INSTRUMENTATION AND CONTROL APPLICATIONS

   The instrumentation plays an important role in our industry.It helps in precise measurement and testing of a number of quantities of interest.The electronics is also playing an increasingly important role in instrumentation.The cathode ray oscilloscopes (CRO's) frequency counters,signal generators,spectrum analysers,logic analizers,automatic test equipment,vision systems,security surveilance systems digital multimeters (DMM's) power supplies etc.,are some of the instruments,which are found in every industry and research organisations.
  The control industry has improved drastically by the introduction of semiconductor electronics.Devices (discrete as well as integrated circuits,in some traditional areas,such as motor speed control and power rectifiers and inverters,there has been tremendous advancement.Instead of gas filled tubes (thyratrons) we have silicon controlled rectifiers(SCRs),power semiconductor diodes,power bipolar transistors,power MOSFETS,SITS AND IGBT;S.
   Most of the control systems,which are available today,are possible only because of the advances in electronics.Besides analog control systems,we have digital control systems,analog neural network control systems and fuzzy logic control systems.All these systems are in use in digital camcorders,industrial and game robots,factory automation many more.
   The introduction of microprocessors,microcomputers and digital integrated circuits and devices,has led to "smart"instruments and continuously increasing variety of digital control systems.The computers have become integral component of digital control systems.

COMMUNICATION AND ENTERTAINMENT APPLICATIONS

   In the beginning of 20th century,the electronics was used only in the field of telephony and telegraphy.It required a pair of conducting wires.But these days we have cordless telephones,mobile phones which send or receive information without the use of any wire.Such a communication is known as wireless communication.It is possible to have live video conference from anywhere on the earth or in fact millions of kilometers in space.Several space agencies in the world like NASA and ISRO have been using wireless communication on control satallites position controlling digital cameras to take picture and send them back to the earth.
   These days,the radio and television provides a means of communication,education and entertainment.The electronics gadgets like HiFi stereos,CD-player,DVD-player,MP3-player,video games are widely used for entertainment.The use of ICs(integrated circuits)have reduced the size and cost,improved the reliability and performance of the electronic equipment.
   We have the digital cameras and digital camcorders where the picture can be stored on memory stick (flash memory).The picture can be downloaded to a computer to keep a record in albums for sharing with the relatives and friends through the internet.The MP3-player can be used to download the music from the internet and listen at your convenience.

APPLICATIONS OF ELECTRONICS

   These days,we find that the sphere of electronics has spread so vast,that it plays an important role in almost every activity of life.It has penetrated into our homes,our places of work and our means of communication from one place to another.It is believed that by the end of 2025,the electronics will be like the electric motor of today (i.e.,its presence will go unnoticed).Although,electronics has a large number of applications,yet the following are important from the subject point of view:

1. Communication and entertainment applications.
2. Instrumentation and control applications.
3. Defence applivations.
4. Applications in medicine.
5. Computer - aided design of electronic circuits.

  

MODERN TRENDS IN ELECTRONICS

   The development of an integrated circuit (IC) in 1961 wasa great achievement in the field of electronics.But,as there is no end to the man's desire,the growth accelerated further every year.Rapid developments have been made in the integrated circuit technology.Thus starting from the small-scale integration (SSI) in 1961,then medium-scale integration (MSI) in 1966,and large-scale integration (LSI)in 1970.In 2004 we have a very large-scale integration (VLSI) Ultra large -scale integration (ULSI) and Giga-scale integration (GSI).It means that now we have a technology,which can fabricate several million components on a single chip.
   It will be interesting to know that the use of vacuum tube hase become almost obsolete in 1960's.It was replaced by the solid state devices (bipolar transistors and field-effect transistors).Similarly the developments in integrated circuit technology,has made the use of individual transistors as unnecessary.These days,we see all electronic systems made of IC's.The developments which,have taken place in last 60 years,may be understood from the fact that today's microcomputer is several thousand times faster,has a huge memory,million times more reliable,consumes negligible power,occupies 1/100,000 the volume and costs 1/50,000 as compared to the first large electronic computer.
   The microelectronics (term used for the  fabrication of VLSI/ULSI/GSI- circuits)has made a great impact on communication control and computer industries.The applications,which were difficult to realize earlier,have now become possible.In last decade,silicon based technology has dominated the sphere of electronics and will continue to play the role for the next decade as well.However,after that gallium arsenide(Gas) might play a significant role in electronics.

TRACKING WITH RADER

  A tracking-rader system measures the coordinates of a target and provides data which may be used to determine the target path and o predict its future position.All or only part of the available rader data - range,elevation,angle,azimuth angle and doppler frequency shift may be used in predicting future position;that is,a rader might track in range,in angle,in dopple,or with any cobination.Almost any rader can be considered a tracking reder provided its output information is processed properly.But,in general,it is the method by which angle tracking is accomplished that distinguishes what is normally considered a tracking rader and a track-while-scan (TWS) rader.The former supplies continuous tracking data on a particular target,while the track-while-scan supplies sampled data on one or more targets.In generalthe continuous tracking rader and the TWS rader employ different types of equipment.

   The antenna beam in the continuous tracking rader is positioned anle y a aservomechanism actuated by an reeor signal.The various methods for generating the error signal may be classified as sequential lobing,conical scan and simultaneous lobing or monopulse.The range and doppler frequency shift can also be continuously tracked,if desired by a servo-control loop actuated by an error signal generated in the rader receiver.The informatio available from a tracking reder may be presented on a
cathode-ray-tube(CRT) display for action by an operator,or may be supplied to an automatic computer which determines th target path and calculates its probable future course.
   The tracking rader must first find its target before it can track.Some raders operate in a search,or acquisition,mode  in order to find the target before switching to a tracking mode.Although it is possible to use a single rader for both the search and the tracking functions,such a procedure usually results in certain operational limitations.Obviously,when the rader is used in its tracking mode,it has no knowledge of other potential targets.Also,if the antenna pattern is a narrow pencil beam and if the search volume is large,a relatively long time might be required to find the target.Therefore many rader tracking systems employ a separate search rader to provide the information necessary to position the tracker on the target .A search rader,when used for this purpose,it called an acquistion rader.The acquisition rader designates targets to the tracking rader by providing the coordinates where the targets are to be found.The tracking rader acquires a target by performing a limited search in the area of the designated target coordinates.
   The scanning fan-beam search rader can also provide tracking information to determine the path of the target and predict its future position.Each time the rader beam scans path the target,its coordinates are obtained.If the change in target coordinates from scan to scan is not too large,it is possible to reconstruct the track of the target from the sampled data.this may be accomplished by providing the PPI-scope operator with a grease pencil to mark the target pips on the face of the scope.A line joining those pips that correspond to the same target provides the target track.When the trafffic is so dense that operators cannot maintain pace with the information available from the rader,the target trajectory data may be processed automatically in a digital computer.The availability of small,inexpensive minicomputers has made it practical to obtain target tracks,not just target detections,from a surveillance rader.Such processing is usually called ADT(automatic detection and track).When the outputs from more than one rader are automatically combined to provide target tracks,the processing is called ADIT(automatic detection and integrated track) or IADT (integrated ADT).

   A surveillance rader that provides target tracks in sometimes called a track-while-scan rader.This terminology is also applied to raders that scan a limited angular sector to provide tracking information at a high data rate on one or more targets within its field of view.Landing raders used for GCA (ground control of approach) and some missile control raders are of this type.
   When the term tracking rader is used in this book,it generally refers to the continuous tracker,unless otherwise specified.

MODERN TRENDS IN DC TRANSMISSION

MODERN TRENDS IN DC TRANSMISSION

      The continuing technological developments in the areas of power semiconductor devices,digita electronics,adaptive control,Dc protection equipment have increased the pace of applications of Dc transmission.The major contribution of these developments is to reduce the cost of converter stations while improving the reliability and performance.

POWER SEMICONDUCTORS AND VALVES

    The cost of the converters can come down if the number of devices to be connected in series and parallel can be brought down.The size of the devices has gone up to 100 mm (in diameters) and there is no need for parallel connection.The increase in the current rating of the devices has made it possible to provide higher overload capability at reasonable costs and reduce the lower limits on transformer leakage impedance thereby improving the power factor.The voltage ratings are also improve the reliability of converter operation.the cost of the valves is also reduced by the application of zinc oxide gapless arresters and protective firing methods.

   The power rating of thyristors is increased by better cooling methods.Deionized water cooling has now become a standard and results in reduced losses in cooling.Two phase flow using forced vaporization is also being investigated as a means of reducing thermal resistance between the heat sink and the ambient.

   As forced commutated converters operating at high voltages are uneconomic,the development of devices that can be turned off by application of a gate signal would be desirable.Gate turn off (GTO) thyristors are already available 2500 V and 2000 A.However,the main disadvantage of GTo's is the large gate current needed to turn them off.MOS (metal oxide semiconductor) controlled thyristor or MCT appears to be a promising technology.An MCT would consist of an MOS integrated circuit created on the top surface of a high power thyristor.In this device,a very large line current can be switched off by a small gate current.The turn - off time of MCT is also less than one third that of GTOs.however,MCTs are still in the early stages of development.

    The cost of silicon used in the manufacture of power semiconductor devices can be brought down (by 15 to 20 percent) from the use of magnetic CZ (Czochralski) method,instead of the conventional FZ (float zone) method.Research is also underway in reducing this packaging cost of a device.

CONVERTER CONTROL

    The development of micro-computer based converter control equipment has now made in possible to design systems with completely redundant converter control with automatic transfer between systems in the case of a malfunction.not only is the forced outage rate of control equipment reduced but it is also possible to perform scheduled preventive maintenance on the stand - by system when the converter is in operation.The use of a mini - simulator will make it feasible to check vital control and protection functions.

    The micro - computer based control also has the flexibility to try adaptive control algorithms or even the use of expert systems for fault diagnosis and protection.

DC BREAKERS

   With the development and testing of prototype DC breakers,it will be possible to go in for tapping an existing DC link or the development of new MTDC systems.Parallel,rather than series operation of converters is likely as it allows certain flexibility in the planned growth of a system.The DC breaker ratings are not likely to exceed the full load ratings as the control intervention is expected to limit the fault current.

     The control and protection of MTDC systems is not a straightforward extension of that used in the two - terminal DC systems.The possibility of decentralized control necessitated by communication failure,the coordination of control and protection are some of the issues currently being studied.