冷库温度控制系统的设计 外文翻译

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 Acquisition

Date 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 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 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 and 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, 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 require 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. The 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 replaced 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 interest 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 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 transducers, 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 use 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 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 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. Microcomputer 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 sophistication, 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 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 ADC’s are faster than integrating ADC’s. 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 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 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 necessary 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 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 channel 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 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 controlled 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 instantaneous 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 units. 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 purposes 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 comparisons 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. ABSTRACT

The features of 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 complete 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 capable 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 are explained, describing the features, equipment, and the experiences of using a primarily Personal Computer based system. Areas for future development are examined.

2. INTRODUCTION

The problem of jet noise has been studied for many years. Since sound from jets is generated by a variety of uid mechanical 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 turbulent 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 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 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 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 SYSTEMS

The Dynamic Data Acquisition System (DDAS) is designed to record time data with frequence up to 100 KHz. The JNL 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 fareld jet acoustics. Br?uel & 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 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.

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 digital (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 transfer 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 32 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 system. 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 DC converter circuits. The Z80 computer displays the overall Sound Pressure Level (SPL) of the microphone array on a 7"x4" 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 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 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, user programmable equations and calibrations 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 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 cells 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 temperature 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 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 to 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 individual strain gauge pressure sensors (overall size of a module is about 2.5"x1.5"x1.5"). 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 process side of the sensors. The system includes working standard pressure sources

4. INTEGRATION OF SYSTEMS

The 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. 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 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 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 multiple independent programs to communicate with each other very rapidly.

On UNIX computers, the shared memory region is created by C functions. The address of the region is passed as an argument to a FORTRAN subroutine and the FORTRAN code uses a structure de_nition to de_ne variables relative to memory locations. This sharing feature was also available under the DEC VMS operating system.Another important mechanism for connecting computers is by using the Ethernet network. The SDAS developed by Wyle Labs included a server program that was based on Berkeley Standard Distribution (BSD) Sockets. The server can send out real time or averaged data, be triggered to take a data point, accept values into the system in real time, and provide SDAS status information.

Two programs developed for the DDAS combine all of these features and serve as the foundation for testing with the DSPM. A real time program called Background is designed to provide information for monitoring the conditions of the facility and model. Background establishes the shared memory region, initializes communication with various instruments, connects to the SDAS by sockets and the control system by RS-232. It then enters an endless loop in which it reads the instruments, SDAS, and control system values, calculates derived values such as average pressure and temperature at the charging station, then sends values to the SDAS and the control system. The other main program of the DDAS that acquires the microphone signals is named lsawt after the facility. This is the program that coordinates the data acquisition processes of the SDAS (for performance and model aerodynamic data), the

control system, and the DDAS (dynamic microphone and pressure data). A series of menus provide the user the opportunity to change default settings for such things as number of sensors to record, sample rate, size of the data set, and _lter cuto_ frequencies. Once the operators have adjusted the DSPM to the required test conditions, the data acquisition operator proceeds to the section of the program that communicates with the RMS-DC meter and adjusts the Precision Filter gains to reach the target RMS value. When the data acquisition operator is satis_ed that the DSPM is at the correct conditions and that the gains are acceptable, the lsawt program triggers the SDAS (which is set to average from 10 to 30 seconds) the ICS-110A card which samples at 62.5 KHz for 8 seconds, and the Paci_c TDRs which sample at 250 KHz for 2 seconds. The current values in the background program are written to a log _le at both the start and the end of the averaging period.

5. FUTURE IMPROVEMENTS

As research requirements change, so do the tools necessary to meet those requirements. Every aspect of the JNL data acquisition and control systems have been modi_ed in some way after entering service. The control system is currently inadequate for closed loop control of both burners simultaneously. Replacing some of the Optomux I/O with a higher speed type is being examined as a way of improving the system for closed loop control. Installing PC I/O cards that would still be controlled by the Paragon TNT software is one option. Adding a Programmable Logic Controller (PLC) or other brand of control system/software package that can be interfaced to Paragon TNT is being considered as well. The Optomux analog input is a 12 bit A/D converter and for certain parameters more resolution is desired. The DDAS is limited currently by the 12 bit resolution and the data download speed of the Paci_c Instruments TDRs. Because of the 12 bit resolution the gains must be set carefully to prevent clipping but achieve the highest signal to noise ratio (SNR) and dynamic range. Future plans include the purchase of 16 bit A/D converters, providing a _ner resolution which in turn gives a greater dynamic range for a given gain setting. The gains must be set just high enough to get above the _lter noise oor for good recording. meter for all channels, computing the gain required to get about 1 volt RMS, setting those gains, then rechecking the RMS values before taking data. Jet noise tends to have crest factors near 3(non-sinusoidal) and therefore using RMS is not a reliable way to prevent clipping. The gain setting process can take from 2 to 5 minutes.

The other limitation of the TDR system is the slow download speed. It takes approximately 4.5 minutes to read out the data and write it to disk on the DDAS computer.

The goal for setting the gains and having the data written out to the DDAS disks is a total of 2 minutes. One type of product that is being examined to meet this requirement is a VME bus based A/D card with 16 bit A/D converters that can sample at 250 KHz, with a high speed data port connected to an auxiliary processor (AP) like the SKYBolt currently used. For 32 channels, the aggregate data rate would be 8 million samples/second or about 15.26 MB/second.

6. ACKNOWLEDGMENTS

The author would like to thank the Jet Noise Group of the Aeroacoustic Branch for their support and comments during the development of the systems described in this paper. As with any project of this scope, many people were involved in building this entire system. In particular, I would like to recognize NASA engineers Jack Seiner, Michael Ponton, Martha Brown, Henry Haskin, and Robert Grandle, NASA operations support personnel Cli_ord Williford, Gregory Hogg, Beverly Jones Anderson, Richard White, John Swartzbaugh, and Fernandus Rattli_, and support contractors Jerry Lyle, Charles Smith, and Carl Davis.

数据采集

数据采集系统，用于采集运行中的数据，并存储在辅助存储器上，以供日后分析。许多数据采集系统以很高的速度获得这些数据，并且留给电脑很少的时间进行任何必要的或可取的数据操作或减少。所有数据都存储在辅助存储设备上，随后获得感兴趣的变量。设计专用的数据采集系统和接口来获得高速过程数据是非常必要的。这种特殊目的的设计可能是个昂贵的主张。

强大的迷你和主机计算机被用来将数据采集与其他功能,如比较实际输出和期望的输出值,然后决定控制行为,在预先设定的限制内采取措施保证产出变量。其计算能力需要将取决于类型的过程控制系统的实现。针对执行比例、比率或过程变量三项控制的软件需求相对琐碎,但微型计算机可用于实现这样的过程控制系统。它将不可能使用许多现有的微机的实施高速自适应控制系统必须使用合适的过程模型和可观的在线操作数据。

微机数据采集器是用来进行中间数据采集等功能于一体,在相对较低的速度,简单的数学操作的原始数据和一些形式的数据归算的。第一代数据采集器没有任何可编程计算机设备,采用慢速从一百个频道采集了数据。所有获得的数据可以在纸带上穿孔或打印之后的分析。这种硬件连线数据采集器被与微机结合、并可由用户编程的新一代数据采集器所取代。他们提供了一个极好的过程数据收集方法,采用标准化的接口,随后执行必要的操纵向过程操作员提供这有用的信息。获得的数据可用于分析在过程变量与开发自适应和优化过程控制必须的数学模型之间是否具有差异性。

数据采集器执行的数据采集功能在不同系统之间变化。简单的数据日志系统获得数据从几个通道而复杂系统接收数据从数百,甚至数千输入通道的分布在一个或多个过程。初步的数据采集器用扫描数来选择, 用一个顺序的方式连接到传感器或转换器,数据记录用数字格式。一个数据监测器在某个意义上说,它只能收集数据从特定类型的传感器及转换器。最好是使用非专用数据采集器因为任何传感器或转换器能被连接到使用适当的信号处理模块。微型计算机控制的数据采集便于大量的传感器扫描。扫描速率取决于信号动态，这意味着为了避免错误一些通道必须在非常高速扫描,而在较慢的速度扫描其他通道信息会有非常小的损失。在一些数据采集应用中，快速通道需要可达每秒100次的采样速度，而慢速通道可以每隔五分钟采样一次。传统的硬件接线、不可编程的数据采集器以一种连续的方式采样所有的通道，并且所有通道的采样频率都必须是相同。本程序的结果在积累了大量的数据,其中一些是不必要的,也减缓了全面有效的采样频率。和其它慢速通道相比，基于微机的数据采集器可用在较高频率下扫描快速通道。

绝大多数的用户可编程的数据采集器可以用来扫描1000个模拟和1000个数字输入通道。少量的数据采集器,具有较高的先进性,适合从15000模拟和数字通道获取数据。

数字通道的数据可以有以下几种形式:晶体管-晶体管逻辑或节点闭合信号。模拟数据必须被转换成数字形式记录并且必须使用合适的模拟/数字转换器(ADC)。ADC的特性能定义可实现的分辨率，以及不同通道都可以采样分析的速率。越来越多的用于提高位分辨率的A/D转换器。逐次逼近型ADC的分辨率比积分型ADC快。许多微型计算机控制的数据采集器一起使用包括设施规划通道扫描率。典型的扫描速率变化从每秒2频道到每秒10000个通道。

大多数数据采集器具有±0.01%或更好的分辨能力。也有可能达到1微伏的分辨率。从绝对意义上来说，分辨能力也取决于输入信号的范围,标准输入信号范围为0-10伏特、0-50伏特和0-100伏特。最低的可测量从1到50伏特的信号变化，使用在较小、可选范围内接收数据的模块可获得较高的采集精度。另一种是从数据采集器里得到的自动测距装置。

准确的数据获取、登陆合适的存储设备是十分重要的，因此对数据采集模块来说抑制共模噪声和共模电压是必要的。典型的共模噪声抑制能力在110dB-150dB范围之间，分贝(dB)即为定义为两种信号功率电平比值，因此,如果参考信号和实际信号的功率电平分别为Nr、Na,它们的比值为n分贝，其中

n = 10 Log10（Na/ Nr)

防止最大普通模式电压200至500伏特的典型可在微机数据采集器一起使用。

电压输入到一个单独的数据樵夫通道量测、规模化和线性化任何进一步的数据操作前或比较执行。

在许多情况下,有必要改变从某一特定输入传感器收到的数据信号所决定的特定通道的采样频率，因此，某种通道可能每隔10分钟采样一次，但是如果传感器信号逼近报警门限，很明显就需要每分钟、甚至更快的采样，这样就能使操作员能够及时获知信息,避免任何灾难的来临。微型计算机控制的智能数据采集器可编程用于改变基于过程信号值的采样频率，包含自扫描模块的其他数据采集器可以主动采样。

没有任何编程设施的传统硬件接线数据采集器,能简单地在固定采样间隔内记录传感元件输出的瞬时值，这个原始数据通常很少与典型用户相关。为了使其有意义,该数据必须使用校准曲线进行线化和调节,这样就能以适当的工程单位确定变量的真实值。在可编程数据采集器可用之前,该函数通常是在微型或大型计算机的离线模式上执行。原始数据值必须以二进制或八进制代码在纸带上打孔,用于输入计算机进行随后的分析目的,并转换为工程单位，纸带打孔是能降低通道扫描速度的低速机械装置，另一种是打印出原始数据值,并进一步降低数据扫描速率的装置，它不可能进行任何限制比较或提供任何报警信息。由数据采集器获取的每一个单值都必须进行记录,即使它可能在以后的分析中不起到任何有用的目的；另外许多数据值只需当他们处在预设低限和高限之外时进行记录。

1.摘要

美国国家航空和宇宙航行局兰利研究中心喷气机噪音实验室介绍了数据采集和控制系统的特点。喷气机噪声实验室模拟现实的混合设备, 建立拥有喷嘴喷气发动机排气系统。该系统能够获得一个完整的噪声和喷嘴性能评估数据。本文阐述了开发于一体的控制和测量喷气机喷嘴具有双重独立模型高压燃烧空气流与风隧道的综合性系统。

数据采集、控制系统能够同时测量力量、时刻、静态和动态控制模型的压力和温度,和喷气机的噪声。为协调控制计算机和多种数据采集计算机和仪器的设计概念进行了讨论。对控制系统的设计与实现进行解释,指出描述的特点,设备和经验的个人电脑使用主要基于系统。检查未来的发展领域。

2.引言

喷气机噪声的问题已经被研究了许多年。自从喷气机噪声产生于多种机械机制包括湍流,减少喷气机噪声是有挑战性的。美国国家航空和宇宙航行局兰利研究中心(LaRC) 喷气机噪声实验室(JNL)研究喷气机噪声是由喷射排气噪声,或羽毛产生。流体力学现象产生的羽流噪声是紊流混合、超音速艾迪马赫波辐射、噪声产生的旋涡通过湍流冲击噪声宽带冲击作为属性,共振冲击振动称为尖叫。为了取得新进展的喷气机降噪，研究需要试着去了解背后的物理噪声产生的机理。仿真模型在射流规模上取得了巨大的成果。真正喷气机的一个重要特征是高温尾气燃烧过程和行为温度对噪声产生的机理。在一个不能供热的环境下导致喷气机的噪音减少,并不总是喷气机降噪热的解决方案。喷气机噪音大大降低,需要从一个研究机构,可以制作出逼真的温度、压力。一个正常的涡扇发动机，一般用于亚音速运输喷气机，有一个热燃烧机制（核心流）包围一个冷却的压缩机制（旁路或风扇流）。

3.数字采集系统

动态数据采集系统(DDAS)是用来记录时间数据,高达100千赫兹的频率。JNL DDAS 是基于SUN SPARC10 VME计算记录能力为30个动态通道。一个VME阵列处理卡是包括了执行数据分析(主要是快速傅里叶变换)和结合数据采集。JNL拥有28个传音器线性数组记录喷气机噪音的情况。Br_uel和Kj_r (B&K)仪器4136 1/4型自由响应传音器和2811型多路复用器电源使用。传音器带宽延伸到大约100千赫兹。根据喷嘴模型、动态压力传感器安装可以推一个内部的部分测量表面压力喷嘴。通常的传感器产品模型XCE- 093, 直径3/32英寸，常规设计水冷夹是用来保护传感器。精密过滤器B&K2811的直接输出是改变的。

通过这些GPIB可编程的器件提供低通和高通过拐角频率选择102.3 KHz,压力以10分贝为阶梯增加到40分贝为止,以0.1分贝为阶梯从-9.9分贝增加到30.0分贝。每一个话筒信号分成了三个部分:两个模拟到数字(A/D) 类型转换器和一个定制的32路的电压表。数据记录到TDR存储器,主机通过一个定制的主计算机在GPIB IEEE - 488总线接口或者在TDR 16位并行总线接口电路中下载信息。并行总线传输速率约为170 KB /秒GPIB接口速率约30 KB/秒。从集成电路与系统有限公司的16位62.5千赫兹ICS-110A VME卡上，以低采样率获得另一个数据集。

从频率设备股份有限公司通过32路拐角频率25 KHz 的VME卡记录传音器信号。

图3.1是动态数据采集系统噪声控制ICS A/D卡通过VSB写数据到SUN硬盘。

图3 A显示了一个完整的动态数据系统框图。另一个重要的组成部分,是一个定制的DDAS均方根(RMS)32频道电压表和液晶显示屏(LCD)显示。电压表使用的均方根值基于嵌入式Z80单板机控制,通过Z-World 12位A/D转换器测量输出有效值电路,多路直流转换器。电脑显示器整体的Z80声压级(SPL)的传音器阵列在7×4英寸液晶屏幕上显示一个条形图的格式(图3 B)。DDAS读取电压值是在TDR信号数字化前对RMS电压表进行选择所得。DDAS电脑的中央控制器，并不是唯一的电脑系统。静态数据采集系统(SDAS)用来记录不同的信号和计算这些信号时间跨度缓慢的平均值。JNL SDAS是一个开放体系结构的计算机。这是一个6-U VME总线系统使用在双摩托罗拉88 K的CPU和REAL/IX 实时UNIX操作系统上。数据采集软件应用于美国国家航空和宇宙航行局诺拉怀尔实验室。它的特性包括一个图形用户接口(GUI)、实时图形显示，用户可编程的方程和校准渠道，可调数据点时间和采样率。个人样品对点时间平均值可以保存到磁盘。

模拟输入系统是一个仪器公司620系列600型号，其中有一个100千赫采样率16位A/D转换器,可以扫描每512个通道系统。JNL Ne_ 620的一个机架安装单元有64个频道。Ne_ 620还提供高通和低通。负载平衡力通过单元提供动力的Ne_620系列300信号调节器。负荷单元全桥内置温度补偿。热偶是连接到Ne_600通过仪器温度均匀性很好的参考板(UTR)。该零件终端带钢一个100欧姆的铂电阻温度检测器(RTD)测量冷端温度补偿导线板改变铜绞线电线。用软件编程来校正冷端温度，并进行了多项式电压推导出热电偶温度。SDAS另一个主要部分的性能是衡量静态压力。设置飞机关键操作条件的总压力,而上游喷管(称为充电站)喷嘴也有测压孔模型沿墙内部速度可以使计算进行比较的解决方案。其他压力探针测量使用远程定位在实际射流排气烟羽。JNL运用电子扫描压力(ESP)系统和压力系统(PSI)。本产品由传感器模块16,32,48或64个人应变压力传感器模块(总体规模大小约2.5X1.5X1.5)。在一个16位A/D转换器以50千赫兹采样前多路传感器与每个模块和其他外部连接。每个模块已建成了校准压力阀,可以用于工艺一侧的传感器。该系统包括工作标准压力来源。

4.集成系统

JNL DDAS是由许多仪表和计算机组成的。主机是DEC Micro-VAX，但已经换成了一个SUN UNIX系统。仪表连接到该主机通过通用接口总线(GPIB)或RS—232串行通信。大多数的原始数据采集软件编码FORTRAN语言。主要方法从DEC切换到UNIX是软件来访问RS - 232串口和通用接口总线适配器，现在是通过C语言。大部分的JNL工程师们只有FORTRAN编程经验,所以一组C函数是用来简化访问C系列、GPIB和FORTRAN语言特征的通用接口总线。几乎JNL每一个项目的都是C和FORTRAN程序的联合作用。最新仪器VME总线系统的卡片,它能够通过C语言基础操作系统功能和运行。

共享内存提高了一个操作系统的数据采集功能。共享内存允许多个独立程序快速的来进行彼此的沟通。在UNIX计算机,共享内存区是由C功能建立。区域的地址被作为一个参数传递到一个FORTRAN程序代码和FORTRAN语言同样结构的变量的内存位置。这种共享的特征是也可用在DEC VMS操作系统。另一个重要的机制,是连接计算机利用以太网网络。诺拉·怀尔实验室开发的性能包括一个服务器程序,它是基于美国加州大学柏克莱分校的标准分布(BSD)接口。服务器可以送出真正的时间和平均数据,被触发而采取一个数据点,接受系统实时处理的数据值,并提供性能状态信息。

DDAS的两个项目结合了所有的这些功能和服务的基础与DSPM测试。提出了一种实时节目背景的目的是提供信息,用于监视设备和条件模型。背景建立共享内存区域,通信和各类仪器设备初始化,通过插座连接性能并由RS-232控制系统。然后进入一个死循环中,它读取仪器、性能、以及控制系统的数值,导出平均压力和温度计算值,然后送给SDAS 同时控制系统的性能。DDAS其他主要项目获得传音器信号后被命名。这是程序,配合SDAS(为了性能和模型气动数据)数据采集过程性能的分析,以及DDAS(麦克风和压力资料)控制系统。

一系列的菜单提供用户机会改变默认设置，例如传感器记录的数量、采样率、数据集的大小,以及频率。一旦运营商DSPM调整到所需的试验条件、数据采集经营者提供了部分的程序,用相同的RMS-DC仪表和调整精密过滤器的收益均方根值来实现这个目标。当DSPM采集数据，是在正确的条件和可以接受的增益下，程序触发的的SDAS（设置平均从10到30秒）ICS-110A卡用8秒采样62.5千赫兹，Paci_c TDRs卡2秒采样250千赫兹。当前值在后台写一个开始和结束时的平均周期的日志。

5.未来的改进

为研究需求的变化,所以做必要的工具来满足这些需求。JNL的每一个方面让数据采集和控制系统已经在某种程度上进入服务。该控制系统是目前不适用于闭环控制的两个燃烧器同时进行。更换部分的I/O和更高的速度打字是提高整个系统的闭环控制的一种方式。安装计算机I/O卡是一个可以控制TNT软件的选择。添加一个可编程逻辑控制器(PLC)控制系统或其他控制系统/软件包,可以用于TNT作为模板。这是一个理想的模拟

输入12位A/D转换器和较多特定参数的设计。目前的DDAS是有限的12位分辨率和有限的数据下载速度。因为得到了12位分辨率必须设置防止削波,但会取得最高的信噪比(SNR)和动态范围。未来的计划包括购买16位A/D转换器,为设置一个给定的增益更大的动态范围提供一个解决方案。增益就必须设置足够高,使获得较好的噪声记录。为所有频道计算增益要求做到大约1伏特，设置增益,然后在获得数据前不断地复查有效值的数据。喷气机噪声产生3个因素（非正弦），因此使用RMS不是一个防止削波的可靠方法。增益设置过程需要2到5分钟。

TDR系统的另一个限制是缓慢的下载速度。需要大约4.5分钟来读数据,并把它记录到DDAS电脑的磁盘上。目标增益的设定和写数据到DDAS的磁盘一共用2分钟。现正研究一个类型的产品，以满足这一要求是基于VME总线的16位的A/D转换器，可在250 kHz 采样的A/D卡，连接到一个辅助处理器（AP），如目前使用的高速数据端口。32通道的,总的数据比例每秒达800万个样本或每秒15.26MB。

6.致谢

感谢射流噪声集团的Aeroacoustic分公司,感谢他们的支持和系统开发过程中的意见。在此范围内的任何项目,许多人积极参与到整个系统的建立。我特别想要认识到美国宇航局的工程师们杰克,迈克尔·波顿,玛莎·布朗,亨利·哈斯和罗伯特·格兰德,美国宇航局专业支持人员,格雷戈里·霍格,贝弗莉·琼斯·安德森,理查德白色,约翰·施瓦尔兹,费尔南德斯·瑞塔里,支持承包商杰瑞·莱尔,查尔斯·史密斯,和卡尔·戴维斯。