No. 9262 |P8 I ■ - 1 mSm PS WB1HM I B8WBWDf»ti«BB»ai Bg l 8PW w ™ flBH)Pe8BSiSi 1 ■:- Sfe* ft SsSKS «§§■§ ;;■ : t- ;=;.?;'>;■ i i kHbhSbSbs pBRJSaa k> ■! ||||g|3Hgg Hill ffisassEji MM II mm aEmm ! .'■:■-.■- ^V ^'> °o # ^ A.V t!^» ^ V »!*•* *>». .4.9 >* .i^ 0>^ ?V <, ••••.•>*' V*^V V*— ; >* V^> v T --* 4 «r X w /%. ** v ^ > o^ V*^> v-rav> V™V V^/ V^V V ^"> " « ° A$ '^^ W * o *9^ ^* r / % •. ^ cT . **t. ,*•'.'•• ♦•' ^^^\y °^^v*/ V*^\/ °o**^> , %P° ^'•.-« #■ ' /»K'. %.„«.' ;^& \„S #*k- \^ .v^i-. V./ .£«£• V„. c .v^Mr- &, *•«'* A V * «i> *•■•' aT '9a. **..i»* aP ft**!* 1 •L^L'. >» '.«•' . ■?> * 4 V V »bv* L* .■ *bV* * v *v VV /% * V *V ■•/► A > . . . 'Cs < mSm: «b>* ;ra^ ^ * A 4, *a6s.^.' *r*. a** *.JlvUr7^«* A <* **(?^J^ • *P*. a*' ♦^K'B^ 1 ^** .a a » \S : '..' A ***** .♦ o 9262 BUREAU OF MINES H\3 INFORMATION CIRCULAR/1990 Computer-Automated Measurement- and Control-Based Workstation for Microseismic and Acoustic Emission Research By F. M. Boler and P. L. Swanson «?* w % 80 \ YEARS g **AU OF ^ o ¥ U.S. BUREAU OF MINES 1910-1990 THE MINERALS SOURCE Mission: As the Nation's principal conservation agency, the Department of the Interior has respon- sibility for most of our nationally-owned public lands and natural and cultural resources. This includes fostering wise use of our land and water resources, protecting our fish and wildlife, pre- serving the environmental and cultural values of our national parks and historical places, and pro- viding for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also promotes the goals of the Take Pride in America campaign by encouraging stewardship and citizen responsibil- ity for the public lands and promoting citizen par- ticipation in their care. The Department also has a major responsibility for American Indian reser- vation communities and for people who live in Island Territories under U.S. Administration. Information Circular 9262 ! Computer-Automated Measurement and Control-Based Workstation for Microseismic and Acoustic Emission Research By F. M. Boler and P. L. Swanson UNITED STATES DEPARTMENT OF THE INTERIOR Manuel Lujan, Jr., Secretary BUREAU OF MINES T S Ary, Director Library of Congress Cataloging in Publication Data: Boler, Frances M. Computer-automated measurement- and control-based workstation for micro- seismic and acoustic emission research / by F. M. Boler and P. L. Swanson. p. cm. - (Information circular / Bureau of Mines; 9262) Includes bibliographical references. 1. Rock bursts-Forecasting-Data processing. 2. Microseisms-Measurement- Data processing. 3. Microcomputer workstations. I. Swanson, P. L. (Peter L.) II. Title. III. Series: Information circular (United States. Bureau of Mines); 9262. TN295.U4 1990 [TN317] 622 s-dc20 [622'.28] 90-1943 CIP CONTENTS Page Abstract 1 Introduction 2 Acoustic emission-microseismic workstation 2 Data acquisition hardware 3 Trigger circuitry 4 Computer hardware 4 Data acquisition software 5 Data analysis software 5 Summary 9 References 9 ILLUSTRATIONS 1. Microseismic activity at hardrock mine 2 2. CAMAC data acquisition workstation 3 3. CAMAC crate 4 4. Process flow diagram 6 5. Example of monitor display of microseismic event 7 6. Three-dimensional graphics display 8 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT Hz hertz Mb megabyte Kb kilobyte MHz megahertz kHz kilohertz s second m meter COMPUTER-AUTOMATED MEASUREMENT- AND CONTROL-BASED WORKSTATION FOR MICROSEISMIC AND ACOUSTIC EMISSION RESEARCH By F. M. Boler 1 and P. L. Swanson 1 ABSTRACT The U.S. Bureau of Mines has configured a flexible data acquisition and analysis workstation, which incorporates control and analysis software written in-house for use in mining research experiments conducted in the laboratory and in operating underground mines. This data acquisition system combines computer-automated-measurement-and-control (CAMAC) modular instrumentation with a Unix-based graphics workstation. The data acquisition front-end hardware can be interfaced to almost any computer. CAMAC instrumentation modules adhere to mechanical, electrical, and digital interface standards and can be custom designed or purchased off the shelf. Communications along the CAMAC bus are regulated by the crate-controller module, which contains the only hardware link to the computer interface. Software support for the data acquisition and analysis workstation consists of a series of functions and programs written in the "C" programming language designed to provide flexible and fast data acquisition, processing, and analysis. The user can interactively control the digitizers and other CAMAC modules by sending standard CAMAC read, write, and command function codes from a menu- driven program. Automated data collection is achieved through software that responds to hardware interrupts triggered by acoustic emission or microseismic events. Graphics display routines are used to plot part or all of the data and provide the ability to process and store signal information selectively. ^eophysicists, Denver Research Center, U.S. Bureau of Mines, Denver, CO. INTRODUCTION To mitigate hazards associated with rock failure in underground mines, the U.S. Bureau of Mines conducts investigations of rock failure behavior both in laboratory- scale tests and in direct monitoring at underground mines. In this Bureau report, a CAMAC-based data acquisition system is described, which is used to study mine and laboratory rock failure problems. Rock bursts are abrupt rock mass failures within mines that cause damage to the mine workings. Rock bursts have been observed to be related to the patterns of micro- seismic events in time and space (I). 2 Rock bursts and other microseismic activity are a consequence of the inter- action of the mining extraction process with the existing geologic structure and the ambient stress field. Figure 1 shows microseismic events generated in response to routine mining activity near a metal ore vein, which is offset several meters by a steeply inclined fault (Coeur d'Alene district, northern Idaho). The microseismicity patterns illustrate the influence that certain fault structures can have on the mechanics of deformation in the mining environment. Individual microseismic events are a manifestation of the rock structure-mine geometry-stress interaction leading to a variety of modes of rock failure. Both the time-space pattern of microseismic events and the seismic waveforms contain information about the processes involved in failure. To retrieve the information from waveforms at individual accelerometers, the entire waveform of the seismic signals must be recorded. Then, in a manner equivalent to seismogram analysis for earthquakes, mine-related microseismic activity can be analyzed to obtain the event location and focal mechanism (orientation of the fault slip plane and slip direction). The spectral content of the waveforms can be analyzed to obtain stress drop, rupture strength, and source dimensions. LEGEND Microseismic events — 4300 level --- 4600 level ^b Ore vein \ Faul t strike **** Instrumentation borehole (4300) o 10 Scale, m Figure 1 .-Microseismic activity at hardrock mine. A, Plan view of 4300 and 4600 levels (1 ,300 and 1 ,400 m) below surface at the study site; B, microseismic activity near 4300 level, which indicates activation of preexisting fault The same methods of analysis can be applied to microcrack-scale failure events (acoustic emissions), which occur in laboratory rock specimens under stress. To cap- ture and analyze the typically large numbers of events (perhaps hundreds per day in a given mine working area or hundreds per hour in laboratory acoustic emission work), computer control of digital data acquisition and semiautomated computer processing and analysis at the underground fieldsite or in the laboratory is necessary. A workstation with these features has been configured, con- trol and analysis software has been written, and both have been tested in a field situation. ACOUSTIC EMISSION-MICROSEISMIC WORKSTATION Five fundamental requirements were involved in the selection of hardware for the acoustic emission (AE)-microseismic (MS) workstation. These were the ability to (1) acquire multichannel (e.g., 32 channels) microseismic data at sampling rates of 100 kHz per chan- nel and event rates of several tens of events per minute; (2) manage multichannel (e.g., 8 channels) AE-data acqui- sition at sampling rates of 10 MHz or more per channel and event rates of several events per second; (3) acquire quasi-static measurements of stress, displacement, and other physical parameters on an arbitrarily large number of additional channels; (4) acquire, display, and analyze data in a multiuser, multitasking environment. The fifth Italic numbers in parentheses refer to items in the list of references at the end of this report. requirement was that the hardware had to be rugged, reli- able, compact (able to fit into a single standard equipment rack), and transportable. Although there are computer systems with data acquisition boards that incorporate char- acteristics capable of accomplishing requirements 1, 3, 4, and 5, no affordable, easily expandable system was found to be capable of handling the high analog-to-digital (A-D) conversion and data transfer rates of requirements 1 and 2 simultaneously, and meet requirement 5 as well. A sys- tem capable of performing as required, comprised of three essential components, was configured. These components are (1) a CAMAC system for signal conditioning, A-D conversion, and short-term data storage; (2) a trigger circuit; (3) a computer graphics workstation for communi- cation with the CAMAC and data analysis. Each of these components is discussed in greater detail. DATA ACQUISITION HARDWARE CAMAC instrumentation hardware was selected for a variety of reasons, a major one being its modularity. CAMAC instrumentation was originally developed for experiments performed in the nuclear physics field (2); it is a well-established technology. CAMAC modules, manu- factured by over 50 companies, adhere to international digital interface and modular instrumentation standards (3). A CAMAC module is any circuit board of nearly any function (A-D conversion, memory, signal conditioning, stepper motor controller are examples) that is built to slide into a CAMAC crate. The CAMAC crate supplies power and a backplane (CAMAC bus) for intermodule and CAMAC-to-computer communication. Modules from various manufacturers easily function together in a CAMAC crate under computer control. The specific computer model and the interface used are not dictated by the CAMAC system, although the crate controller generally must be selected with the computer interface capabilities in mind. The requisite range of digitizing rates (10 Mhz for AE, 100 kHz for MS) is readily obtained by a selection of appropriate A-D conversion modules. Additional channels and memory for A-D conversion are easily incorporated. As improved modules are developed, the system can be upgraded. Also, user-developed circuitry can be incor- porated into custom CAMAC modules. Figure 2 shows the CAMAC and computer hardware configured for the MS and AE experiments. The system is currently configured for 32 accelerometers sampled at up to 100 kHz per channel with 12-bit resolution, with a 1-megasample (2-Mb) memory for MS monitoring and for 8 AE transducers at up to 20-MHz sampling rate per channel with 8-bit resolution with 8-kilosample memory per channel. The AE and MS data acquisition transfer cycle is started upon receipt of a stop trigger from cir- cuitry that is separate from the CAMAC system. Trigger Tr igger logic Programmable gai n amp I i f iers 12-bit ADC 100 kHz/ channel Microsei smic transient recorder control ler 9 Local memory 1 mega- sample Multi- channel DVM CAMAC BUS. IEEE-488 CAMAC bus control ler Hard disk 3-D color graphics moni tor CPU 16 Mb RAM 6803C processor UNIX IEEE-488 Other graphics terminals Tape storage Figure 2.-CAMAC data acquisition workstation for AE-MS full-waveform capture, stress-displacement measurement, and data analysis and display. DVM-dlgltal voft meter, LAN-local area network, ADC-analog-to-digital conversion, CPU-computer processing unit, RAM-random access memory, UNIX-operating system. (IEEE-488 is also known as GPIB.) circuitry inputs are analog accelerometer signals (MS) or ultrasonic transducer signals (AE). In general, part of the signal before and after the first arrival is captured on all channels by controlling the relative amounts of pre- and post-trigger recording. The system is configured with a a general purpose interface bus (GPIB) interface for computer-CAMAC communication (4). Additional mod- ules for signal conditioning and for quasi-static rock mechanics measurements of loads and displacements are configured with this system. The present configuration of the instrumentation modules and CAMAC crate is shown in figure 3. Multiuser access to the crate is also possible. For example, one user can monitor rock mechanics instru- mentation while another monitors the MS acquisition. Also, processor priority and interface locking are features of the operating system (Unix) and the interface library software, so that multiple processes accessing the crate can be in action concurrently. TRIGGER CIRCUITRY The external trigger circuitry used for the MS data acquisition is a modification of the design by Sonder- geld (5). This circuitry provides a transistor-transistor logic (TTL) pulse to the microseismic transient recorder controller (fig. 2). Noise discrimination is accomplished in three ways. First, the signal frequency must exceed a certain set frequency. This prevents triggering by distant events that are unrelated to the study area and by low frequency mining production noise. Second, the signal must contain a minimum number of cycles. This allows elimination of certain electromagnetic noise signals, which are typically of short duration and few cycles relative to MS events. Third, as currently configured, up to four channels can be required to meet the discrimination criteria with a minimum delay time between arrivals at each channel. This guarantees that non-EM signals be large enough to trigger up to four channels. The dead time between triggers is also adjustable. A similar configuration of AE triggering is possible. A means of insuring that all AE channels receive the stop trigger at the same time (within some tolerance) would need to be added to the circuitry described previously. COMPUTER HARDWARE The multitasking acquisition and analysis environment is provided by a Motorola Corp.-68030 based Unix work- station (fig. 2). The system is configured with 16 Mb of random access memory (RAM), and a 130-Mb hard disk drive. For display of microseismic event locations and I I % <§ # • & m ■*. * * ^H % <% • * • • * - s - t # S> # & # • * 8 * • • * * * « * 8 y ft « ; & « i » » » ; # 8 * * 9 * ^ * * • • j •** • * 1 » # » a » » # * » a a ^ i* & 1 # * ; « * * © • • • # • : • « 0' ' '0 m Wfl «►■ & W ' } j : tim m WOimHogy Figure 3.-CAMAC crate configured with acoustic emission, microseismic, and signal conditioning modules. focal mechanisms overlaid on mine structure and geology, a hardware graphics accelerator is utilized. This allows examination of data in three dimensions with a continuous- ly variable point of view, greatly enhancing the ability to make correlations of microseismic activity with mine structure and geology. An important aspect of a research-grade multichannel full-waveform microseismic system is the ability to archive large quantities of data for later analysis. During field acquisition, the unattended tape storage capacity of the system is 536 Mb or about 10 typical days' worth of data. DATA ACQUISITION SOFTWARE The software developed in-house 3 for data acquisition is menu-driven. The program accomplishes its tasks via function calls that send instructions to and receive data from the CAMAC. Some of these function calls are also configured as system level commands. Figure 4 shows a general process flow diagram for data acquisition. One of the main tasks of the program is configuring the CAMAC modules. For the A-D converters, configuration parameters include number of channels, number of 8-bit (AE) or 12-bit (MS) samples per channel, sampling rate, number of pretrigger samples to retain, and individual channel gains for the signal conditioners. CAMAC con- troller parameters include data transfer mode (block mode transfer versus word-by-word transfer) and individual module lockout (from system interrupt capability). When an event occurs, the trigger circuitry issues the stop trigger to the continuously sampling CAMAC trans- ient recorders. (A stop trigger for the converters can also be sent using software control.) Once triggered, the CAMAC controller module, which oversees transmissions on the CAMAC bus, notifies the computer that data are ready for transfer. Typically, the program is setup to monitor the CAMAC in the background. This allows other tasks, such as plotting or event location to take place in the foreground. The background program, which has the highest processor priority, handles transfer of data from CAMAC to memory and then to disk files (demulti- plexing channels if necessary in the process), followed by re-arming of the A-D converters for the next microseismic event. It takes 2 to 3 s to transfer a 200 Kb event from the microseismic transient recorders and re-arm the system. A tape-archiving option allows tape storage to take place once the disk has been filled. Display of acquired data is required during setup of data acquisition parameters such as digitizing rate or conditioning gains. The program allows immediate plotting of acquired events, with options for plotting a subset of channels or modifying the vertical and horizontal scaling. Figure 5 shows an example plot of a microseismic event as displayed during data acquisition. DATA ANALYSIS SOFTWARE The data analysis software has been designed to take advantage of the interactive graphics and graphics acceleration capabilities of the workstation. A large part of analysis time involves interactive picks of arrival time and first-motion polarities from displayed waveforms. Ease of use of plotting programs and picking software is one of the features of the analysis programs developed in-house. An extensive description of the acquisition character : istics for each waveform is stored as a header record com- posed of C-language structures. Various pieces of in- formation stored in the header are required for different aspects of the analysis program, such as event plotting, event location, and signal processing. The header record serves as both a convenient stand-alone record of informa- tion about the station and/or event and as an organized means of storing plotting parameters or processing in- formation about each waveform. The hardware graphics engine (boards separate from the computer processor unit (CPU) that accelerate graph- ics instruction to the monitor) is used for display of micro- seismic event locations and mechanisms in time and space. These displays also incorporate geology and/or mine struc- ture for cross-reference (fig. 6) 4 . 3 The authors acknowledge the contribution of Robert Rozen, software engineer, of Vanguard Technologies, Denver, CO, who wrote the original version of the data acquisition and display code, under contract to the Bureau. 4 The authors acknowledge the contribution of Louis Estey, Geophysicist, Ground Control Division, U.S. Bureau of Mines, who wrote the three-dimensional mine structure display software. DATA ACQUISITION PROGRAM FLOW SETUP CAMAC SETUP (DIGITIZING RATE, NUMBER OF CHANNELS,...) PROGRAM PARAMETER SETUP 1.) HARD DISK SPACE, TAPE SPACE 2.) HEADER PARAMETERS 3.) ACQUISITION AND STORAGE MODE BACKGROUND ACQUISITION EVENTS BACKGROUND ON INTERRUPT FROM CAMAC: 1.) TRANSFER DATA 2.) WRITE DISK FILE 3) CHECK DISK SPACE I FOREGROUND AVAILABLE FOR PLOTTING OR ANALYSIS... FOREGROUND ACQUISITION EVENTS FOREGROUND ON INTERRUPT FROM CAMAC: 1.) TRANSFER DATA, DEMULTIPLEX 2.) PLOT ON DISK FULL: 1 .) SUSPEND INTERRUPT SERVICING 2.) WRITE TAPE 3.) RETURN TO PREVIOUS ACQUISITION ON TAPES FULL 1.) FILL DISK 2.) SUSPEND INTERRUPT SERVICING — ^0*0 3.) OPTION TO SAVE DATA TO DISK FILE 4.) CHECK DISK SPACE Figure 4.-Process flow diagram for data acquisition software. o o d> CO in w r^ 0) *» © E a H a o a. r-~ *■» o CL Mb o o o c % o *3 s IS 8 "8 cs en $ > ■•p o ca o o js s c o M CD O 3 C O lO E •§ $ 8 c o > "tf o o E o 0) a 8 o o E 8 o m >• ro a "O 8 3 c o E ^ m o o Q. E a 2 in o •> 3 a> -*- ID o 3 5 o o> o 1 W ■o c m £ 3 1 E a o E M 8 2 u I c i a a is I i SUMMARY A computer workstation has been described with system is flexible by virtue of the CAMAC modularity and associated data acquisition and analysis hardware, which expendability. The multitasking, multiuser computer work- has been configured and used for acoustic emission and station serves the needs for simultaneous data acquisition microseismic waveform recording. The data acquisition and analysis, or for multiple analysis tasks. REFERENCES 1. Brady, B. T. Prediction of Failures in Mines-An Overview. 4. IEEE-488. Digital Interface for Programmable Instrumentation. BuMines RI 8285, 1978, 16 pp. ANSI/IEEE Standard 488, 1978, 83 pp. 2. Cleary, Robert T. The IEEE-583 Bus CAMAC, A Versatile 5. Sondergeld, C. H. Effective Noise Discriminator for Use in Interface Standard, TN-103. Kinetic Systems Corp., Lockport, IL, 1986, Acoustic Emission Studies. Rev. Sci. Instrum., v. 51, 1980, pp. 1342- 12 pp. 1344. 3. IEEE-583. Modular Instrumentation and Digital Interface System (CAMAC). ANSI/IEEE Standard 583, 1982, 81 pp. INT.BU.OF MINES,PGH.,PA 29200 Q 33 > 1 CD I CO CD C 5 CO M D- 5 « b. z O 3 £ o ro j *+ Ss 3" (0 J* CO "^ 3 ** <£> (D 00 ^ o 5' o ^ m D c > r - O "0 -u O 33 H C Z m O -< m DP - ^ u \ -SMS* ^°* \ a* ^.^ o\a^ 01-. <*,*> *&Wg&*\ *++<$ *>. * e „ o » <$ ^^ 7 v*- t v ; ~v 7 ^° # -y % v » • ^ a* .!h t ^ W: V^ /afe: \/ .-aft: V^- -iflte: \/ »»':%/ /^V /... v* 7 ^ bV ^0^ V-^T-\^ %^- T ^o ; ^*^^\# P °o. A ^-»\o° V^\** ^*^-'% < * 4. v °C«. < •y, vvv* .A .♦ ^V"-? ** v \ . \/ :&*, X/ :Mk. \f A' ^' :'A X/ :>Mk\ XS \ ^ ^ •later- ^ ** - ' ** £> •* ^^-°\^^o;%""^ , *° HECKMAN BINDERY INC. |s # FEB 91 N. MANCHESTER, INDIANA 46962 77i* A ,0' U£WV OF C0NG RESS 35S3$? -■' *. : h : ,.v'.''' HUH 11111111 ess •SillifS ggs I .. ■'. ■:.;:■--;;/;;:/; | .; fflffi fill fill §1111 SaP ■Hup * 1 $!,-<, X %f>5|