电器电子专业英文翻译
桂林电子科技大学毕业设计（论文）专用纸第1 页共26页
Preface
During the early years of microprocessors, there were few engineers witheducation and ex perience in the applications of microprocessor technology.Now that microprocessors and m icrocontrollers have become pervasive in somany devices, the ability to use them has bec ome almost a requirement formany technical people.
Today the microprocessor and the microcontroller have become two of themost powerful t ools available to the scientist and engineer. Microcontrollershave been embedded in so ma ny products that it is easy to overlook the factthat they greatly outnumber personal comp uters. Millions of PCs are shippedeach year, but billions of microcontrollers ship annually. While a great deal ofattention is given to personal computers, the vast majority of new designs arefor embedded applications. For every PC designer, there are thousands ofdesign ers using microcontrollers in embedded applications. The number ofembedded designs is g rowing quickly. The purpose of this book is to give thereader the basic design and analy sis skills to design reliable microcontroller ormicroprocessor based systems. The emphasis in this book is on the practicalaspects of interfacing the processor to memory and I/O d evices, and the basicsof interfacing such a device to the outside world.
A major goal of this book is to show how to make devices that are inherentlyreliable by design. While a lot of attention has been given to “quality improve-ment,” the majority of the emphasis has been placed on the processes thatoccur after the design of a product is complete. Design deficiencies are a sig-nificant problem, and can be exceedingly diffi cult to identify in the field.These types of quality problems can be addressed in the desig n phase withrelatively little effort, and with far less expense than will be incurred later i nthe process. Unfortunately, there are many hardware designers and organiza-tions that, fo r various reasons, do not understand the significance and ex-pense of an unreliable design. The design methodology presented in this textis intended to address this problem. Learning to design and develop a microcontroller system without any practicalhands-on ex perience is a bit like trying to learn to ride a bike from readingbook. Thus, another goal is to provide a practical example of a completeworking product. What appears easy on paper may prove extremely difficultwithout some real world experience and some potentia
桂林电子科技大学毕业设计（论文）专用纸第2 页共26页lly painful crashes.
In order to do it right, it’s best to examine and use a real design. On the otherhand, the current state of the technology (surface mounted packaging, etc.)can make the practical s ide problematic. In order to address this problem, aspecial educational System Developme nt Kit is available to accompany thisbook (8031SDK). All the documentation to construct an SDK is availableon the companion CD-ROM. This info, along with updated informati onand application examples, is also available on the web site for this book:http://www.hte. com/echdbook. All the information needed to build the SDKis available there, as well as information on how to order the SDK assembled
and tested.
While searching for an appropriate text for one of the courses I teach inembedded compu ter engineering, I was unable to locate a book that coveredthe topic adequately. An earlie r version of this book was written to accom-pany that course and has since evolved into what you see here. The courseis offered at the University of California, San Diego Exte nded Studies, andis titled “Embedded Controller Hardware Design.” The same courses ma yalso be taken in an on-line format using the Internet, and can be found athttp://www.hte. com/uconline/ecd The goals of the course and the book arevery much the same: to descri be the right way to design embedded systems.
While no prior knowledge of microcontrollers or microprocessors is required,the reader sh ould already be familiar with basic electronics, logic, and basiccomputer organization. Cha pter one is intended as a review of those basicconcepts. Next there is a general overview of microcontroller architecture,and a specific microcontroller chip architecture, the 8051 f amily, is introducedand detailed. The 8051 was chosen because it can be interfaced to ex ternalmemory, has simple timing specs, is widely used and available from a numberof ma nufacturers. The concepts of worst-case design and analysis are describedalong with techni ques for hardware interfacing. A good embedded designrequires familiarity with the underl ying memory technology, including ROM,SRAM, EPROM, Flash EPROM, EEPROM stora ge mechanisms and devices.The processor bus interface is then covered in general form, along with anintroduction to the 8051’s bus interface. Most embedded designs can alsobe
桂林电子科技大学毕业设计（论文）专用纸第3 页共26页nefit from the use of user programmable logic devices (PLD). This subjectis too complex for in-depth coverage here, so PLD technology is covered froma relatively high level. T he central theme of designing an embedded systemthat can be proven to be reliable is ill ustrated with a simple embedded con-troller. The iterative nature of the design process is shown by example, andseveral design alternatives are evaluated. With the central part of the designcompleted, the remaining chapters cover the various types of I/O interfaces,bus operations, and a collection of information that is seldom included in theusual sources, b ut is often handed down from one engineer to another.
I hope that you will find this book to be useful, and welcome any observationsand contri butions you may have. If you should find any errors in the text, or ifyou know of some good embedded design resources, please feel free to contactme directly by e-mail: ken.ar nold@https://www.sodocs.net/doc/7d15428037.html,
CHAPTER ONE
Review of ElectronicsFundamentals
Why are microprocessors and microcontrollers designed into so many differentdevices? W hile there are many dry and practical reasons, I suspect one of thestrongest motivations f or using a microprocessor is simply that it is a lot more fun.Over the past few decades of the so-called “computer revolution,” I have seenmany products and projects that could have been handled without resortingto a microprocessor. Yet there is always a tendency t o rationalize the choice ofa micro-based solution by economic or technical arguments to s upport thedecision. In fact, most of the really excellent products were successful to a gre atextent because they were fun to develop. Many of the best product ideas haveoccurred when someone was “playing” with something they were interestedin. In my own experien ce, I have found learning something new is mucheasier and more effective when I am “j ust playing around” rather than tryingto learn in a structured way or against a deadline. Studies of various educa-tional methods also indicate “coached exploration” is more effect ive than thetraditional methods. These and other observations lead me to the conclusionth at the best way to learn about a microcontroller is by “playing” with one.
No book—no matter how well written—can possibly motivate and educateyou as well as
桂林电子科技大学毕业设计（论文）专用纸第4 页共26页building and playing with a microcontroller. The best way tolearn the concepts in this bo ok is to build a simple microcontroller. Even if itis capable of nothing more than blinkin g a light, it will provide a concreteexample of the microcontroller as a tool that can be f un to use. To ease thiseffort, a companion system development kit (SDK), is available to accompanythis text. It incorporates the functions of a stand-alone single board computer( SBC), and an in-circuit emulator (ICE). It also serves as a sample embeddedcontroller de sign. The design is included on the CD-ROM and web site forthis book, so anyone can reproduce and use it as a learning tool. By applying the guidelines set forth in this book to real world hardware, you can learnto design reliable embedded hardware into other pr oducts. Information onobtaining the SDK can be found in the Preface.
Objectives
Several different skills are required for successful embedded hardware design.Here are so me of the things you will know how to do when you finish this book:
* Interpret design requirements for the design of an embedded controller.
* Read and understand the manufacturer’s specification sheet.
* Select appropriate ICs for the design.
* Interface the CPU, memory, and I/O devices to a common bus.
* Design simple I/O (input/output) interfaces.
* Define the decoding and interconnection of the major components.
* Perform a worst-case analysis of the timing and loading of all signals.
* Understand the software development cycle for a microcontroller.
* Debug and test the hardware and software designs.
These tasks represent the major skills required in the successful applicationof an embedde d micro. In addition, other abilities—such as the design andimplementation of simple user programmable logic—will be covered asrequired to support the proficient application of t he technology.
Embedded Microcomputer Applications
There is an incredible diversity of applications for embedded processors.Most people are aware of the highly visible applications, but there are manyless apparent uses. Many of t
桂林电子科技大学毕业设计（论文）专用纸第5 页共26页he projects my students have chosen turned outto be of practical use in their work. How ever, they have covered the entirerange from the economically practical to the blatantly a bsurd. One practicalexample was the use of a microprocessor to monitor and control the ratio ofingredients used in mixing concrete. About a year after the student imple-mented t he system, he wrote to inform me that the system had saved his com-pany between two and three million dollars a year by reducing the number of “bad batches” of concrete tha t had to be jack hammered out and replaced.
Another example was that of a student who suspended a ball by airflow gener-ated by a fan and provided closed loop control of the ball’s position with themicroprocessor. The only thing that many of the student projects really hadin common was the use of a micr ocontroller as a tool.Some of the actual commercial applications of embedded computer c ontrolsthat the author has been directly involved with include:
* A belt measures a person’s heart rate and respiration that signals an ala rmwhen safe li mits are exceeded. A radio signal is then transmitted to amicrocontroller in a pocket page r to display the type of problem and theidentity of the belt.
* An environmental system controls the heating ventilating and air condi-tioning in one o r more large buildings to minimize peak energy demands.
* A system that measures and controls the process of etching away theunwanted portions of material from the surface of an integrated circuitbeing manufactured.
* The fare collection system used to monitor and control entry to a rapidtransit system b ased on the account balance stored on the magnetic stripeon a card.
* Determination of exact geographic position on the earth by measuring thetime of arriva l of radio signals received from navigational beacons.
* An intelligent phone that receives radio signals from smoke alarms, intru-sion sensors, and panic switches to alert a central monitoring station topotential emergency situations. * A fuel control system that monitors and controls the flow of fuel to aturbine jet engin e.
Selecting a particular processor for a given application is usually a function ofthe designe r’s familiarity with a particular architecture. While there are manyvariations in the details
桂林电子科技大学毕业设计（论文）专用纸第6 页共26页and specific features, there are two general categoriesof devices: microprocessors and mi crocontrollers. The key difference betweena microprocessor and a microcontroller is that a microprocessor contains only amory and I/Oon the chip in addition to a CPU. Microcont rollers are generally used fordedicated tasks. Microcomputer is a general term that applies to complete com-puter systems implemented with either a microprocessor or microcontrol ler.
Microcomputer and Microcontroller Architectures
Microprocessors are generally utilized for relatively high performance appli-cations where cost and size are not critical selection criteria. Because micro-processor chips have their e ntire function dedicated to the CPU and thus haveroom for more circuitry to increase exe cution speed, they can achieve veryhigh-levels of processing power. However, microproces sors require external
memory and I/O hardware. Microprocessor chips are used in desktop PCsand workstations where software compatibility, performance, generality, andflexibility are important.
By contrast, microcontroller chips are usually designed to minimize the totalchip count an d cost by incorporating memory and I/O on the chip. They areoften “application specializ ed” at the expense of flexibility. In some cases, themicrocontroller has enough resources on-chip that it is the only IC requiredfor a product. Examples of a single-chip application include the key fob used toarm a security system, a toaster, or hand-held games. The h ardware interfacesof both devices have much in common, and those of the microcontroller s aregenerally a simplified subset of the microprocessor. The primary design goalsfor each type of chip can be summarized this way:
* microprocessors are most flexible
* microcontrollers are most compact
There are also differences in the basic CPU architectures used, and thesetend to reflect th e application. Microprocessor based machines usually havea von Neumann architecture wit h a single memory for both programs and datato allow maximum flexibility in allocation of memory. Microcontroller chips,on the other hand, frequently embody the Harvard arch itecture, which hasseparate memories for programs and data. Figure 1-1 illustrates this dif
桂林电子科技大学毕业设计（论文）专用纸第7 页共26页ference.
One advantage the Harvard architecture has for embedded applications is dueto the two t ypes of memory used in embedded systems. A fixed program andconstants can be stored in non-volatile ROM memory while working variable data storage can reside in volatile RAM. V olatile memory loses its contentswhen power is removed, but non-volatile ROM memory always maintains itscontents even after power is removed.The Harvard architectur e also has the potential advantage of a separate inter-face allowing twice the memory tra nsfer rate by allowing instruction fetchesto occur in parallel with data transfers. Unfortuna tely, in most Harvard archi-tecture machines, the memory is connected to the CPU using a bus that limitsthe parallelism to a single bus. A typical embedded computer consists of the CPU, memory,and I/O. They are most oftenconnected by means of ashared bus for communication,as shown in Figure 1-2.
桂林电子科技大学毕业设计（论文）专用纸第8 页共26页
The peripherals on a microcon-troller chip are typically timers,counters, serial or parallel data
ports, and analog-to-digital anddigital-to-analog convertersthat are integrated directly onthe chip. The performance ofthese peripherals is generallyless than that of dedicatedperipheral chips, which are frequently used with microprocessor chips. However, having the bus co nnec-tions, CPU, memory, and I/O functions on one chip has several advantages:
* Fewer chips are required since most functions are already present on theprocessor chip. * Lower cost and smaller size result from a simpler design.
* Lower power requirements because on-chip power requirements are muchsmaller than e xternal loads.
* Fewer external connections are required because most are made on-chip,and most of th e chip connections can be used for I/O.
* More pins on the chip are available for user I/O since they aren’t neededfor the bus. * Overall reliability is higher since there are fewer components and interconnections.Of c ourse there are disadvantages too, including:
* Reduced flexibility since you can’t easily change the functions designed into the chip. * Expansion of memory or I/O is limited or impossible.
* Limited data transfer rates due to practical size and speed limits for a single-chip.
* Lower performance I/O because of design compromises to fit everything on one chip.
桂林电子科技大学毕业设计（论文）专用纸第9 页共26页Digital Hardware Concepts
In addition to the CPU, memory, and I/O building blocks, other logic circuitsmay also be equired. Such logic circuits are frequently referred to as glue logicbecause they are used to connect the various building blocks together. The most difficult and important task th e hardware designer faces is the proper selection and specification of this “glue logic.” D evices such as registers,buffers, drivers and decoders are frequently used to adapt the cont rol signals provided by the CPU to those of the other devices. While TTL gate level log ic is still in use for this purpose, the programmable logic device (PLD) has be-come an important device in connecting the building blocks. Contemporary microcontroller designer s need to acquire the following skills:
* Interpretation of manufacturers specifications
* Detailed, worst case timing analysis and design
* Worst case signal loading analysis
* Design of appropriate signal and level conversion circuits
* Component evaluation and selection
* Programmable logic device selection and design
The glue logic used to join the processor, memories, and I/O is ultimately composed of l ogic gates, which are themselves composed almost entirely of transistors, diodes, resistors, and interconnecting wires. In order to under-stand the basic operation of the glue logic, we are going to begin at the com-ponent level with a review of basic electronics concept s. These concepts will
be presented as fluid flow analogies.
V oltage, Current, and Resistance
In Figure 1-3, a battery providesa voltage source for electricity,much like a pump provide s apressure source for a fluid. V oltage,or pressure, is required to producecurrent flow in t he circuit.
桂林电子科技大学毕业设计（论文）专用纸第10 页共26页
The voltage source provides thepressure “motivation,” if you will,for current flow. Resista nce pro-vides a limiting constraint on the amount of current that will actually flow. The resistor will allow a current to flow through it that is proportional to the voltage across i t, and inversely proportional to the resistance value. Higher resistance is like a smaller ap erture for the fluid to flow through. The resistance results in a voltage,or pressure drop, across the resistance as long as current is flowing in the resistor. Figure 1-4 illustrates th is.
桂林电子科技大学毕业设计（论文）专用纸第11 页共26页
The wiring connecting the com-ponents in a circuit is like the piping connecting plumbin g
components that let a fluid flow.The flow of current in the circuit is controlled by the m agnitude of the voltage (pressure) and the resistance(pressure drop) in the circuit. In Figur e 1-5, the battery provides a voltage toforce current through the resistor. The magnitude of the voltage (V) generated by the battery is developed across the resistor, and the mag nitude of the resis-tance (R), determine the current (I). Note the “return”current path i s often shown as “ground,”which is the reference voltage used as the “zero volts”p oint. In this case, current flows from the positive battery terminal, through the wire, then the resistor, then through the “ground”connection to the minus terminal of the batter y. This is usually not the same as earth ground,
which provides a connection to a stake or pipe literally stuck in the ground.The magnitud e of the current in this case is I = V / R by re-arranging the equation V = I * R, as s hown in Figure 1-5. This is known as Ohm’s law.Another way to look at it is that wh enever current flows through a resistor,there is a drop in voltage across the resistor due t o the restriction in current..
桂林电子科技大学毕业设计（论文）专用纸第12 页共26页
their performance in the real world and are subject to other limitations, suchas operating temperature, power limits, etc. Current flows only through acomplete circuit, and in most cases (for a positive power supply) currentflows from the power source through the circ uitry and returns to the powersupply through the common “ground”connection. Current flowing through any resistance results in the dissipation of power as heat. The power di ssiated is P = I^2 R = V*I = V ^2/R. Note that voltage is sometimes denoted by the va riable V and sometimes by E, for electromotive force.
All practical components have some resistance. Real batteries have an internal resistance, for example, which provides an upper limit to the current the battery can supply to an e xternal circuit. Real wires have resistance as well,so the actual performance of a circuit will deviate somewhat from the ideal.These effects are obvious in some cases, but not in others. In an automobile starting circuit, it’s not surprising that the battery, supplying 1 2 volts to a starter with internal resistance on the order of 0.01 to 0.1 ohms, will result in currents of hundreds of amperes in order to start the engine. On the other hand, while consulting with a prominent notebook computer manufacturer,
I uncovered a design error resulting in an internal current of hundreds of amperes flowin g in the circuit for a few nanoseconds. Obviously, this wreaked havoc on the operation o f the computer, and generated a great deal of electro-magnetic noise!
One of the things you will learn in this book is how to avoid those kinds ofmistakes. It ’s also important to remember that power is dissipated in anyresistance present in the ci rcuit. The power is proportional to the voltage times the current across the resistance, wh
桂林电子科技大学毕业设计（论文）专用纸第13 页共26页ich is dissipating the power. In the last two examples, the amount of power dissipated in stantaneously is quite high while the current is flowing. When the current pulse is only a few nanoseconds long,however, it may not be obvious, since there won’t be much heat generated.
Diodes
The diode is a simplesemiconductor device acting as a “one way”current valve. It only lets current flow in one direction. Figure 1-6 illustrates how the diode operates like a “one-way”fluid valve.(Purists please note:This book does not use electron current flow. All electrical current
current)
flow will be “positive”or “conventional”Current flow, meaning
Transistors
The flow analogy can also be used to model how a transistor operates in a logic circuit. The transistor is an amplifier. It uses a small amount of energy to control a larger ener
桂林电子科技大学毕业设计（论文）专用纸第14 页共26页gy source, just as a valve controls a high-pressure water source. There are two kinds of transistors: bipolar and field-effect transistors (FETs).We will look at bipolar transistors fir st; these amplify current. A small amount of current flows in the control circuit (the tran sistor base-emitter circuit) to turn the tran-sistor on. This control current is amplified (mu ltiplied by the gain or beta of the transistor) and allows a larger current to flow in the o utput circuit (the collector-emitter circuit). Once again, the device is not perfect because o f the resistance, current, gain, and leakage limitations of real transistors. Bipolar transistor s come in two polari-ties, NPN and PNP, with the difference being the direction in whic h current flows for normal operation. A bipolar PNP transistor is shown and modeled in Figure 1-7.
Mechanical Switches
Mechanical switches are useful for direct input to digital circuits. One of themore conven ient versions is a bank of rocker switches packaged into a modulethat can fit into the sa me location as a standard chip. The dual in-line package, or DIP, switch is one of the e asiest ways to add multiple switches to a micro-controller design. The mechanical switch has extremely low “on”Resistance and high “off”resistance, unlike most semicondu ctor switches. Figure 1-9shows a typical DIP switch and the schematic symbol for it.
桂林电子科技大学毕业设计（论文）专用纸第15 页共26页
Transistor Switch ON
Transistors can be configured to function as switches. As can be seen in Figure 1-10, an NPN transistor operating as a current controlled switch can be used to build a simple in verter. It changes a logic one on its input to a logic zero at its output, and vice versa. I n this case, logic one is represented as a positive voltage, and a logic zero is represented by zero volts. The logic one
input (positive input voltage) is supplied through a resistor from the power supply voltag
base.
e to the transistor base terminal, resulting in a small base control current into the
The transistor is used because it has gain allowing a larger output current to flow as con trolled by a weaker input. When the transistor is turned on as much as it can be, the co llector emitter circuit looks almost like a short circuit, effectively connecting the output t o ground or zero volts. This gives a logic zero on the collector output. When the transist
桂林电子科技大学毕业设计（论文）专用纸第16 页共26页or collector is shorted to ground, current flows from the supply through the resistor and i nto the transistor collector to ground. The transistor is said to sink the resistor current int o ground. If there is an external load, such as another inverter or gate, connected to the collector output, the transistor can also sink current from the load. This is also referred t o as pulling down the output voltage. The current sinking capacity of the transistor limits the number of devices this inverter can drive.
Transistor Switch OFF
When the input is connected to logic zero (ground voltage), no current flows into the ba se of the transistor, since its base and emitter terminals are at the same voltage. When th ere is no current flowing in the base, the transistor will not allow current to flow in the collector emitter circuit either. As a result, the circuit behaves as if the transistor was re moved from the circuit. The output
resistor will source current to any potential load. The output is pulled up to the supply v oltage, resulting in a logic one at the output. Once again, there is a limit to the resistor ’s ability to source current, resulting in a limit to the number of loads that can be atta ched to this circuit’s output. Notice these two limits are defined by the ability of the tr ansistor to pull down the output, and
the resistor’s ability to pull up the output become the main limits to its ability to drive other devices. Gates can be constructed by adding diodes or transis-tors to the inverter c ircuit in Figure 1-11.
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The FET as a Logic Switch
Most of the logic devices used in highly integrated circuits do not use bipolar tran-sistors. Instead, they use field effect transistors. FETs perform a similar function to the bipolar t ransistors discussed earlier, but they are voltage controlled. While the current flowing in t he base controls bipolar transistors, the voltage between the gate and source controls field effect transistors. The gate voltage of a field effect transistor controls the current flowin g in the drain-source circuit. The
symbol for the FET shows the gate to be insulated from the source-drain circuit, as sho wn in Figure 1-12.
This type of FET is referred to as a MOSFET (metal oxide semiconductor FET),since th e insulating material is silicon dioxide (SiO2 ), commonly known as glass (for early devi ces, the gate was made of metal). Like bipolar NPN and PNP transistors with opposite p
桂林电子科技大学毕业设计（论文）专用纸第18 页共26页olarity, FET come in N- and P- channel varieties.The N- and P- channels refer to the po larity of the source drain element of the device. A cross-section view of a FET is shown in Figure 1-13.
NMOS Logic
The conductive state of the FET’s channel is what allows or prevents current from flow ing in the device. For a typical logic N-channel MOSFET, the channel becomes conducti ve when the gate has a positive voltage with respect to the source, allowing current to fl ow between the drain and source terminals. When the gate is at the same voltage as the source, no current flows. The design of MOS logic circuits can be almost exactly equiv alent to the bipolar inverter we saw earlier, substituting an N-channel MOSFET for the b ipolar NPN transis-tor. In fact, the most of the early microcontroller integrated circuits w ere manufactured using variations of this method, and are referred to as NMOS logic. As can be seen from Figure 1-14, the NMOS FET circuit behaves in an
equivalent way to the NPN transistor inverter. When the gate (control input)of the NMOS FET is at a positive voltage, the FET is ON, effectively shorting the source and drain p ins. When the gate is at 0 volts, the FET is OFF, open-ing the circuit between the sourc e and drain. Older NMOS logic ICs use this type of circuit. The original 8051 microcont roller was an NMOS
processor.
CMOS Logic
CMOS logic (complementary symmetry MOS) is another form of MOS logic.It has advan tages over NMOS logic for low power circuitry and for very complex integrated circuits.
桂林电子科技大学毕业设计（论文）专用纸第19 页共26页NMOS logic is relatively simple, but it has one serious draw-back: it consumes a signifi cant amount of power. In fact, it would be impossible to manufacture the largest ICs usi ng NMOS logic, as the power dissipated by the chip would cause it to overheat. This is the main reason CMOS logic has become the dominant form of logic used for large, co mplex ICs. Instead of using a resistor to source current when the output is high, a CMO S device uses a P-channel MOSFET to pull the output high. CMOS logic is based on th e use of two complementary FETs that switch the output between the
1-15.
power supply and ground. A simple CMOS inverter is shown in Figure
When the transistor gate inputs are at logic one (positive voltage), the P-channel device i s off, and the N-channel device is on, effectively connecting the output to ground, or log ic zero. Likewise, when the input is grounded, the P-channel device turns on and the N-channel device turns off, effectively connecting the output to the positive supply voltage, or logic one. Gates and more complex logic functions can be constructed by using series and parallel-connected MOSFETs in circuits similar to the one above. The gate of a M OSFET, as implied by the symbol, is essentially an open circuit. In fact, the gate of a MOSFET does have an extremely high resistance. The operation of the MOSFET’s chan nel is controlled by the voltage of the gate, unlike the bipolar NPN transistor we examin ed in the inverter, which is controlled by input (base) current. Bipolar transistors are curr ent amplifiers, with their output current being controlled by their base current. FET outpu ts, on the other hand, are dependent on the gate voltage.
桂林电子科技大学毕业设计（论文）专用纸第20 页共26页Since almost no current flows in a CMOS output when it is driving a CMOS gate input in the steady state condition, these logic devices consume much less power than the oth er types. MOS logic has some other advantages over bipolar logic, since there is almost no input current (less than one nanoampere,or 10 ^-9 ampere), so it does not need to ex act a DC current load on the device
driving it. This is good news, because it means that the input current of a CMOS device does not limit the number of gates that can be connected to the output of the driving g ate. The number of gate inputs that a single gate output can drive is the gate fan-out. Fa n-out applies between gates of the same logic family, as different families of logic have different output capabilities and their
inputs present different loads.
Now for the bad news about the high input resistance of MOS devices: theinsulation sep arating the input from the channel is very thin (measured in angstroms). This thin layer can easily be punctured by electrostatic discharge (ESD), such as occurs regularly when d issimilar materials rub against one another. Just walking across the room can generate ten s of kilovolts, which is more than enough to destroy a MOS device. As a result, special precautions must be taken to prevent damage to MOS devices. When handling these dev ices, it is important to ground your body before touching the device, and to also keep th e device at or near ground. Special wrist straps and workspace mats are available to assi st in keeping static voltages from building up and for dissipating them when they do occ ur. Special, conductive bags and containers should be used when possible to contain sensi tive devices.
CMOS power consumption is usually dominated by the power consumed dur-ing the trans ition of a logic device from one state to another. As a result, pure CMOS devices consu me only a few microamperes of current when they are not switching, and the bulk of th e current drawn is a function of clock frequency. The higher the clock frequency, the gre ater the current consumption. For pure CMOS, the power supply current is linearly propo rtional to the clock rate.
Mixed MOS
电气工程及其自动化专业英语(1)重点
电气工程及其自动化专业英语 考试题型：选择10*2 单词翻译10*2 短句翻译5*4 长句翻译4*10 Exercise All the simple circuit elements that will be 在下面进行的工作中我们要研究的简单电路元件,可以根据流过元件的电流与元件两端的电压的关系进行分类。例如，如果元件两端的电压正比于流过元件的电流，即u＝ki，我们就把元件称为电阻器。其他的类型的简单电路元件的端电压正比于电流对时间的导数或正比于电流关于时间的积分。还有一些元件的电压完全独立于电流或电流完全独立于电压，这些是独立源。此外，我们还要定义一些特殊类型的电源，这些电源的电压或电流取决于电路中其他的电流或电压，这样的电源将被称为非独立源或受控源。 It must be emphasized that the linear 必须强调的是线性电阻器是一个理想的电路元件；它是物理元件的数学模型。我们可以很容易地买到或制造电阻器，但很快我们发现这种物理元件只有当电流、电压或者功率处于特定范围时其电压——电流之比才是恒定的，并且这个比值也取决于温度以及其它环境因素。我们通常应当把线性电阻器仅仅称为电阻器。只有当需要强调元件性质的时候才使用更长的形式称呼它。而对于任何非线性电阻器我们应当始终这么称呼它，非线性电阻器不应当必然地被视为不需要的元件。 If a circuit has two or more independent 如果一个电路有两个或多个独立源，求出具体变量值（电流或电压）的一种方法是使用节点分析法或网孔分析法。另一种方法是求出每个独立源对变量的作用然后把它们进行叠加。而这种方法被称为叠加法。叠加法原理表明线性电路某个元件两端的电压（或流过元件的电流）等于每个独立源单独作用时该元件两端的电压（或流过元件的电流）的代数和。 The ratio of the phase voltage to the 相电压与相电流之比等于电路的阻抗，符号为字母Z，阻抗是一个具有量纲为欧姆的复数量。阻抗不是一个相量，因此不能通过把它乘以e jωt,并取其实部把它转换成时域形式。但是，我们把电感器看作是通过其电感量L表现为时域形式而通过其阻抗jωL表现为频域形式，电容在时域里为电容量C而在频域里为1/jωc，阻抗是某种程度 上的频域变量而非时域变量。 Both wye and delta source connections 无论是星型连接的电源还是三角形连接的电源都有重要的实际应用意义。星型连接的电源用于长距离电力传输，此时电阻损耗(I2R)将达到最小。这是由于星型连接的线电压是三角形连接的线电压的√3倍，于是,对于相同的功率来说，三角型连接的线电流是星形连接的线电流的√3倍。三角形连接的电源使用在根据三相电源而需要的三个单相电路中。这种从三相到单相的转变用在住宅布线中因为家用照明和设备使用单相电源。三相电源用在需要大功率的工业布线中。在某些应用场合，无论负载是星形连接还是三角形连接并不重要。
电气英语翻译
Heat sink 散热器 Forward conduction 正向导通 Thyristor 晶闸管 Solid-state power device 固态功率器件 Silicon wafer 硅片，硅晶片 Self-latching 自锁 电流额定值current rating 反向击穿电压reverse breakdown voltage 负电流脉冲negative current pulse 交流电动机相位控制phase control AC motor 反向并联二极管reverse shunting diode 正信号positive signal Gate-turn-off thyristors 可关断晶闸管 固态功率器件基础 2.1 引言 在这一章中我们重点讨论固态功率器件，并且只讨论它们在相位控制或频率控制的三相460V交流鼠笼式感应电动机的应用。 2.2 固态功率器件 应用于固态交流电动机控制的功率半导体主要的五个类型如下： （1）二极管 （2）晶闸管（例如：硅控整流器SCRs） （3）（电子）晶体管 （4）可关断晶闸管 （5）双向可控硅 硅控整流器和双向可控硅通常用于相位控制。各种各样的二极管制品、硅控整流器、电子晶体管和可开断晶体管都应用于速度控制。这些器件的共性是：利用硅晶体薄片层层堆叠构成PN结的各种组合。在二极管、硅控整流器和可关断晶闸管中，P结常被叫作阳极，N结常被叫做阴极，在电子晶体管中相应的被叫做集电极和发射极。这些器件的区别在于导通和关断的方法及电流和电压的容量。 让我们来简答看一下这些器件，了解一下他们的参数。 2.2.1 二极管 图2.1是一个二极管。左边是一个中间有硅晶片的PN结，右边是单个二极管的表示符号。当阳极为正阴极为负时，会有电流通过，二极管本身伴随着一个比较小的压降。当极性相反时，只有很小的反向漏电流通过，这在图2.2中有表现出来。正向压降一般是1V左右，与电流额定值无关。 （PN结阳极阴极单个二极管PN结和表示符号） 二极管的正向电流额定值取决于起大小和设计，而这二者是根据器件的散热要求来确定的，一保证掐进不超过最大结温（通常是200℃）。 反向击穿电压（见图2.2）是二极管的另一个重要参数，它的数值较二极管尺寸大小更多地取决于其内部设计。
广告英语翻译常用词语
广告英语翻译常用词汇 产品远销英国、美国、日本、意大利和东南亚，深受消费者欢迎和好评Our products are sold in Britain, America, Japan, Italy and South East Asia and well appreciated by their purchasers. 畅销全球 selling well all over the world 典雅大方 elegant and graceful 定型耐久 durable modeling 方便顾客 making things convenient for customers 方便群众 making things convenient for the people; to suit the peo ple's convenience 方便商品 convenience goods 方便生活 bringing more convenience to the people in their daily life; prov iding amenities for the people; making life easier for the popula tion 各式俱全 wide selection; large assortment
顾客第一 Customers first 顾客是我们的皇帝 We take customers as our Gods. 规格齐全 a complete range of specifications; complete in specific ations 花样繁多 a wide selection of colours and designs 货色齐全 goods of every description are available. 客商第一，信誉第一 clients first, reputation first 款式多样 a great variety of models 款式活泼端庄 vivid and great in style 款式齐全 various styles 款式新颖 attractive designs; fashionable(in) style; novel (in) de sign; up-to-date styling 款式新颖众多 diversified latest designs 美观大方 elegant appearance 美观耐用 attractive and durable 品质优良，疗效显著，誉满全球，欢迎选购 excellent quality, evident effect, good reputation over the world, orders are welcome. 品种多样 numerous in variety 品种繁多 great varieties 品种齐全 complete range of articles; a great variety of goods
电气英文文献+翻译
POWER SUPPLY AND DISTRIBUTION SYSTEM ABSTRACT The basic function of the electric power system is to transport the electric power towards customers. The l0kV electric distribution net is a key point that connects the power supply with the electricity using on the industry, business and daily-life. For the electric power, allcostumers expect to pay the lowest price for the highest reliability, but don't consider that it's self-contradictory in the co-existence of economy and reliable.To improve the reliability of the power supply network, we must increase the investment cost of the network construction But, if the cost that improve the reliability of the network construction, but the investment on this kind of construction would be worthless if the reducing loss is on the power-off is less than the increasing investment on improving the reliability .Thus we find out a balance point to make the most economic,between the investment and the loss by calculating the investment on power net and the loss brought from power-off. KEYWARDS：power supply and distribution,power distribution reliability，reactive compensation,load distribution
常用专业术语翻译
1.素质教育：Quality Education 2. EQ：分两种，一种为教育商数Educational quotient，另一种情感商数Emotional quotient 3. 保险业：the insurance industry 4. 保证重点指出：ensure funding for priority areas 5. 补发拖欠的养老金：clear up pension payments in arrears 6. 不良贷款：non-performing loan 7. 层层转包和违法分包：mutlti-level contracting and illegal subcontracting 8. 城乡信用社：credit cooperative in both urban and rural areas 9. 城镇居民最低生活保障：a minimum standard of living for city residents 10. 城镇职工医疗保障制度：the system of medical insurance for urban workers 11. 出口信贷：export credit 12. 贷款质量：loan quality 13. 贷款质量五级分类办法：the five-category assets classification for bank loans 14. 防范和化解金融风险：take precautions against and reduce financial risks 15. 防洪工程：flood-prevention project 16. 非法外汇交易：illegal foreign exchange transaction 17. 非贸易收汇：foreign exchange earnings through nontrade channels 18. 非银行金融机构：non-bank financial institutions 19. 费改税：transform administrative fees into taxes 20. 跟踪审计：foolow-up auditing 21. 工程监理制度：the monitoring system for projects 22. 国有资产安全：the safety of state-owned assets 23. 过度开垦：excess reclamation 24. 合同管理制度：the contract system for governing projects 25. 积极的财政政策：pro-active fiscal policy 26. 基本生活费：basic allowance 27. 解除劳动关系：sever labor relation 28. 金融监管责任制：the responsibility system for financial supervision 29. 经济安全：economic security 30. 靠扩大财政赤字搞建设：to increase the deficit to spend more on development 31. 扩大国内需求：the expansion of domestic demand 32. 拉动经济增长：fuel economic growth 33. 粮食仓库：grain depot 34. 粮食收购企业：grain collection and storage enterprise 35. 粮食收购资金实行封闭运行：closed operation of grain purchase funds 36. 粮食销售市场：grain sales market 37. 劣质工程：shoddy engineering
电气专业英语翻译
Foundation of PLC 1. The central processing unit Although referred to as the brain of the system, the Central Processing Unit in a normal installation is the unsung hero, buried in a control cabinet, all but forgotten. 2. Basic Functionality In a programmable controller system, the central processing unit(CPU) provides both the heart and the brain required for successful and timely control execution. It rapidly and efficiently scans all of the system inputs, examines and solves the application logic, and updates all of the system outputs. In addition, it also gives itself a checkup each scan to ensure that its structure is still intact. In this chapter we will examine the central processing unit as it relates to the entire system. Included will be the various functional blocks in the CPU, typical scan techniques, I/O interface and memory users, power supplies, and system diagnostics. 3. Typical Function Block Interactions In practice, the central processing unit can vary in its architecture, but consists of the basic building block structure illustrated in Fig.1.1.The processing section consists of one or more microprocessors and their associated circuitry. While it is true that some of the luxury of using microprocessors, most modern systems use either a single microprocessors such as the AMD 2903, usedin a bit slice architecture. This multiple microprocessor system to break the control system tasks into many small components which can be executed in parallel. The result of this approach is to achieve execution speeds that are orders of magnitude faster than their single-tasking counterparts. In addition to efficiently processing direct I/O control information and being programmable, the real advantage that microprocessor-based system have over their hardwired relay counterparts is the ability to acquire and manipulate numerical data easily. It is this attribute that makes programmable controllers the powerhouses that they are today in solving tough factory automation problems. The factory of tomorrow will run efficiently only if quality information about process needs and status of the process equipment are known on a realtimes basis. This can and will come about only if the unit level controllers, including programmable controllers, are empowered with the ability to collect, analyze, concentrate, and deliver data about the process. As the
翻译常用词汇
翻译常用词汇 高枕无忧resting without worries 史无前例unprecedented in the history 不可一世a conquering hero 毫不示弱equally firmly 量体裁衣to act according to actual circumstances 一刀两断to cut it clean 与虎谋皮to ask a tiger for its skin 六亲不认to disown all one’s relatives and fri ends 英雄本色the true quality of a hero 英雄所见略同Great minds think alike. 每逢佳节倍思亲On festive occasions more than ever we think of our dear ones faraway. 上有好，下必有其焉。What the superior loves, his inferiors will be found to love exceedingly.大江东去，浪淘尽，千古风流人物。The Great River flows to the east: Its waves have washed away all the men of untrammeled spirit of a thousand ages. 上兵伐谋，其次伐交。What is supremely important in war is to attack the enemy’s strategy. Next best is to disrupt his alliances. 问君能有几多愁，恰似一江春水向东流。I wonder how many sorrows you have. They are exactly like the Yangtze River unceasingly flowing eastward in spring. 千呼万唤始出来，犹抱琵琶半遮面。Only after a thousand entreaties does she appear. Her face half hidden behind the guitar (pipa) in her arms. 吃得苦中苦，方为人上人。Only if you can stand the hardest of hardships can you hope to rise in society. 是非经过不知难You never know how hard a task is almost until you have done it yourself. 满招损Pride goes before a fall. / Pride spells failure. 适可而止Bind the sack before it be full. 好汉做事好汉当A true man has the courage to accept the consequences of his own actions.知己知彼，百战不殆。To know one’s and the enemy’s situation ensures victory. 牵扯之覆，后车之鉴。The overturned car ahead is a warning to the ones behind. 山雨欲来风满楼The wind sweeping through the tower heralds a rising storm in the mountains. 是故学然后知不足，教然后之困。Therefore, to learn makes us realize our deficiency, and to teach makes us know the difficulties. 人尽其才、地尽其利、物尽其利、货畅其流。Our human, land and material resources should be used to the best advantage, and our goods should be in good circulation. 父母有抚养教育未成年子女的义务，成年子女有赡养扶助父母的义务。Parents have the duty to rear and education their children who are minors, and children who have come of age have the duty to support and assist their parents. 中华人民共和国公民有劳动的权利和义务。Citizens of the P eople’s Republic of China have the right as well as the duty of work. 各民族公民都有用本民族语言文字进行诉讼的权利。Citizens of all nationalities have the right to use the spoken and written languages of their own nationalities in court proceedings.
电气专业术语中英对照
一．电气名词Electric items 二．线路（母线、回路）Lines (Bus , circuits) 三．设备Equipments 四．保护、继电器Protection , relays 五．电气仪表Electric instruments 六．防雷Lightning protection 七．接地Grounding , earthing 八．室、所Room , Substation 九．电修车间设备Equipments of electric repair 十．材料Material 十一．图名Drawings , diagrams 十二．表头Tables 十三．标准图词汇Terms from standard DWG 一．电气名词Electric items 交（直）流Alternating (direct) current 短路电流Short-circuit current 起始次暂态短路电流Initial subtransient short-circuit current 冲击电流Impulse current 稳态短路电流Steady state short-circuit current 临界电流Critical current 切断电流Rupturing current 熔断电流Blow-out current 故障电流Fault current 计算电流Calculating current 极限有限电流Limit effective current 过电流Over current 逆电流Inverse current 整定电流Setting current 额定电流Rated current 电流密度Current density 短路电流最大有效值Maximum effective value of short-circuit current 高压High-voltage , High-tension 低压Low-voltage , Low-tension 计算电压Calculating voltage 激磁电压Exciting voltage 冲击电压Impulse voltage 临界电压Critical voltage
建筑电气英文翻译
建筑电气 电气工程设计包括两个主要的设计方面。主要是一部分的电能的转换及分配和电力的供配、照明系统、防雷接地系统。一般来说,建筑主要的变化包括:高压和低压配电系统、变压器、备用电源系统。电力系统包括配电和控制，室内和室外照明系统包括所有类型的照明，防雷系统包括入侵波防护、闪电传感器、接地、等电位连接和局部等电位连接等。辅助等电位连接等。在短短的20年里,系统在技术和产品的面貌发生了翻天覆地的变化。许多的设计理念也发生了巨大的变化。开关设备如高压系统的第一个断路器油断路器，后来油断路器的逐步发展,不仅规模大,但是一般都包含油物质。由于开关设备尺寸较大,我们还必须建立独立的设备房间,占据了大量的建筑面积。现在真空断路器和六氟化硫断路器,不仅体积小,而且短路容量大，外壳尺寸远小于原来的橱柜，并且断路器没有任何油,防火性能大大提高。而且断路器和其他低压设备在一个房间里,这样即节省空间又方便管理。过去大容量的低压断路器,短路电流容量逐渐变大,规模也逐渐变小,而且更加稳定,使系统运行更加安全可靠,为设计带来了方便。向着智能化低压断路器方向发展,断路器各种参数可以通过总线工业控制,信号直接传输到计算机。 干式变压器的出现,对建筑电气设计带来了极大的方便,因为没有变压器油泄漏和火灾的可能性,以便它可以很容易地安装在建筑本身,甚至直接到负荷中心。它还消除变压器对油的需求限制,构建大容量设备时可以使用干式变压器。在实际工程设计中曾应用四个台湾2500kVA干式变压器。 在使用紧急发电机方面,从性能和尺寸的角度来看,比过去进步很多。除了使用柴油发电机；应急照明使用EPS备用电源；中断供电在一个毫秒以内的设备,可以使用UPS。 电力设备的控制从单一元件的控制到控制继电器控制变化。除了更好的性能的各种组件的规模较小,也降低控制箱的规模。由于数字技术更多的运用于控制能达到最佳的控制状态来控制设备。进一步提高了节能的效果。 照明系统从过去单一光源、灯具和低效率的状态向更广泛的前景发展。建筑中使用的光源可供选择的品种数量很多。光的发光效率和色调在向着高效的方向发展,灯具不断地改进其效率和不同形式的灯具运用于不同场合。例如,普通的荧光灯镇流器由普通的镇流器向节能型镇流器方向发展。还对谐波组件的大小进行精简,生产低谐波电子镇流器。许多措施如配件和灯具的使用,可以满足设计要求,同时能实现不同的体系结构、照明要求的各种场所。无论照明和室内装饰照明还是道路照明和户外庭院建筑的光照明,所有的都展示了照明技术的发展和建筑照明的好处与便利。
2019英语四级翻译常用词汇：教育词汇
2019英语四级翻译常用词汇：教育词汇 成人夜校 night school for adults 在职进修班 on-job training courses 政治思想教育 political and ideological education 毕业生分酉己 graduate placement; assignment of graduate 充电update one’s knowledge 初等教育 elementary education 大学城 college town 大学社区 college community 高等教育 higher education 高等教育“211 工程” the “211 Project” for higher education 高等学府 institution of higher education 综合性大学 comprehensive university 文科院校 colleges of (liberal) arts 理工科大学 college / university of science and engineering 师范学院teachers’ college; normal college 高分低能 high scores and low abilities 高考(university/college) entrance examination 高校扩招 the college expansion plan
教育界 education circle 教育投入 input in education 九年义务教育 nine-year compulsory education 考研 take the entrance exams for postgraduate schools 课外活动 extracurricular activities 必修课 required/compulsory course 选修课 elective/optional course 基础课 basic courses 专业课 specialized courses 课程表 school schedule 教学大纲 teaching program; syllabus 学习年限 period of schooling 学历 record of formal schooling 学分 credit 启发式教学 heuristic teaching 人才交流 talent exchange 人才战 competition for talented people 商务英语证书 Business English Certificate (BEC) 适龄儿重入学率 enrollment rate for children of school age 升学率 proportion of students entering schools of a higher grade; enrollment rate
电气工程专业英语翻译
实用资料：电气工程专业课(电力类)翻译参考 专业外语：Professional English 电路（上） electrical circuit (I) 电路（下） electrical circuit (II) 金工实习 machinery practice 电机（上） electrical machinery (I) 电工实验与测试 electrical experiment & test 电子综合实践 integrated electronic practice 信号与系统 signal & system 电子技术基础（模拟） fundamentals of electronic (analog) 电磁场electromagnetic field 电子技术实验 electronic experiment(I) 电子辅助设计EDA Electronic Design Automatic(I) 发电厂动力工程基础 Heat power engineering in generating plant 企业管理 enterprise management 电气主系统electrical system principle 电力系统稳态/暂态分析 Steady-State/ Transient-State Analysis of Power System 电力系统继电保护 Power System Relaying Protection 电力系统潮流计算机分析：Computer Analysis of Power Flow 数字电子技术 Digital Electrical Technique 微机原理 microcomputer principle 电子技术基础（数字） fundamentals of electronic (digital) 自动控制 automatic control theory 电力系统分析 electric power system analysis 电子技术基础实验electronic experiment(II) 电气主系统课程设计 electrical system principle-course design 电子辅助设计EDA Electronic Design Automatic(II) 通信与计算机网络 communication & computer networks 电力系统继电保护 electric power system relaying 电力系统继电保护 Power System Protective Relaying 电力系统远动技术electric power system remote protocol 生产实习productive practice Technology 继电保护课程设计 electric power system relaying-course design 电力电子技术 power electronics 电力电子技术基础：Fundamentals of Electronics Power Technology 电力电子课程设计 Power electronics course design 电力系统自动控制 electric power system control & automation 高电压技术 High voltage engineering Technology 变电站自动化 substation automation 电力经济 electric power system economics 电能质量控制 electric power quality control 配电网自动化 distribution system automation 电力系统新技术 new techniques on electric power system
电气专业术语中英文对照
一．电气名词 Electric items 二．线路（母线、回路）Lines (Bus , circuits) 三．设备 Equipments 四．保护、继电器 Protection , relays 五．电气仪表 Electric instruments 六．防雷 Lightning protection 七．接地 Grounding , earthing 八．室、所 Room , Substation 九．电修车间设备 Equipments of electric repair 十．材料 Material 十一．图名 Drawings , diagrams 十二．表头 Tables 十三．标准图词汇 Terms from standard DWG 一．电气名词 Electric items 交（直）流 Alternating (direct) current 短路电流 Short-circuit current 起始次暂态短路电流 Initial subtransient short-circuit current 冲击电流 Impulse current 稳态短路电流 Steady state short-circuit current 临界电流 Critical current 切断电流 Rupturing current 熔断电流 Blow-out current 故障电流 Fault current 计算电流 Calculating current 极限有限电流 Limit effective current 过电流 Over current 逆电流 Inverse current 整定电流 Setting current 额定电流 Rated current 电流密度 Current density 短路电流最大有效值 Maximum effective value of short-circuit current 高压 High-voltage , High-tension 低压 Low-voltage , Low-tension 计算电压 Calculating voltage 激磁电压 Exciting voltage 冲击电压 Impulse voltage 临界电压 Critical voltage 残留电压 Residual voltage 击穿电压 Puncture voltage 脉动电压 Pulsating voltage 供电电压 Supply voltage 电力电压 Power voltage
电脑与信息专业技术英语翻译常用专业词汇
这里汇聚了计算机和网络技术领域的大部分英语词汇和详细解说，如果要查询相关词汇，你可以点此word文档工具栏的“编辑”，找到“查找”，然后点开输入你要查询的词汇就可以查询了。 A AAIMS（An Analytical Information Management System）分析信息管理系统 Abacus 算盘 Access security 存取安全 Access time 存取时间 Active 有源的 Ada programming language Ada 程序设计语言 Adapter 适配器 Adapter card 转接卡 Add-on 外接式附件 Address 地址 ADSL(Asymmetric Digital Subscriber Line) 非对称数字客户线路 After-image record 残留影像记录 Algorithm 算法 Alpha testing ɑ测试 3 Alteration switch 变换开关 ALU(Arithmetic/Logic Unit)运算器 Amplitude 幅度 Analog data 模拟数据 Analog cellular 模拟移动电话 Analog signal 模拟信号 Analysis block 分析块 Animation 动画制作 ANSL(American National Standards Label)美国国家标准标号 Answerback memory 应答存储器 Anti-noise coding 反噪声编码 Antivirus software 反病毒软件 APL(A Programming Language) APL 语言 Application development cycle 应用开发周期 Application program 应用程序 4 Application software 应用软件 Arithmetic operation 算术运算 ARP(Automatic Receive Program)自动接受程序 Artificial network 仿真网络 ASCII(American standard Code for Information Interchange)美国信息交 换用标准代码 Assembler 汇编程序 Assembly language 汇编语言 Asynchronous 异步的
电气自动化专业毕业论文英文翻译
电厂蒸汽动力的基础和使用 1.1 为何需要了解蒸汽 对于目前为止最大的发电工业部门来说, 蒸汽动力是最为基础性的。 若没有蒸汽动力, 社会的样子将会变得和现在大为不同。我们将不得已的去依靠水力发电厂、风车、电池、太阳能蓄电池和燃料电池,这些方法只能为我们平日用电提供很小的一部分。 蒸汽是很重要的,产生和使用蒸汽的安全与效率取决于怎样控制和应用仪表,在术语中通常被简写成C&I(控制和仪表 。此书旨在在发电厂的工程规程和电子学、仪器仪表以 及控制工程之间架设一座桥梁。 作为开篇,我将在本章大体描述由水到蒸汽的形态变化,然后将叙述蒸汽产生和使用的基本原则的概述。这看似简单的课题实际上却极为复杂。这里, 我们有必要做一个概述:这本书不是内容详尽的论文,有的时候甚至会掩盖一些细节, 而这些细节将会使热力学家 和燃烧物理学家都为之一震。但我们应该了解,这本书的目的是为了使控制仪表工程师充 分理解这一课题,从而可以安全的处理实用控制系统设计、运作、维护等方面的问题。1.2沸腾:水到蒸汽的状态变化 当水被加热时,其温度变化能通过某种途径被察觉(例如用温度计 。通过这种方式 得到的热量因为在某时水开始沸腾时其效果可被察觉,因而被称为感热。 然而,我们还需要更深的了解。“沸腾”究竟是什么含义?在深入了解之前,我们必须考虑到物质的三种状态:固态,液态,气态。 (当气体中的原子被电离时所产生的等离子气体经常被认为是物质的第四种状态, 但在实际应用中, 只需考虑以上三种状态固态,
物质由分子通过分子间的吸引力紧紧地靠在一起。当物质吸收热量,分子的能量升级并且 使得分子之间的间隙增大。当越来越多的能量被吸收,这种效果就会加剧,粒子之间相互脱离。这种由固态到液态的状态变化通常被称之为熔化。 当液体吸收了更多的热量时,一些分子获得了足够多的能量而从表面脱离,这个过程 被称为蒸发(凭此洒在地面的水会逐渐的消失在蒸发的过程中,一些分子是在相当低的 温度下脱离的,然而随着温度的上升,分子更加迅速的脱离,并且在某一温度上液体内部 变得非常剧烈,大量的气泡向液体表面升起。在这时我们称液体开始沸腾。这个过程是变为蒸汽的过程,也就是液体处于汽化状态。 让我们试想大量的水装在一个敞开的容器内。液体表面的空气对液体施加了一定的压 力,随着液体温度的上升,便会有足够的能量使得表面的分子挣脱出去,水这时开始改变 自身的状态,变成蒸汽。在此条件下获得更多的热量将不会引起温度上的明显变化。所增 加的能量只是被用来改变液体的状态。它的效用不能用温度计测量出来,但是它仍然发生 着。正因为如此,它被称为是潜在的,而不是可认知的热量。使这一现象发生的温度被称为是沸点。在常温常压下,水的沸点为100摄氏度。 如果液体表面的压力上升, 需要更多的能量才可以使得水变为蒸汽的状态。 换句话说, 必须使得温度更高才可以使它沸腾。总而言之,如果大气压力比正常值升高百分之十,水必须被加热到一百零二度才可以使之沸腾。