冷庫(kù)溫度控制系統(tǒng)的設(shè)計(jì)-外文翻譯

1、大連交通大學(xué)信息工程學(xué)院畢業(yè)設(shè)計(jì)(論文)外文翻譯學(xué)生姓名 1111 專業(yè)班級(jí) 自動(dòng)化0111班 指導(dǎo)教師 1111 職 稱 11111 所在單位 電氣工程系 教研室主任 完成日期 1111 年 4 月 13 日Date AcquisitionDate acquisition systems are used to acquire process operating data and store it on secondary storage devices for later analysis. Many of the data acquisition systems acquire this

2、 data at very high speeds and very little computer time is left to carry out any necessary, or desirable, data manipulations or reduction. All the data are stored on secondary storage devices and manipulated subsequently to derive the variables of interest. It is very often necessary to design speci

3、al purpose data acquisition systems and interfaces to acquire the high speed process data. This special purpose design can be an expensive proposition.Powerful mini- and mainframe computers are used to combine the data acquisition with other functions such as comparisons between the actual output an

4、d the desirable output values, and to then decide on the control action which must be taken to ensure that the output variables lie within pre-set limits. The computing power required will depend upon the type of process control system implemented .Software requirements for carrying out proportional

5、, ratio or three term control of process variables are relatively trivial , and microcomputers can be used to implement such process control systems . It would not be possible to use many of the currently available microcomputers for the implementation of high speed adaptive control systems which re

6、quire the use of suitable process models and considerable on-line manipulation of data.Microcomputer based data loggers are used to carry out intermediate functions such as data acquisition at comparatively low speeds, simple mathematical manipulations of raw data and some forms of data reduction. T

7、he first generation of data loggers, without any programmable computing facilities, were used simply for slow speed data acquisition from up to one hundred channels. All the acquired data could be punched out on paper tape or printed for subsequent analysis. Such hardwired data loggers are being rep

8、laced by the new generation of data loggers which incorporate microcomputers and can be programmed by the user. They offer an extremely good method of collecting the process data, using standardized interfaces, and subsequently performing the necessary manipulations to provide the information of int

9、erest to the process operator. The data acquired can be analyzed to establish correlations, if any, between process variables and to develop mathematical models necessary for adaptive and optimal process control.The data acquisition function carried out by data loggers varies from one logging system

10、 to another. Simple data logging systems acquire data from a few channels while complex systems can receive data from hundreds, or even thousands, of input channels distributed around one or more processes. The rudimentary data loggers scan select number of channels, connected to sensors or transduc

11、ers, in a sequential manner and the data are recorded in digital format. A data logger can be dedicated in the sense that it can only collect data from particular types of sensors and transducers. It is best to use a non-dedicated data logger since any transducer or sensor can be connected to the us

12、e of appropriate signal conditioning modules.Microcomputer controlled data acquisition facilitates the scanning of a large number of sensors. The scanning rate depends upon the signal dynamics which means that some channels must be scanned at very high speeds in order to avoid aliasing errors while

13、here is very little loss of information by scanning other cannels at slower speeds. In some data logging applications the faster channels require sampling at speeds of up to 100 times per second while slow channels can be sampled once every five minutes. The conventional hardwired, non-programmable

14、data loggers sample all the channels in a sequential manner and the sampling frequency of all the channels must be the same. This procedure results in the accumulation of very large amounts of data, some of which is unnecessary, and also slows down the overall effective sampling frequency. Microcomp

15、uter based data loggers can be used to scan some fast channels at a higher frequency than other slow speed channels.The vast majority of the user programmable data loggers can be used to scan up to 1000 analog and 1000 digital input channels. A small number of data loggers, with a higher degree of s

16、ophistication, are suitable for acquiring data from up to 15,000 analog and digital channels. The data from digital channels can be in the form of Transistor-Transistor Logic or contact closure signals. Analog data must be converted into digital format before it is recorded and requires the use of s

17、uitable analog to digital converters (ADC). The characteristics of the ADC will define the resolution that can be achieved and the rate at which the various channels can be sampled. An increase in the number of bits used in the ADC improves the resolution capability. Successive approximation ADCs ar

18、e faster than integrating ADCs. Many microcomputer controlled data loggers include a facility to program the channel scanning rates. Typical scanning rates vary from 2channels per second to 10,000 channels per second.Most data loggers have a resolution capability of 0.001% or better. It is also poss

19、ible to achieve a resolution of 1 micro-volt. The resolution capability, in absolute terms, also depends upon the range of input signals, Standard input signal ranges are 0-1- volt, 0-50 volt and 0-100 volt. The lowest measurable signal varies form 1 u volt to 50 u volt .A higher degree of recording

20、 accuracy can be achieved by using modules which accept data in small, selectable rages. An alternative is the auto ranging facility available on some data loggers.The accuracy with which the data are acquired and logged on the appropriate storage device is extremely important. It is therefore neces

21、sary that the data acquisition module should be able to reject common mode noise and common mode voltage. Typical common mode noise rejection capabilities lie in the range 110 dB to 150dB. A decibel (dB) is a term which defines the ratio of the power levels of two signals. Thus if the reference and

22、actual signals have power levels of Nr and Na respectively, they will have a ratio of n decibels, where n=10 Log 10 (Na /Nr) Protection against maximum common mode voltages of 200 to 500 volt is available on typical microcomputer based data loggers.The voltage input to an individual data logger chan

23、nel is measured, scaled and linearised before any further data manipulations or comparisons are carried out.In many situations, it becomes necessary to alter the frequency at which particular channels are sampled depending upon the values of data signals received from a particular input sensor. Thus

24、 a channel might normal be sampled once every 10 minutes. If, however, the sensor signals approach the alarm limit, then it is obviously desirable to sample that channel once every minute or even faster so that the operators can be informed, thereby avoiding any catastrophes. Microcomputer controlle

25、d intelligent data loggers may be programmed to alter the sampling frequencies depending upon the values of process signals. Other data loggers include self-scanning modules which can initiate sampling.The conventional hardwired data loggers, without any programming facilities, simply record the ins

26、tantaneous values of transducer outputs at a regular sampling interval. This raw data often means very little to the typical user. To be meaningful, this data must be linearised and scaled, using a calibration curve, in order to determine the real value of the variable in appropriate engineering uni

27、ts. Prior to the availability of programmable data loggers, this function was usually carried out in the off-line mode on a mini- or mainframe computer. The raw data values had to be punched out on paper tape, in binary or octal code, to be input subsequently to the computer used for analysis purpos

28、es and converted to the engineering units. Paper tape punches are slow speed mechanical devices which reduce the speed at which channels can be scanned. An alternative was to print out the raw data values which further reduced the data scanning rate. It was not possible to carry out any limit compar

29、isons or provide any alarm information. Every single value acquired by the data logger had to be recorded even though it might nit serve any useful purpose during subsequent analysis; many data values only need recording when they lie outside the pre-set low and high limits.1. ABSTRACTThe features o

30、f the data acquisition and control systems of the NASA Langley Research Centers Jet Noise Laboratory are presented. The Jet Noise Laboratory is a facility that simulates realistic mixed ow turbofan jet engine nozzle exhaust systems in simulated ight. The systems capable of acquiring data for a compl

31、ete take-o_ assessment of noise and nozzle performance.This paper describes the development of an integrated system to control and measure the behaviorof model jet nozzles featuring dual independent high pressure combusting air streams with wind tunnel ow. The acquisition and control system is capab

32、le of simultaneous measurement of forces,moments, static and dynamic model pressures and temperatures, and jet noise. The design conceptsfor the coordination of the control computers and multiple data acquisition computers and instruments are discussed. The control system design and implementation a

33、re explained, describing the features, equipment, and the experiences of using a primarily Personal Computer based system. Areas for future development are examined.2. INTRODUCTIONThe problem of jet noise has been studied for many years. Since sound from jets is generated by a variety of uid mechani

34、cal mechanisms including turbulence, reducing jet noise is challenging. The particular part of jet noise studied in the Jet Noise Laboratory (JNL) of the NASA Langley Research Center (LaRC) is the noise generated by the jet exhaust, or plume. Fluid mechanic phenomenon that generate plume noise are t

35、urbulent mixing, supersonic eddy Mach wave radiation,noise generated by turbulent eddies passing through shocks denoted as broadband shock noise, and resonant shock oscillation known as screech. In order to make progress in the _eld of jet noise reduction, scienti_c research has been required to try

36、 to understand the physics behind the dierent noise generation mechanisms. The simulation of jet ows in model scale has been a cost eective way of achieving results. An important feature of real jet exhausts is the high temperatures of the combustion process and the aect of temperature on the noise

37、generation mechanisms. Solutions that lead to the reduction of jet noise sources in an unheated jet do not always lead to noise reduction in a hot jet. Reducing noise from jet aircraft requires a research facility that can simulate realistic temperatures, pressures. A normal turbofan engine, typical

38、 of those in service on subsonic transports or jet _ghters, have a hot combusting ow (core stream) surrounded by a cooler compressed ow (bypass or fan stream). 3. DATA ACQUISITION SYSTEMSThe Dynamic Data Acquisition System (DDAS) is designed to record time data with frequence up to 100 KHz. The JNL

39、DDAS is based on a SUN SPARC10 VME bus computer with recording capacity of 30 dynamic channels. A VME array processing card is included for performing data analysis (primarily fast Fourier transforms) in conjunction with data acquisition. The JNL has a 28 microphone linear array for recording the fa

40、reld jet acoustics. Bruel & Kj_r (B&K) Instruments Type 4136 1/4 free _eld response microphones and Type 2811 Multiplexer Power Supplies are used. The microphone bandwidth extends to about 100 KHz. Depending on the nozzle model,dynamic pressure sensors may be ush mounted to an internal part of the n

41、ozzle to measure the surface pressure uctuations. The usual sensor is Kulite Semiconductor Products Model XCE-093,with a 3/32 diameter and a custom designed water cooling jacket is used to protect the sensor. The direct output of the B&K 2811 are buered, ltered, and amplied by Precision Filters, Inc

42、.These GPIB programmable bandpass ampliers provide low and high pass corner frequency selection up to 102.3 KHz, pre-_lter gain of up to 40 dB in 10 dB steps,and post-_lter gain from -9.9 to 30.0 dB by steps of 0.1 dB. Each microphone signal is then split into three paths: two dirent analog to digit

43、al (A/D) converter types and a custom 32 channel voltmeter.After data is recorded into the TDR memory, the host computer downloads the information over a GPIB IEEE-488 bus interface or over the TDR 16 bit parallel bus through a custom interface circuit into the host computer. The parallel bus transf

44、er rate is about 170 KB/sec versus about 30 KB/sec for the GPIB interface. Another data set is acquired at a lower sample rate,usually 62.5 KHz with a 16 bit ICS-110A VME card from Integrated Circuits and Systems Limited.The microphone signals recorded by the ICS-110A card are low-passed through a 3

45、2 channel VME ampli_er card with 25 KHz _xed corner frequency from Frequency Devices Incorporated.Figure 3.1 Noise Dynamic Data Acquisition System card) controls the ICS A/D card over the VSB bus the writes the data to the SUN hard disks.Figure 3A shows a block diagram of the complete dynamic data s

46、ystem. Another important part of the DDAS is a custom 32 channel Root-Mean-Square (RMS) voltmeter with a Liquid Crystal Display (LCD) display. The RMS voltmeter uses an embedded Z80 based single board computer by Z-World that has a 12 bit A/D converter to measure the output of the multiplexed RMS to

47、 DC converter circuits. The Z80 computer displays the overall Sound Pressure Level (SPL) of the microphone array on a 7x4 LCD screen in a bar graph format (Figure 3B). The DDAS reads the voltages on the RMS voltmeter to select ampli_er gains of the microphone signals before digitization by the TDR.

48、The DDAS computer, while the central controller, is not the only computer in the system. The Static Data Acquisition System (SDAS) is designed to record slowly varying signals and compute the average values of these signals over some time span. The JNL SDAS is a Modcomp Open Architecture computer. T

49、he Modcomp is a 6-U VME bus system using dual Motorola 88K CPUs and the REAL/IX real-time UNIX operating system. The data acquisition software used on the Modcomp was developed by Wyle Laboratories under contract to NASA. It features a graphical user interface (GUI), real time graphics displays, use

50、r programmable equations and calibrations forchannels, and adjustable data point duration and sampling rate. Both individual samples and the average values over the point duration can be saved to disk.The analog input system is a Ne_ Instrument Corporation System 620 Series 600 which has a 100 KHz s

51、ample rate 16 bit A/D converter and can scan up to 512 channels per system. The JNL Ne_ has 64 channels in one 7 rack mount unit. The Ne_ 620 also supplies ampli_cation and low pass _lters. The force balance load cells are powered through a Ne_ System 620 Series 300 signal conditioner. The load cell

52、s are full bridge with built-in temperature compensation. Thermocouples are connected to the Ne_ Series 600 through a Kaye Instruments Uniform Temperature Reference plate (UTR). This isothermal terminal strip has a 100 Ohm platinum resistance temperature detector (RTD) to measure the cold junction t

53、emperature of the plate where the speci_c thermocouple wire changes to twisted pair copper wiring. The Modcomp software is programmed to correct for the cold junction temperature and performs a multi-zone polynomial _t of the thermocouple voltage to derive temperature. Another major part of the SDAS

54、 is the measurement of static pressures. Critical to setting the jet operating conditions are the total pressures just upstream of the nozzle exit (termed the charging station) The nozzle models might also have pressure taps along the wall so that internal velocity can be calculated for comparison t

55、o computational uid mechanics solutions. Other pressures are measured using probes remotely positioned in the actual jet exhaust plume. The JNL uses the Electronically Scanned Pressure (ESP) System from Pressure Systems Incorporated (PSI). This product consists of sensor modules of 16, 32, 48, or 64

56、 individual strain gauge pressure sensors (overall size of a module is about 2.5x1.5x1.5). The sensors are multiplexed in each module and at other external junctions before being measured by a 16 bit A/D converter capable of sampling at 50 KHz. Each module has a built in valve so that calibration pr

57、essures may be applied to the process side of the sensors. The system includes working standard pressure sources 4. INTEGRATION OF SYSTEMSThe entire JNL DDAS is comprised of a variety of di_erent instruments and computers. The main computer originally was a DEC Micro-VAX computer but has been change

58、d to a SUN UNIX system. Instrumentation connects to this host through the General Purpose Interface Bus (GPIB) or RS-232 serial communications. Most of the original data acquisition software was coded in FORTRAN. The main e_ect of switching from DEC to UNIX was that the software for accessing RS-232

59、 serial ports and GPIB adapter were now through the C language. Most of the engineers supporting the JNL had only FORTRAN programming experience, so a set of C functions were created to simplify access to the C serial and GPIB features from the FORTRAN language. Almost every program for the JNL uses

60、 a combination of C and FORTRAN routines. The newest instrument additions to the system are VME bus cards which are accessed through C language based operating system functions and drivers.An operating system feature that improves the data acquisition programs is shared memory. Shared memory allows