffer layer can significantly improve the performance of the device if the doping level and thickness of this layer are chosen appropriately. Despite physical similarities, the operation of an IGBT is closer to that of a power BJT than a power MOSFET. It is due to the P+ drain layer (injecting layer) which is responsible for the minority carrier injection into the N--drift region and the resulting conductivity modulation.

Based on the structure, a simple equivalent circuit model of an IGBT can be drawn as It contains MOSFET, JFET, NPN and PNP transistors. The collector of the PNP is connected to the base of the NPN and the collector of the NPN is connected to the base of the PNP through the JFET. The NPN and PNP transistors represent the parasitic thyristor which constitutes a regenerative feedback loop. The resistor RB represents the shorting of the base-emitter of the NPN transistor to ensure that the thyristor does not latch up, which will lead to the IGBT latchup. The JFET represents the constriction of current between any two neighboring IGBT cells. It supports most of the voltage and allows the MOSFET to be a low voltage type and consequently have a low RDS(on) value. A circuit symbol for the IGBT It has three terminals called Collector (C), Gate (G) and Emitter (E).

IXYS has developed both NPT and PT IGBTs. The physical constructions for both of them are As mentioned earlier, the PT structure has an extra buffer layer which performs two main functions: (i) avoids failure by punch-through action because the depletion region expansion at applied high voltage is restricted by this layer, (ii) reduces the tail current during turn-off and shortens the fall time of the IGBT because the holes are injected by the P+ collector partially recombine in this layer. The NPT  IGBTs, which have equal forward and reverse breakdown voltage, are suitable for AC applications. The PT IGBTs, which have less reverse breakdown voltage than the forward breakdown voltage, are applicable for DC circuits where devices are not required to support voltage in the reverse direction.

Operation Modes

Forward-Blocking and Conduction Modes

When a positive voltage is applied across the collector-to-emitter terminal with gate shorted to emitter the device enters into forward blocking mode with junctions J1 and J3 are forward-biased and junction J2 is reverse-biased. A depletion layer extends on both-sides of junction J2 partly into P-base and N-drift region. An IGBT in the forward-blocking state can be transferred to the forward conducting state by removing the gate-emitter shorting and applying a positive voltage of sufficient level to invert the Si below gate in the P base region. This forms a conducting channel which connects the N+ emitter to the N--drift region. Through this channel, electrons are transported from the N+ emitter to the N--drift. This flow of electrons into the N--drift lowers the potential of the N--drift region whereby the P+ collector/ N--drift becomes forward-biased. Under this forward-biased condition, a high density of minority carrier holes is injected into the N--drift from the P+ collector. When the injected carrier concentration is very much larger the background concentration, a condition defined as a plasma of holes builds up in the N--drift region. This plasma of holes attracts electrons from the emitter contact to maintain local charge neutrality. In this manner, approximately equal excess concentrations of holes and electrons are gathered in the N- drift region. This excess electron and hole concentrations drastically enhance the conductivity of N--drift region. This mechanism in rise in conductivity is referred to as the conductivity modulation of the N--drift region.

Reverse-Blocking Mode

When a negative voltage is applied across the collector-to-emitter terminal, the junction J1 becomes reverse-biased and its depletion layer extends into the N--drift region. The break down voltage during the reverse-blocking is determined by an open-base BJT formed by the P+ collector/ N--drift/P-base regions. The device is prone to punch-through if the N--drift region is very lightly-doped. The desired reverse voltage capability can be obtained by optimizing the resistivity and thickness of the N--drift region.