IEEE Transactions on Nuclear Science, Vol. NS-34, No. 4, August 1987

OPERATING APPLICATIONS OF A NETWORKED DATA ACQUISITION SYSTEM

Rodney TaylorInterfield Research Associates (as above)

General Dynamics -- Pomona Division, P.O. Box 2507, Pomona, CA 91769(7114)868-4099

Jonathan D. Melvin, Ph.D.Interfield Research Associates, 2314 La Mesa Drive, Santa Monica, CA 90402

(213)395-5841California Institute of Technology, Mail Stop 104-44, Pasadena, CA 91125

(818)356-4126

Scott TaylorDouglas Engineering, 402 21st Place, Santa Monica, CA, 90402

(21 3)394-4026

Summary. This paper describes operatingapplications of a networked data acquisition computersystem which has met the needs of researchers in avariety of scientific disciplines. The networksoftware system, called IRANET (Interfield ResearchAssociates Network Software System), has beeneffectively used in nuclear physics, plasma physics,aeronautical engineering, and semiconductor processinglaboratories.

Introduction

The data acquisition hardware of the systemconsists of one or more DEC LSI-11 satellite computersrunning the RT-11 operating system networked to a hostcomputer. The host computer may be a DEC VAX,mnicroVAX, or VAXstation running VMS. The satellitecomputers commonly use CAMAC crate data acquisitioninterfaces. However, a DEC KXJ single-board computerslaved to a DEC LSI-11 can also be used. The computersare connected with either DEC or Interlan Ethernetinterfaces to standard transceivers and coaxial cables.The DEC DELNI can be used in place of a coaxial cablewhen eight or fewer computers are to be connected.

The data acquisition software includes networksoftware designed for fast data transfer. In addition,interactive, menu-driven software has been developedfor simple control of the system by the user. Allsystem control, including control of one computer bythe other over the network, uses a flexible,easily-configured data structure.

The data acquisition software has been used forseveral years in a variety of physics and engineeringlaboratories. The following sections describe how thisone software system has been successfully applied tosuch diverse tasks as plasma physics, nuclear physics,and testing of gigahertz microwave devices. Anotherpaper in this volume titled "Performance of anIntegrated, General-Purpose Networked Data AcquisitionSystem" presents performanice data on the software.

The Demands on a Modern Data Acquisition System

Most data acquisition systems must be fast in oneof two ways: Either the system must quickly servicefrequently-occurring external events called interrupts,or it must rapidly transfer large quantities of datafollowing less frequent events. The performance of anydata acquisition system is measured by how well itaccomnplishes one or both of these tasks.

Besides being fast, a data acquisition system inustbe capable of sophisticated data analysis. A usefulsystem anust collect data, perform complex rnathematicalanalysis, display graphical results, and transfer datato archival storage while an experiment is in progress.

The data acquisition system described hereperforms all of these tasks quickly and easily becauseit does not rely on a single computer. The fact thatthe system is networked allows its high performance,flexibility, and ease of use. In addition, because thesystem contains both 16-bit and 32-bit computers, ithas the fast interrupt capability of the 16-bitcomputer and the powerful data analysis capability ofthe 32-bit computer. No single computer system canoffer this double performance advantage.

Applications of The Networked Data Acquisition System

The following applications of the networked dataacquisition system illustrate how a single system cansatisfy the diverse requirements of modern dataacquisition.

Semiconductor Laboratory Applications

The networked data acquisition system has beenused for data collection and process control at theGeneral Dynamics Pomnona Division Gallium ArsenideLaboratory since 1985. In this laboratory, real-timeinterrupt demands are not great, but large quantitiesof data must be collected. The Gallium ArsenideLaboratory has a microVAX-II workstation networked totwo LSI-11/73 computers. The LSI-11 computers are usedas data-collection and process-automation satellites.The MicroVAX is used for central data archiving and forprocess control. Each LSI-11 is connected to a CAMACcrate with a Kinetic Systems 3912 or 3920 cratecontroller.

One LSI-11 and CAMAC crate is used to testmicrowave and millimeter wave Gallium Arsenide (GaAs)devices. This satellite is interfaced to a largevariety of General Purpose Instrumentation Bus (GPIB)equipment through the CAMAC crate. In addition, thereare several digital-to-analog, analog-to-digital, anddigital-only input/output modules in the crate used tocontrol and monitor device tests.

One useful application of the data acquisitionsystem in the Gallium Arsenide Laboratory is acapacitance-voltage (C-V) profile test setup. Thisapplication, fully implemented in only three days,provides valuable information about GaAs materialquality. The application was sirnple to develop and iseasy to use. In addition, it operates an order ofmagnitude more quickly than the HP-9836 C-V datacollection system which it replaced.

The second LSI-11 and CAMAC crate is used tocontrol an ultra-high vacuum molecular beam epitaxy(MBE) system. Special hardware was built by DouglasEngineering to replace several items originallysupplied by the MBE system manufacturer. With this

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special hardware and the networked data acquisitionsystem, the MBE system is completelycomputer-controlled. This automation of the MBE is inthe final stages of implementation. When the system iscomplete, it will simultaneously monitor tentemperature sources, two vacuum gauges, an ion massspectrometer, and the state of eight shutters. Duringeach epitaxial growth in the MBE system, which requiresup to eight hours, all of the growth parameters will becontrolled and logged.

Plasma Physics Research

The UCLA Plasma Physics Laboratory uses thenetworked data acquisition system to control plasmaphysics experiments and to collect data from severaldiagnostic probes. Ultra-fast transient recorders areused to collect data from a UCLA-developed probe whichmeasures plasma particle velocities over a very smallsolid angle. The particle velocity distribution ismapped throughout a large three-dimensional region inthe plasma. In addition, the magnetic field ismeasured throughout the region.

Monitored events occur every 1.5 seconds, for aperiod lasting hours or days. The satellite computermoves the data to a host VAX computer and operatesstepping motors which position the diagnostic probes inthe plasma. The host computer archives the data andcarries out filtering and analysis with the help of anarray processor. It is not uncommon to acquire morethan one hundred megabytes of data during a singleexperiment.

Laser Doppler Velocimetry

The Aeronautics Laboratory at the CaliforniaInstitute of Technology uses the network software toperform sophisticated real-time laser dopplervelocimetry data analysis. A LSI-11 satellite computeruses external electronics to measure the modulation ofintersecting laser beams within a volume of movingfluid. Particle velocity is measured at the pointwhere the laser beams intersect. By moving theintersection point throughout a volume, three

dimensional distributions of turbulent flow aredetermined.

The satellite computer sends data buffers over thenetwork to a VAX host computer for analysis. The hostquickly performs fast-Fourier transforms and spectralavaraging, and then sends the analyzed data back to thesatellite for plotting. In this way, the experimenteruses the network to make prompt data analysis possible.

Experimental Nuclear Physics

The W.K. Kellogg Radiation Laboratory at Caltechand the Nuclear Structure Research Laboratory at theUniversity of Rochester both use the networked computersystem to perform time-critical experiments. In theseapplications, particle collision and disintegrationevents are detected with trigger circuits, measuredwith analog-to-digital converters, and acquired withLSI-11 satellite computers through CAMAC interfaces.

During nuclear data collection, the satellitecomputer must respond to events at kilohertz rates.Each time an event occurs, satellite computer programsreceive data through CAMAC interfaces and store them indata buffers. When the data buffers fill, data aretransferred over the network to VAX host computers.The host computers perform real-time data analysis andstore original and analyzed data on disk or tape.

Conclusion

The four preceeding examples of operatingnetworked data acquisition applications illustrate avery important point: A single networked computersystem can meet any requirement of a modern dataacquisition application.

By using a versatile high-performance networkconfiguration, the advantages of several differentcomputers can be combined in a single data acquisitionsystem. Specifically, the ability of the LSI-11computer to service interrupts quickly can be combinedwith the ability of the VAX computer to process largequantities of data.