2022年文献翻译-数据采集和喷射噪音的控制系统参照

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1、数据采集和喷射噪音的控制系统自动化1 数据采集和喷射噪音的控制系统B.J.Jansen 美国航空暨太空总署Langley 研究中心的实验室航空宇宙流体声学学家美国航空暨太空总署Langley 研究中心摘 要美国航空暨太空总署兰利研究中心，喷射噪音实验室在展示了其数据采集的功能和控制系统性能，喷射噪音实验室是一个模拟现实的混合系统对火箭轮机式鼓风机喷射发动机喷嘴废气进行模拟。系统能够采集数据并为噪音和喷嘴运转进行评估。这篇论文阐述了改进的整合系统控制和测量喷管性能，并对喷嘴在双重的独立高压气流下工作噪音进行现实模拟。采集和控制系统能够同时测量瞬时力矩，静电和动态模型压力和温度以及喷射噪音。在设计

2、思想上讨论了控制计算机和多通路数据采集系统的结合。阐述了控制系统设计和实施，包括功能、设备和基于PC 机系统使用得经验等。关键字:数据采集，控制系统，喷射噪音,风洞1 绪 论研究喷射噪音的问题已有数年，自从各种喷射噪音产生在震动的机械装置包括液压管上,减少喷射噪音得课题便富有挑战性。喷射噪音的特殊部分，在美国航空暨太空总署火箭研究中心(LaRC)兰利喷射噪音实验室(JNL)中进行研究。噪音主要是喷射排气产生的。流体力学中，发生水柱噪音的现象是狂暴的混频,超音速的漩涡，电波幅射,通过陡震的狂暴漩涡，当宽频陡震噪音和共呜的陡震摆动共鸣时即出现噪音。为了有效对喷射噪声进行抑制，需要对其进行系统的研究

3、。首先要知道机械装置是怎么产生噪音的。对喷射噪声进行模拟仿真是最经济有效的方法。一个重要的特征是，现实喷射排气系统在高温燃烧的环境下产生喷射噪音，低温环境下的喷射噪音的减少并不代表在高温环境下就能抑制噪音。所以需要有一个研究系统能模拟现实的温度，压力和空气状况。2 数据采集系统什么是数据采集系统名师资料总结-精品资料欢迎下载-名师精心整理-第 1 页，共 13 页 -数据采集和喷射噪音的控制系统自动化2 数据采集系统，正如名字所暗示的，是一种用来采集信息成文件或分析一些现象的产品或过程。在最简单的形式中，技术人员将烤箱的温度记录在一张纸上就是数据采集。随着技术的发展，通过电子设备，这个过程已经

4、得到简化和变得比较精确、多用途和可靠。设备从简单的存储器发展到复杂的电脑系统。数据采集产品像聚焦点一样为系统服务，和一系列产品一起，诸如传感器显示温度、水流、程度或者过程。数据采集技术在过去30到 40年以来已经取得了很大的飞跃。举例来说,在 40 年以前,在一个著名的学院实验室中,为追踪用青铜做的坩埚中的温度上升情况的装置是由热电偶、继电器、查询台、一捆纸和一支铅笔。今天的大学学生很可能在PC 机上自动处理和分析数据，有很多种可供你选择的方法去采集数据。至于选择哪一种方法取决于多种因素，包括任务的复杂度、你所需要的速度和精度、你想要的证据资料等等。无论是简单的还是复杂的，数据采集系统都能够运

5、行并发挥它的作用。数字扫描多用表一些仪表提供可选择的扫描能力。仪器的背面有一个槽孔接收一张在较多输入时能多重发讯的扫描仪卡片，通常是8 到 10 通道的 mux。固有的在仪器的前面嵌板中的受到限制。它的柔韧性也受到限制，因为它不能超过可用通道数。外部的PC 机通常处理数据采集和分析。数据电子自动记录仪数据电子自动记录仪是典型的单机仪器，一旦配备它们,就能测量、记录和显示数据而不需要操作员或计算机参与。它们能够处理多信号输入，有时可达120 通道。精度可与无与伦比的台式DMMs 匹敌,由于它在 22 字、0.004个百分率的精度范围内运转。一些数据电子自动记录仪有能力按比例测量,检查结果不受使用

6、者定义的限制,而且输出为控制作信号。使用数据电子自动记录仪的一个好处就是他们的内部监测信号。大部分能够直接地测量若干不同的输入信号，而不需要额外的信号监测器件。一个通道能够监测热电偶、温阻器（RTD）和电压。热电偶为准确的温度测量提供具有参考价值的补偿，是很典型的配备了多路插件卡片。内设智能数据电子自动记录仪帮助你设定测量周期和具体指定每个通道的参数。一旦你全部设定好，数据电子自动记录仪就如同无与伦比的装置运行。它们存储的数据分布在内存中,能够容纳 500000或更多的阅读量。名师资料总结-精品资料欢迎下载-名师精心整理-第 2 页，共 13 页 -数据采集和喷射噪音的控制系统自动化3 前端数

7、据采集前端数据采集经常做成模块而且是典型地与PC 机或控制器连接。他们被用于自动化的测试中，为其它测试装备采集数据、控制和循环检测信号。发送信号测试装备的零配件。前端运转的效率是非常高的,能与速度和精度与最好的单机仪器匹敌。前端数据采集在很多模型里都能运行，包括 VXI 版本,如 Agilent E1419A 多功能测量和 VXI 控制模型，还有专有的卡片升降室。虽然前端器成本已经降低,但是这些系统可能会非常贵,除非你需要提供高的运转,而查找它们的价格是禁止的。另一方面,它们的确能够提供相当多的可挠性和测量能力。动态的数据采集系统动态的数据采集系统(DDAS)的读写频率可达到100 个千赫。J

8、NL（DDAS）以Sun 公司 SPARC10 VME 有 30个动态通道的总线计算机为基础。VME 阵列处理卡和数据采集系统连接起来进行数据分析（主要是快速的进行傅立叶变形)。JNL 有一个 28 传声器线性排别为记录浮凸槽喷射声。4136 1/4 型 Bruel&Kj 半径(B&K)设备和响应传声器和 2811 型混音器在工作中应用。传声器带宽扩充到大约100个千赫。利用喷嘴模型,动压力传感器安装到喷嘴表面进行内部表面压力测量。普通的感应器是Kulite 的XCE-093 半导体产品样板,3/32 直径和一个习惯设计水冷套箱用来保护感应器。B&K 2811 的直接输出buered,tere

9、d,和 ampli 由精密过滤器公司生产。这些通用接口总线的通带提供高频和低频对丘状焊痕达到102.3个千赫的转折频率进行选择。高频主要是4010 分贝的预先过滤。低频增益从0.1 个分贝的阶段9.9 到 30.0个分贝然后每个传声器的信号备分配到三个路径进入其中两个信号和A/D 转换器还有电压比较器进行数据类比数据在记录在TDR 存贮器中，用通用接口总线在GPIB IEEE-488 协议下，用 16位的并行总线和主机进行通信。并行总线的传送效率要达到170K/S，和 GPIB 的通信要达到 30KB/s,另外的一个数据集以一个较低的试样率被采集。通常由集成电路系统和16位 ICS-110VM

10、E 卡把频率限制在 62.5个千赫以下。通过32 通道的 VME 卡在 25 千赫的有限转折频率下，传声器信号存贮在ICS-110 卡上。如图 2.1A 所示是其动态数据系统的一个框图。DDAS 另外重要的部分是一个普通的 32 个通道的均方根(均方根)伏特计，并携带一个液晶显示(LCD)显示装置。均方根伏特计使用植入的Z80，它基于一个12 位 A/D 转换器用来测量直流电路输出的多重命令 Z80 计算机显示全部的传声器所排列的音量压力层次(SPL)，在 7x4 LCD 显示屏上，如图 2.1B 所示。DDAS 在 RMS 上读取电压信号，在TDR 数字化之前，选择传名师资料总结-精品资料欢

11、迎下载-名师精心整理-第 3 页，共 13 页 -数据采集和喷射噪音的控制系统自动化4 感器的增益信号 DDAS 不仅是系统主计算机,也是核心处理器。静电噪声数据采集系统(SDAS)设计成为记录缓慢多样信号的装置，并且计算在一定时间跨度上的信号平均值。JNL SDAS 是 Modcomp 结构计算机。Modcomp 是一个 6 U 的 VME 汇流系统，使用双重的摩托罗拉 88 K 处理器 REAL/IX real-time UNIX操作系统。（A）动态数据采集系统（B）RMS-DC SPL 计量器/显示装置如图 2.1:喷射噪音数据采集系统控制ICS-A/D 转换器在 VSB 总线上对 SU

12、N 磁盘写数据框图到美国航空暨太空总署的下属的Wyle 实验室对数据采集系统用在Modcomp 上的发展起到了很大的推动作用。它扮演了图解式，用户界面(图形用户接口)，即时图形显示装置,数据校正的持久性和采样频率等重要角色。各点的瞬间独立采样和平均值储存在磁盘上。3 系统的集成名师资料总结-精品资料欢迎下载-名师精心整理-第 4 页，共 13 页 -数据采集和喷射噪音的控制系统自动化5 整个 JNL DDAS 包含各种不同的仪器和处理器。主计算机本来是一个迪吉多电脑公司 Mcro-VAX 计算机，现在已经变成 Sun UNIX 操作系统。主机通过通用界面总线GPIB(通用接口总线)或 RS-2

13、32 连载通信。大部份原始数据采集软件被编码在FORTRON.迪吉多电脑公司从DEC 到 UNIX 操作系统转换主要通过RS-232通用接口总线和经过C语言编程的 GPIB 适配器。大部分工程师只对JNL 有 FORTRON 编程经验，而本系统 C语言功能建立起了对C 语言连载和通用接口总线功能的通道，几乎每个对JNL 编程都使用 C 语言、FORTROND 的结合。系统的最新仪器是VME 总线卡，操作系统和驱动器通过C 语言和系统建立通信。改良了数据采集功能的操作系统的特征，将其设置为可共享存储器。共享存储器允许复式的独立程序快速地彼此通信。在 UNIX 操作系统计算机上，C 语言功能建立了

14、共享存储器区域。区域的位址通过FORTRON 的子程序和它的命令来定义变量和内存的关系。这个共享功能可应用到迪吉多电脑公司的VMS 操作系统之下。连接计算机另外一个重要机械装置是网络。Wyle 中心发展的SDAS 包含了一个以柏克莱标准为基础的服务器程序分布(BSD)套筒。服务器能即时送出实时采集的平均数据,激活采取的一个数据点,即时接收数值，并且提供SDAS 状态信息。两个被改进的程序使DDAS 结合了这所有的功能。就象带 DSPM 测试服务的功能一样，一个称为 后台作业的即时程序提供了为监视设施和模型的虚拟化信息。后台作业共享存储器区域,设定与各种不同的仪器通信初值,通过 RS-232串行

15、接口和控制系统连接到 SDAS。然后进入一个读程序的的无限循环仪器SDAS，和控制系统评估,计算得数值如平均的压力和温度,最后送数值给SDAS 和控制系统。在设置之后，采集传感器信号的 DDAS 系统另一个主程序叫做lsawt这个程序是 SDAS 的数据采集程序，来调控(运转和模型气体力学的数据),控制系统和DDAS(电动微音器压力数据).一系列菜单给使用提供了最大的方便来变更缺省值，如传感器的数目记录,试样率,数据大小,和滤波频率。一旦操作员调整DSPM 使其达到必需的试验条件模式，数据采集系统和RMS-DC 通信便精确调整过滤器让它达到RMS 值。数据采集操作将DSPM 置于正确的条件下工

16、作而且数据可靠，主程序lsawt 程序将激活SDAS,(被设定 10 到 30 秒的平均值)8 秒 62.5 个千赫的 ICS-110 A 卡进行采样,Paci TDRs以 2 秒 250 个千赫采样。4 未来展望名师资料总结-精品资料欢迎下载-名师精心整理-第 5 页，共 13 页 -数据采集和喷射噪音的控制系统自动化6 需求带动着需求工具的发展。JNL 数据采集的方面和控制系统已经应用与其他领域。同时用一个高速输入输出设备代替Optomux 输入输出正在研究当做闭环控制改良系统的方法。安装一个在 TNT 软件下控制的 PC I/O 卡是一个不错得选择，加上一个可编程控制器或者其它品牌的控制

17、系统/软件包也正在被提上日程。Optomux 模拟输入是一个 12 位的 A/D 转换器和所需要的固定参数。当前12 位的数据译码和TDR S 的下载速度限制了 DDAS 系统。由于 12BIT 的译码范围，应设置使其达成最高的信噪比(SNR)和动力范围。未来的平台包括16位的 A/D 转换器，为采集信号提供一个动态的系统。脉冲准确话就可以很好的记录浮凸槽噪音数据。另外所有的通道含有时钟，对1V 的脉冲进行计数,在读取数值之前重新检测RMS值。喷射噪音的波峰因数靠近3(无正弦的)因此使用 RMS 不是一个可靠的方法。脉冲整定处理需要 2 到 5 分钟。限制 TDR 系统另外因素是下载速度过慢。

18、它要用4.5 分钟读出数据并在在DDAS硬盘上记录。在 DDAS 上读取记录大约需要两分钟。目前一个新型的经过了测试的产品面世了，它是基于AME 总线上的 16 位 A/D 卡和 250千赫的样率的A/D 转换器，它有一个高速的辅助数据接口，像当前所用的 SKYBolt 处理机一样。对于 32 个通道,数据总量的传送速率会达到八百万个试样/妙，或大约 15.26兆/妙。5 后记本文作者感谢火箭喷射噪音组（Aeroacoustic）对他论文的提供的支持和建议。另外很多人参与了本系统的构建。特别感谢美国航空暨太空总署工程师Seiner 麦可 Ponton，玛莎布朗.享利 Haskin,和罗勃特 G

19、randle,美国航空暨太空总署操作支持人员Cliord Williford，Gregory Hogge,贝芙丽钟斯Anderson，理查白.约翰 Swartzbaugh 和Fernandus Rattli,包括系统的承包商和普通工作人员查尔斯，锻造工卡尔戴维斯。参考文献1 Marquardt Company Burner Manual,1999 2 Rao.Guthikonda V.Microprocessors and micro computer system.V an Nostrand Reinhold company,1998 3 Maxin product selector Gui

20、de 2000 4 Huelsen,W.B.ASPECTS OF AUDIBLE NOISE CONTROL.Electric Furnace Conference Proceedings,Electr Furn Proc Metall Soc AIME,v 33,p 225-227,1985名师资料总结-精品资料欢迎下载-名师精心整理-第 6 页，共 13 页 -7 The Data Acquisition and Control Systems of the Jet Noise Laboratory at the NASA Langley Research Center B.J.Janse

21、n,Jr.Aerospace Technologist Fluid Mechanics And Acoustics Division NASA Langley Research Center ABSTRACT The features of the data acquisition and control systems of the NASA Langley Research Center s Jet Noise Laboratory are presented.The Jet Noise Laboratory is a facility that sim ulates realistic

22、mixed flow turbofan jet engine nozzle exhaust systems in simulated fight.The systems capable of acquiring data for a complete take-off assessment of noise and nozzle performance.This paper describes the development of an integrated system to control a n dm e a s u r et h eb e h a v i o ro fm o d e l

23、j e tn o z z l e s featuring dual independent high pressure combusting air streams with wind tunnel flow.The acquisition and control system is capable of simultaneous measurement of forces mom ents,static and dynamic m odel pressures and temperatures,and jet noise.The design concepts for the coordin

24、ation of the control computers and multiple data acquisition computers and instruments are discussed.The control systemdesign and implem entation are explained,describing the features,equipment,and the experiences of using a primarily Personal Computer based system.Areas for future development are e

25、xamined.KEYWORDS Data Acquisition,Control System,Jet Noise,Wind Tunnel 1 INTRODUCTION The problemof jet noise has been studied for many years.Since sound fromjets is generated by a variety of fluid mechanical mechanisms including tur bulence,reducing jet noise is challenging.The particular part of j

26、et 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 throug

27、h shocks denoted as broadband shock noise,and resonant shock oscillation known as screech.In order to make progress in the field of jet noise reduction,scientific research has been required to try to understand the physics behind the different noise generation mechanisms.The sim ulation of jet flows

28、 in model scale has been a cost effective way of achieving results.Animportantfeatureofrealjet 名师资料总结-精品资料欢迎下载-名师精心整理-第 7 页，共 13 页 -8 exhaust is the high temperatures of the combustion process and the affect of temperature on the noise generation mechanisms.Solutions that lead to the reduction of je

29、t noise sources in an unheated jet do not always leadto noise reduction in a hot jet.Reducing noise from jet aircraft requires a research facility that can simulate realistic temperatures,pressures.A norm al turbofan engine,typical of those in service on subsonic transports or jet fighters,have a ho

30、t combusting flow(core stream)surrounded by a cooler compressed flow(bypass or fan stream).2DATA ACQUISITION SYSTEMS What is DATA ACQUISITION SYSTEMS Data acquisition systems,as the name implies,are products and/or processes used to collect inform ation to docum ent or analyze som e phenom enon.In t

31、he sim plest form,a technician logging the temperature of an oven on a piece of paper is performing data acquisition.As technology has progressed,this type of process has been simplified and made more accurate,versatile,and reliable through electronic equipment.Equipment ranges from simple recorders

32、 to sophisticated computer systems.Data acquisition products serve as a focal point in a system,tying together a wide variety of products,such as sensors that indicatetem perature,flow,level,or pressure.Some common data acquisition terms are shown below.Data acquisition technology has taken giant le

33、aps forward over the last 30 to 40 years.For exam ple,40 years ago,in a typical college lab,apparatus for tracking the temperature rise in a crucible of sodium tungsten-bronze consisted of a thermocouple,a bridge,a lookup table,a pad of paper and a pencil.Today s college students are much m ore like

34、ly to use an automated process and analyze the data on a PC Today,numerous options are available for gathering data.The optimal choice depends on several factors,including the complexity of the task,the speed and accuracy you require,and the documentation you want.Data acquisition systems range from

35、 the sim ple to the complex,with a range of performance and functionality.Scanning digital multim eter Som e bench top DMMs offer an optional scanning capability.A slot in the rear of the instrument accepts a scanner card that can multiplex between multiple inputs,with 8 to 10 channels of mux being

36、fairly common.DMM accuracy and the functionality inherent in the instruments front panel are retained.Flexibility is limited in that it is not possible to expand beyond the number of channels available in the expansion slot.An external PC usually handles data acquisition and analysis.Data loggers Da

37、ta loggers are typically stand-alone instruments that,once they are setup,can measure,record and display data without operator or computer intervention.They can handle multiple inputs,in some instances up to 120 channels.Accuracy rivals that found in standalone bench DMMs,with performance in the 22-

38、bit,0.004-percent accuracy range.Som e data loggers have the ability to scale measurem ents,check results against user-defined limits,and output signals for control.One advantage of using data loggers is their built-in signal conditioning.Most are able to directly m easure a number of different inpu

39、ts without the need for additional signal 名师资料总结-精品资料欢迎下载-名师精心整理-第 8 页，共 13 页 -9 conditioning accessories.One channel could be monitoring a thermocouple,another a resistive temperature device(RTD)and still another could be looking at voltage.Therm ocouple reference com pensation for accurate tempera

40、ture measurem ent is typically built into the multiplexer cards.A data logger built-in intelligence helps you set up the test routine and specify the parameters of each channel.Once you have completed the setup,data loggers can run as standalone devices,much like a recorder.They store data locally i

41、n internal memory,which can accommodate 50,000 readings or more.Data acquisition front ends Data acquisition front ends are often modular and are typically connected to a PC or controller.They are used in automated test applications for gathering data and for controlling and routing signals in other

42、 parts of the test setup.Front end performance can be very high,with speed and accuracy rivaling the best standalone instruments.Data acquisition front ends are implemented in a number of formats,including VXI versions,such as the Agilent E1419A multifunction measurem ent and control VXI module,and

43、proprietary card cages.Although front-end cost has been decreasing,these systems can be fairly expensive,and unless you require the high performance they provide,you may find their price to be prohibitive.On the plus side,they do offer considerable flexibility and measurem ent capability.Dynam ic Da

44、ta Acquisition System The Dynam ic Data Acquisition System(DDAS)is designed to record tim e data with frequencies 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 perform ing data analysis

45、(primarily fast Fourier transforms)in conjunction with data acquisition.The JNL has a 28 microphone linear array for recording the far field jet acoustics.Br el&Kj?r(B&K)Instruments Type 4136 1/4 free field response microphones and Type 2811 Multiplexer Power Supplies are used.The microphone bandwid

46、th extends to about 100 KHz.Depending on the nozzle model,dynamic pressure sensors may be flush mounted to an internal part of the nozzle to measure the surface pressure fluctuations.The usual sensor is Kulite Semiconductor Products Model XCE-093,with a 3/32 diameter and a custom designed water cool

47、ing jacket is used to protect the sensor.The direct output of the B&K 2811 are buffered,filtered,and amplified by Precision Filters,Inc.System 6000 components.These GPIB programmable bandpass filter amplifiers provide low and high pass corner frequency selection up to 102.3 KHz,pre-filter gain of up

48、 to 40 dB in 10 dB steps,and post-filter gain from-9.9 to 30.0 dB by steps of 0.1 dB.Each microphone signal is then split into three paths:two different analog to digital(A/D)converter types and a custom 32 channel voltmeter.After data is recorded into the TDR mem ory,the host com puter downloads th

49、e information over a GPIB IEEE-488 bus interface or over the TDR 16 bit parallel bus through a custominterface 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 6

50、2.5 KHz with a 16 bit ICS-110A VME card from Integrated Circuits and System s Limited.The microphone signals recorded by the ICS-110A card are low-passed 名师资料总结-精品资料欢迎下载-名师精心整理-第 9 页，共 13 页 -10 through a 32 channel VME amplifier card with 25 KHz fixed corner frequency from Frequency Devices Incorpor

51、ated.A)Dynam ic Data Acquisition System B)RMS-DC SPL Meter/Display Figure 2:Jet Noise Dynamic Data Acquisition System Figure 2.1 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 2.1A shows a block diagram of the co

52、mplete 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 mul

53、tiplexed RMS to 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 2.1B).The DDAS reads the voltages on the RMS voltmeter to select amplifier gains of the m icrophone signals before digitizatio

54、n 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 com pute the average values of these signals over some time span.The JNL SDAS is a Modcomp Open Architecture com

55、puter.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 名师资料总结-精品资料欢迎下载-名师精心整理-第 10 页，共 13 页 -11 software used on the Modcomp was developed by Wyle Laboratories under contract to NASA.It features a graphical user int

56、erface(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.3 INTEGRATION OF SYSTEMS The entire JNL DDAS is comprised

57、 of a variety of different instruments and computers.The m ain computer originally was a DEC Micro-VAX computer but has been changed to a SUN UNIX system.Instrum entation connects to this host through the General Purpose Interface Bus(GPIB)or RS-232 serial communications.Most of the original data ac

58、quisition software was coded in FORTRAN.The main effect 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

59、 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

60、 and drivers.An operating system feature that improves the data acquisition programs is shared mem ory.Shared mem ory 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 pas

61、sed as an argument to a FORTRAN subroutine and the FORTRAN code uses a structure definition to define variables relative to mem ory locations.This sharing feature was also available under the DEC VMS operating system.Another important mechanism for connecting computers is by using the Ethernet netwo

62、rk.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 d

63、eveloped 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 commu

64、nication 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 val

65、ues 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

66、(dynamic m icrophone 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 filter cutoff frequencies.Once the operators have adjusted the 名师资料总结-精品资料欢迎下载-名师精心整理-第 11 页，共 13 页 -12 DSPM to the required test conditions,the data acquisition operator proceeds to the section of the program that communicates with the RMS-DC m eter and adjusts the Precision Filter gains to reach