【文章內(nèi)容簡介】 er 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 amp。 Kj_r (Bamp。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 XCE093,with a 3/32 diameter and a custom designed water cooling jacket is used to protect the sensor. The direct output of the Bamp。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 KHz, pre_lter gain of up to 40 dB in 10 dB steps,and post_lter gain from to dB by steps of dB. Each microphone signal is then split into three paths: two dirent analog to digital (A/D) converter types and a custom 32 channel data is recorded into the TDR memory, the host puter downloads the information over a GPIB IEEE488 bus interface or over the TDR 16 bit parallel bus through a custom interface circuit into the host puter. 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 KHz with a 16 bit ICS110A VME card from Integrated Circuits and Systems Limited. The microphone signals recorded by the ICS110A card are lowpassed through a 32 channel VME ampli_er card with 25 KHz _xed corner frequency from Frequency Devices Incorporated. Figure 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 plete dynamic data system. Another important part of the DDAS is a custom 32 channel RootMeanSquare (RMS) voltmeter with a Liquid Crystal Display (LCD) display. The RMS voltmeter uses an embedded Z80 based single board puter by ZWorld that has a 12 bit A/D converter to measure the output of the multiplexed RMS to DC converter circuits. The Z80 puter displays the overall Sound Pressure Level (SPL) of the microphone array on a 7x4 LCD screen in a bar graph format 大連 交通大學信息工程 學院 2021 屆本科生畢業(yè)設計（論文）外文翻譯 6 (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 puter, while the central controller, is not the only puter in the system. The Static Data Acquisition System (SDAS) is designed to record slowly varying signals and pute the average values of these signals over some time span. The JNL SDAS is a Modp Open Architecture puter. The Modp is a 6U VME bus system using dual Motorola 88K CPUs and the REAL/IX realtime UNIX operating system. The data acquisition software used on the Modp 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 builtin temperature pensation. 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 Modp software is programmed to correct for the cold junction temperature and performs a multizone 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 parison to putational 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 ). 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 大連 交通大學信息工程 學院 2021 屆本科生畢業(yè)設計（論文）外文翻譯 7 4. INTEGRATION OF SYSTEMS The entire JNL DDAS is prised of a variety of di_erent instruments and puters. The main puter originally was a DEC MicroVAX puter but has been changed to a SUN UNIX system. Instrumentation connects to this host through the General Purpose Interface Bus (GPIB) or RS232 serial munications. Most of the original data acquisition software was coded in FORTRA