冷库温度控制系统的设计 外文翻译

1、大连交通大学信息工程学院毕业设计(论文外文翻译学生姓名 1111 专业班级自动化0111班指导教师 1111 职称 11111所在单位电气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 data at

2、 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 special purpo

3、se 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 and the de

4、sirable 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, ratio

5、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 require th

6、e 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. The first

7、 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 replaced by

8、 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 interest to

9、 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 to anot

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

11、 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 use of appr

12、opriate 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 here is v

13、ery 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 data logg

14、ers 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. Microcomputer base

15、d 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 sophistica

16、tion, 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 suitable a

17、nalog 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 are faster t

18、han 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 possible to ac

19、hieve 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 accuracy

20、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 necessary that

21、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 actual sign

22、als have power levels of Nr and Na respectively, they will have a ratio of n decibels, wheren=10 Log 10 (Na /NrProtection 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 channel is measure

23、d, 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 a channel mig

24、ht 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 controlled intelligent

25、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 instantaneous val

26、ues 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 units. Prior to t

27、he 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 purposes and convert

28、ed 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 comparisons or provi

29、de 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 of the data acq

30、uisition 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 complete take-o_ as

31、sessment 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 capable of simultan

32、eous 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 are explained,

33、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 mechanical mechanisms

34、 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 turbulent mixing,

35、 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 to understand t

36、he 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 generation mecha

37、nisms. 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 of those in ser

38、vice 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 DDAS is based on a S

39、UN 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 fareld jet acoustics. B

40、ruel & 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 nozzle to measure the s

41、urface 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.These GPIB programmab

42、le 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 digital (A/D converter type

43、s 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 transfer rate is about 170 KB

44、/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 32 channel VME ampli_er

45、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 system. Another important

46、 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 DC converter circuits. Th

47、e 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. The DDAS computer, while the

48、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. The Modcomp is a 6-U VME bus sy

49、stem 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, user programmable equations and ca

50、librations for channels, 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 sample rate 16 bit A/D converte

51、r 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 cells are full bridge with built-i

52、n 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 temperature of the plate where th

53、e 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 is the measurement of static pr

54、essures. 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 to computational uid mechanics sol

55、utions. 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 individual strain gauge pressure s

56、ensors (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 pressures may be applied to the proces

57、s side of the sensors. The system includes working standard pressure sources4. 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 changed to a SUN UNIX system. Instrumentati

58、on 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 serial ports and GPIB adapter were no

59、w 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 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 progr