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FACTORS GUIDING SYSTEM DESIGN <br />Besides low cost, reliability, and flexibility were important considerations in system design. The <br />expense and downtime associated with timely repair and/or replacement of custom data <br />acquisition and processing hardware, as experienced with some previous USBM systems, was [o <br />be avoided. Mass-produced personal computers (PC's) and commercial multichannel analog-to- <br />digi[al (A/D) converters minimize capital expenditures and repair costs and provide a high degree <br />of reliability. <br />Other factors influencing this design effort were distributed processing, automation, lowcos[ <br />installation, and availability of software. <br />A distributed network of data collection computers (Figure 1) was selected rather than a single <br />centralized system for several reasons. <br />(I) A distributed system avoids single-point failures that result in complete loss of monitoring <br />coverage. <br />(2) Networking several small-scale autonomous seismic networks [hat share data avoids [he <br />installation of an expensive and difficult [o maintain network of long cables. <br />(3) In many, if not most, mining situations, it is extremely difficult to completely surround the <br />area of interest with sensors from accessible underground workings alone. Encircling the area of <br />interest with sensors is a basic requirement for locating seismic events accurately. Drilling <br />boreholes for sensor installation is an expensive and difficult option not generally available to <br />relatively short-term NIOSH research studies and is not practical for high-production mining <br />environments that rapidly sweep through large areas. The use of several smaller autonomous <br />arrays distributed on the surface, underground, in surface boreholes, in neighboring mines, on <br />different underground levels, etc., can surround the area of interest and help provide the needed <br />three-dimensional coverage. <br />(4) Delivery of summary processed results to mine personnel stationed underground and on the <br />surface was an additional constraint satisfied by a distributed data acquisition and processing <br />scheme. <br />Processor-n <br />Processor-1 <br />Figure 1. PC-network-based seismic acquisition and <br />processing system. <br />