Real-time Data Acquisition System Research Articles

Distributed Sensing and Control Technology for Intelligent Civil Infrastructure Systems

Abstract: Sensing and control functions are the fundamental technologies on which many civil infrastructure control and monitoring systems are constructed. Early civil infrastructure control and monitoring systems employed a centralized computing model for sensor processing and actuator control. These systems required extensive wiring to route power, sensor, and control signals among the distributed input and output devices. Furthermore, the operation of the entire system depended on one or two computers. Abstractly, these civil infrastructure applications are a realtime data acquisition and control system. Due to the dramatic decrease in computing costs, it is now feasible to construct these real‐time systems using dozens or even hundreds of distributed processors linked with a data communication network. This allows the controllers to be located adjacent to sensors and actuators, thereby reducing the need for long lengths of multiconductor wire that is subject to noise and breakage. Also, failure of a single processor does not necessarily cause the entire system to fail. This paper introduces the reader to a technology called LonWorks for constructing distributed sensing and control systems. The LonWorks technology is essentially a data communication network that links together extremely small computers called Neurons. Particular emphasis is placed on describing the communication architecture and emphasizing how the distributed Neuron communication processors are designed to ensure a truly modular and open architecture.

An 8-channel counter and histogramming sub-module: the basic building block for fast real-time data acquisition systems

This paper presents an 8-channel counter and histogramming sub-module with local memory which in association with a dedicated motherboard and bus system forms a fully expandable data acquisition system. As a first application, the authors sued this sub-module to implement a 16-input Calibration Channel Unit module to carry out the acquisition of real-time calibration data (beam intensity, sample temperature...) for time-resolved Synchrotron Radiation experiments. This sub-module will also be used as the basis of the data acquisition system for the new fast wire per wire X-ray detector.

Real time signal processing for high-frequency long distance crosswell tomography

Acoustic crosswell tomography was used for determining the sediment porosity, permeability, and shear strength from travel-time measurements by means of travel-time inversion and rock mechanics [Yamamoto etal., Geophysics (1994) (1995)]. These properties can be used to model the propagation and scattering of acoustic waves in saturated sediments. Due to the effects of intrinsic attenuation, transmission loss, and scattering, crosswell measurements usually are limited to ranges of 50–100 times the wavelength of the signals. It was believed that the diffusive nature of scattering put the coherent limit of acoustic wave propagation in sediments at approximately 1000 wavelengths. To extend the measurements of the propagation of acoustic waves to longer ranges, a real time processing and data acquisition system was employed. A crosswell tomography experiment with a crosswell distance of 540 m was performed at a limestone aquifer at Sanibel Island, Florida. Pseudorandom binary sequences modulated with carrier frequencies up to 6 kHz, which puts the range around 1400 wavelengths, were successfully transmitted by using pulse compression and coherent averaging techniques. The hydraulic structure of the Earth with a cross section of 540 m×150 m has been imaged at spatial resolution of a few meters. [Work supported by ONR.]

Computer‐Aided, Single‐Specimen Controlled Bending Test for Fracture‐Kinetics Measurement in Ceramics

Fracture testing of ceramics by using controlled crack growth is proposed to allow study of crack‐kinetics behavior under a given loading history. A computer‐aided, real‐time data acquisition system improves the quality of crack‐growth parameters obtained in a simple, single‐specimen bend test. Several ceramic materials were tested in the present study: aluminum nitride as a linear‐elastic material; and alumina and yttria‐stabilized zirconia, both representative of ceramics with microstructure‐dependent nonlinear fracture properties. Ambiguities in the crack‐growth diagrams are discussed to show the importance of accounting for crack‐growth history in correctly describing nonequilibrium fracture behavior.

In-situ prediction of reactive ion etch endpoint using neural networks

Reactive ion etching (RIE) in radio frequency glow discharges is perhaps the most popular means of achieving the level of detail necessary to pattern small geometry features in electronics manufacturing. However, the complexity of the RIE process has prompted the use of empirical models utilizing neural networks, which offer advantages in both accuracy and robustness over statistical methods. In this paper, a neural network trained to model the correlation between DC bias and etch rate was used to predict the time required to remove a specified thickness of silicon dioxide (SiO/sub 2/) in a CHF/sub 3//O/sub 2/ plasma. A real-time data acquisition system that transmits process conditions from a Plasma Therm 700 series RIE system was used to monitor DC bias during etching. A back-propagation neural network was trained to predict the amount of time required to etch the remaining amount of film while in the midst of etching. Inputs to the network included elapsed time during the etch run, the desired etch depth, gas flow rates, chamber pressure, and RF power. This network exhibited a 26 s RMS error on training data, and predicted the process endpoint on a set of test etch recipes with an average error of less than two minutes for a process time of about 25 min. >

An heterogeneous and distributed architecture based on a reflective memory interconnection network

Complex control system architectures are usually characterized by the heterogeneity and the distribution of their technological components. Besides, system engineers have at their disposal a number of technological alternatives to implement any of the different parts of a distributed application. For those reasons, the communication among the distributed components of a system often becomes an issue to address. In this paper we report a technique to solve this problem which is based on the use of reflective memory devices without any additional software requirement, and that can satisfy hard throughput requirements. We describe the implementation of a testbed for testing the proposed communication technique. We finally apply the results to a real-time data acquisition system characterized by a very heterogeneous architecture, whose components have been pushed to the limits of their performance and capacity.

305 PRESSURE OF SAP EXUDATE OF TOMATO PLANTS IN VARIED ROOT ENVIRONMENTS

Sap pressure of cut tomato stems was monitored using a real time data acquisition system to assess changes in the root zone environment. Hydroponically-grown tomato plants were cut and a gas-free connection made to a temperature-compensated pressure transducer. When plants were bathed in nutrient solution under isothermal conditions, pressure increased to a maximum within 10 to 75 min; maxima varied in the range of 20 kPa to 150 kPa. A fatigue phenomenon occurred with all plants, exhibited by decreases in pressure maxima over time. When root zone aeration was stopped or a nitrogen atmosphere was used, pressure dropped following a lag of about 30 min. This decrease in pressure was partially reversible when aeration was resupplied. Near instantaneous changes in sap pressure occurred when the root zone was manipulated by imposing a temperature gradient or by increasing the osmolarity of the solution. The technique reported may be useful for continuous monitoring of changes in the root zone environment and in assessing plant health.

A knowledge based system using fuzzy inference for supervisory control of bioprocesses

In this paper, a rule-based, real-time knowledge based system for bioprocess fault diagnosis and control is described. The system was designed to generate on-line advice for the operators and to supervise automatic control of bioprocesses, using biotechnical production of lactic acid as an example process. It consists of a real-time data acquisition and data processing system linked to a fuzzy expert system written in Smalltalk V/Mac. The expert knowledge was expressed in the form of a rule-based knowledge network, fuzzy membership functions and control strategies. The fuzzy expert system carries out on-line fault diagnosing on the basis of filtered specific rates calculated from process variable measurements, and provides suitable countermeasures to recover the process. Fault diagnosis was realized both by backward and forward chaining procedures. The system was constructed to allow three different control strategies (given here in Smalltalk syntax), change of Setpoint, FuzzyAnswer for each discovered fault, employing the fuzzy mean defuzzification method, and linguistic Advice to the operator. The system was successfully tested on-line with a laboratory scale process.

Multichannel real-time data acquisition system using dual ported FIFO buffers

In contrast to real-time data acquisition systems employing a minicomputer with a real-time multiprogramming operating system, this paper describes the design and development of a high throughput data acquisition system using an IBM compatible PC/AT, high speed sampling A/D converter, and dual ported FIFO RAM buffers, in the MS-DOS environment. Data acquisition software is developed in Turbo Pascal with a few in-line machine language procedures.

A UNIX-based real-time data acquisition system for microprobe analysis using an advanced X11 window toolkit

A real-time data acquisition system for microprobe analysis has been developed at the Free University of Amsterdam. The system is composed of two parts: a front-end real-time and a back-end monitoring system. The front-end consists of a VMEbus based system which reads out a CAMAC crate. The back-end is implemented on a Sun work station running the UNIX operating system. This separation allows the integration of a minimal, and consequently very fast, real-time executive within the sophisticated possibilities of advanced UNIX work stations.

Design and development of a biomechanical apparatus to test the integrity of the Luque orthopaedic internal bone-plate fixation system.

This paper describes the design and construction of a biomechanical model that will determine the pull-out strengths and fatigue failure of internal fixation devices used at the lumbosacral junction. Fusions at this junction have the highest failure rate. It is suggested that devices that successfully fix this vertebral unit will be effective at other levels of the spine. A model that tests any device designed for use at the lumbosacral junction will therefore provide a uniform measure of the effectiveness of different kinds of instrumentation at the L5-S1 vertebral unit. It will also provide predictive values for fixation systems at other spinal levels. A real-time data-acquisition system was also designed and used to define and determine the failure of the Luque orthopaedic bone-plate fixation device.

Anordnung zur Aufzeichnung und sofortigen Interpretation der myoelektrischen Aktivität des Magens — Elektrogastrographie — Computer-aided Measurement and Interpretation of the Myoelectrical Activity of the Stomach

Unlike other electrophysiological measurements such as electrocardiography (ECG) and electroencephalography (EEG), the cutaneous measurement of the electrical activity of the stomach (electrogastrography, EGG) is not an established clinical diagnostic procedure. To overcome common problems in acquiring very-low-frequency signals in the presence of large and unstable voltages we developed a real time data acquisition and analysis system based on linear-phase digital signal processing instead of analog filtering. FFT's computed on line from highly overlapping time sets are displayed as pseudo-3D or grey-scale graphic plots.

Hysteresis characteristic analysis of transformer under different excitations using real time measurement

A simplified method for the analysis of hysteresis characteristics in a transformer under nonsinusoidal excitation is discussed. The nonsinusoidal sin m (wt) waveforms are used in the experiments. The hysteresis analysis is treated as a shape identification problem and is solved using the piecewise curve fitting technique. The proposed method uses a real-time data acquisition system, for measurement data and calculates hysteresis loop and loss directly from those data. Expressions for the hysteresis loop and energy loss using the proposed method are shown to agree well with analog measurements. The discrepancy between these two methods is less than 0.65%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimal estimation of layback distance for marine towed cables

The estimation of towfish layback distance is usually performed with computer programs that implement numerical integration of system differential equations. The system dynamic model usually includes an estimate of coefficients of drag and velocities of the towfish and cable. Often these quantities are unknown or estimated with a great deal of uncertainty. The technique reported uses an optimization approach to circumvent the estimates of critical parameters and instead uses accurate measurements of towfish depth and length of cable paid out. A criterion is formulated and minimized using a simple gradient-optimization method. The simulation results indicate that the method works well and can be implemented in a real-time data-acquisition system. >

Real-time Seismic Amplitude Measurement (RSAM): a volcano monitoring and prediction tool

Seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions. Although several real-time earthquake-detection and data acquisition systems exist, few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent. Analog seismic records provide a quick visual overview of activity; however, continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders. At the Cascades Volcano Observatory, an inexpensive 8-bit analog-to-digital system controlled by a laptop computer is used to provide 1-min average-amplitude information from eight telemetered seismic stations. The absolute voltage level for each station is digitized, averaged, and appended in near real-time to a data file on a multiuser computer system. Raw realtime seismic amplitude measurement (RSAM) data or transformed RSAM data are then plotted on a common time base with other available volcano-monitoring information such as tilt. Changes in earthquake activity associated with dome-building episodes, weather, and instrumental difficulties are recognized as distinct patterns in the RSAM data set. RSAM data for domebuilding episodes gradually develop into exponential increases that terminate just before the time of magma extrusion. Mount St. Helens crater earthquakes show up as isolated spikes on amplitude plots for crater seismic stations but seldom for more distant stations. Weather-related noise shows up as low-level, long-term disturbances on all seismic stations, regardless of distance from the volcano. Implemented in mid-1985, the RSAM system has proved valuable in providing up-to-date information on seismic activity for three Mount St. Helens eruptive episodes from 1985 to 1986 (May 1985, May 1986, and October 1986). Tiltmeter data, the only other telemetered geophysical information that was available for the three dome-building episodes, is compared to RSAM data to show that the increase in RSAM data was related to the transport of magma to the surface. Thus, if tiltmeter data is not available, RSAM data can be used to predict future magmatic eruptions at Mount St. Helens. We also recognize the limitations of RSAm data. Two examples of RSAM data associated with phreatic or shallow phreatomagmatic explosions were not preceded by the same increases in RSAM data or changes in tilt associated with the three dome-building eruptions.

Real-time digital control, data acquisition, and analysis system for the DIII-D multipulse Thomson scattering diagnostic

A VME-based real-time computer system for laser control, data acquisition, and analysis for the DIII-D multipulse Thomson scattering diagnostic is described. The laser control task requires precise timing of up to eight Nd:YAG lasers, each with an average firing rate of 20 Hz. A cpu module in a real-time multiprocessing computer system will operate the lasers with evenly staggered laser pulses or in a ‘‘burst mode,’’ where all available (fully charged) lasers can be fired at 50–100 μs intervals upon receipt of an external event trigger signal. One or more cpu modules, along with a LeCroy FERA (fast encoding and readout ADC) system, will perform real-time data acquisition and analysis. Partial electron temperature and density profiles will be available for plasma feedback control within 1 ms following each laser pulse. The VME-based computer system consists of two or more target processor modules (25 MHz Motorola 68030) running the VMEexec real-time operating system connected to a Unix-based host system (also a 68030). All real-time software is fully interrupt driven to maximize system efficiency. Operator interaction and (non-real-time) data analysis takes place on a MicroVAX 3400 connected via DECnet.

Real time data acquisition system for very high energy gamma ray astronomy experiment

An experiment is being conducted at Pachmarhi (MP) to search for TeV gamma rays from celestial sources like: Cygnus X-3, Crab Pulsar, Cas-γ, Her X-1 etc. The detection of an extensive air shower intiated by TeV γ-rays or more abundant cosmic-ray photons in the Earth's atmosphere is through the Cherenkov light from the secondaries (e + and e −). It is identified by multiplicity logic of the signals from an array of parabolic mirrors (or a group of mirrors called a bank) at the foci of which a fast (RCA 8575) phototube is placed. Whenever such an event occurs, we record the time of occurrence correct to a microsecond, the scalers which record various counting rates, the latch information signifying which mirrors or banks have triggered during the event, the pulse height in each phototube to be read from a CAMAC ADC module and the relative time delays between various mirrors or banks from a CAMAC TDC module. The event rate is in the range of 2–20 Hz. This is accomplished by an indigenously designed hardware system built around a Q-bus-based PDP 11/23 processor through a general-purpose 16-bit parallel I/O interface, viz. DRV-11. High-priority interrupt (INTA) is used for the event while lower-priority interrupt (INTB) is used by the monitor interrupt generator (MIG). A versatile software package called HEGROSOFT has been developed to control the above hardware acquisition system. It is designed to meet the following objectives with four-level task priorities: (a) to acquire the γ-ray event data with a recording dead time of ∼ 1 ms; (b) monitor the various counting rates and print them out at regular intervals; (c) attend to the operator interrupt service requests from the console; (d) provide services for a low-priority job queue to make use of the idle time of the processor. The complete acquisition system and its design philosophy are explained in detail.

Real-time computer control of a flexible spacecraft emulator

A description is given of a ground-based test facility named Daisy, which was established to study control issues for large flexible spacecraft. The validation of modern algorithms for system identification and shape and attitude control and the development of new control devices can be performed using Daisy. The experimental structure consists of a radial mesh of ribs attached flexibly to a rigid hub. The structure is instrumented with position and rate sensors and controlled by a real-time computer and data acquisition system by means of torque actuators. The more important aspects of these subsystems and their integration are presented along with experimental results for a baseline controller, consisting of a simple integral-derivative feedback control on the position of the hub. >

The Aleph data acquisition system

Aleph is one of the four large high-energy physics experiments being completed for the LEP (Large Electron Positron) accelerator at CERN. Several hundred thousand detector elements deliver some 500 Mbytes of raw data per second. The author briefly describes the accelerator and the Aleph detector. He then discusses the design and implementation of the multilevel real-time data reduction and acquisition system, covering the requirements, the readout architecture, its implementation, data reduction, aspects of the detector-specific front-end electronics, and Aleph's present status and performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Real-time data acquisition system for laser and radio frequency spectroscopy

A low-cost real-time data acquisition system utilising a master (PC-XT) and a slave (Z80) computer for high-resolution atomic spectroscopy is described. The master and the slave computer are linked by a high-speed parallel FIFO buffer permitting data acquisition on a fixed time schedule with 4 mu s time resolution. A modular interface box allows the system to control complex spectroscopic experiments. The use of commercial software packages allows fast and efficient data reduction and analysis on the same computer system. The performance of the system has been demonstrated in polarisation spectroscopy experiment on zirconium.