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英文原文Remnant Roof Coal Thickness Measurement withPassive Gamma Ray Instruments in Coal MinesStephen L. Bessinger and Michael G. NelsonAbstruct:Current underground mining practice often requires that a predetermined amount of coal be left on the roof of the mined-out area. The need to leave such coal occurs on both continuous miner and longwall sections is derived from considerations of ground control, quality control, machine guidance,or simply good operating practice. Efforts at measuring boundary coal thickness have been employed mechanical, nucleonic, and energy adsorption and reflection methods. The nucleonic methods have found application in operations in the United Kingdom,the United States, the former Soviet Union, and Poland. Natural gamma devices are currently the instrument of choice, and several successful installations exist. The calibration of natural gamma background (NGB) instruments must be carefully maintained,and they cannot be used in areas where a NGB radiation is not present. This radiation is ordinarily present in the fine-grained sedimentary rocks that bound many coal seams.I. INTRODUCTIONModern underground coal mining practice often includes leaving coal on the roof of the mine after mining is completed. Roof coal is often left on continuous miner sections for ground control purposes to prevent the failure of an immediate roof that consists of weak, friable rock. Roof coal may also be left in mines where concentrations of sulfur or ash are higher near the top of the seam to reduce the concentrations of these impurities in the salable product. Control of coal quality in this manner is especially advantageous in mines with longwall sections, where a large fraction of the production originates from one general area of the seam, making blending for quality control more difficult.Small amounts of roof coal may also be left for purposes of machine guidance. This practice is common in applications where the coal-cutting machine is to be in an automatic control mode. Longwall face operation in this manner has been demonstrated in the United Kingdom 1, 2, and similar systems have been tested in the United States 3, 4. Leaving a measured amount of roof coal in such applications makes it possible to guide the shearing machine, keeping it in the seam.Leaving both roof and floor coal can enhance both the performance and reliability of the cutting machine by reducing its exposure to the high mechanical stress that is experienced when cutting the rock bordering the seam. This can increase pick life and reduce the wear on all parts of the cutting system 2, 5.The need to leave roof coal leads directly to the need for measurement of the thickness of the coal layer left on the roof. Many methods for making this measurement have been investigated. Manual methods, including drilling and borehole inspection, are time consuming and often unreliable.Many instrumental methods have been investigated, including vibration analysis, pick force sensing, ultrasonic and radar detection, and nucleonic methods, but only the nucleonic methods have been used in actual production. The research conducted by CONSOL Inc. on nucleonic methods will be described in this paper. GAMMA-RAY BACKSCATTER SENSINGThe use of gamma-ray backscatter sensing for machine guidance was suggested as early as 1958 6. An active nucleonic device for coal thickness measurement was proposed in Great Britain in 1961 7 and designed in 1973 8, 9. In this device, a source of gamma radiation (usually cesium 137 or americium 247) is enclosed in a housing that is positioned near the surface to be measured. The gamma rays interact with the coal and rock, and are subject to both Compton scattering and attenuation. The backscattered rays are measured by a gamma detector, and coal thickness is calculated from a calibration curve.Several designs of this type of sensor were tested in England, and a commercial model manufactured by Dowty was tested by CONSOL in West Virginia. A prototype was also tested by NASA in the USBM test mine in Bruceton, PA. In every instance, several problems were encountered. Most significant was the variable effect of the air gap between the sensor and the coal surface. Because of this effect, sensors were designed to operate in contact with the surface, which presented severe difficulties in actual mining operations. In addition, with the low-energy gamma radiation employed, coal thicknesses greater than 200-250 mm (8-10 in) could not be measured. It was also found that any variation of materials in the boundary coal or the immediate roof could significantly but unpredictably alter the calibration. Finally, the presence of an active radiation source in a typical underground mining environment raised concerns of safety and source control. Because of these problems, gamma backscatter sensors have been generally abandoned in favor of other devices11. NATURAL GAMMA BACKGROUND SENSINGDuring the testing of various gamma backscatter sensors, it was observed that in many coal seams, the neighboring rock emits a “natural” gamma radiation 12. It has been shown that this gamma background results from the presence of traces of various radioactive isotopes in the rock. The background is generally high in shale, lower in sandstone, almost absent in limestone, and virtually undetectable in coal. Radiation from the roof rock is attenuated by any coal left in place, according to the well-known exponential attenuation equation 13:Where attenuated intensity in counts per second source intensity in counts per second attenuation coefficient in reciprocal centimeters thickness of attenuating material in centimeters.Intensity I is measured by counting gamma ray emissions in a given time, and coal thickness may be determined from the attenuation equation using an empirically derived attenuation coefficient and known background radiation Io.Although the gamma background varies with the composition of the bordering strata, it is often very consistent over wide areas in a given mine or even a given seam. The attenuation coefficient of coal is also reasonably constant because carbon is by far its major constituent. The gamma background is essentially a planar source, and since the attenuation due to air is much less than that due to coal, the distance from the sensor to the roof is not critical. In most instances, coal thicknesses up to 500 mm (20 in) can be measured.Where the strata bordering the seam has a NGB, the passive gamma sensor provides all the advantages of the active gamma device with none of the associated problems. For these reasons, NGB sensors have become the device of choice, particularly in Great Britain 2. They have also been tested successfully in the United States in many locations such as in the Pittsburgh seam in both Pennsylvania and West Virginia and various seams in Kentucky, Illinois, Wyoming, and New Mexico 10, 14. A typical attenuation curve, which was measured in the Pittsburgh seam, is shown in Fig. 1.Fig. 1. Exponential attenuation curve shown for NGB-1000 instrument.Three significant difficulties may arise with the use of a NGB sensor. First, the strata bordering the coal seam may not have a gamma background, or the background may be too low to facilitate meaningful measurements 15. This condition may be minewide (for example, in a mine with a massive sandstone roof) or may occur sporadically (from sand channels, “false roofs,” or similar conditions). In the first instance, the sensor is simply unusable; in the second, it must be used judiciously with frequent checks of both calibration and accuracy.The second difficulty that may be encountered is an intrinsic variation in the gamma background that does not result from secondary disturbances. Occurrence of this condition is entirely site specific and may be determined only by field measurement. It is also accomodated by frequent checks of the instruments calibration and accuracy. An understanding of the depositional geology of the roof rocks can be useful in assessing the probability of this type of variation.The third difficulty that must always be dealt with arises in the process of deriving information from radiological count data. Because radioactive emission is a random process, the accuracy of information derived from count data is directly related to the number of counts recorded 16. This means that a very accurate coal thickness measurement requires either a very large detector or a very long counting time so that in either case, a large number of counts may be recorded 11. INSTRUMENT TESTINGA variety of gamma detectors were evaluated in both laboratory and underground tests. Two hundred test holes were drilled in the roof of a Pittsburgh seam mine (here known as Mine One). The roof-coal thickness at each hole was determined as accurately as possible, first by observing drill cuttings and then by borescope and fiberscope inspection. After a given detector configuration was found to work satisfactorily in the laboratory, it was tested at the underground site by recording multiple instrument readings at each test hole and comparing these with the known coal thickness at that point.Fig. 2. Correlation of thickness readings.An instrument that had a consistent accuracy of 25 mm was tested underground in 1984. This instrument comprised a cluster of seven gamma detectors, where each was a 25-mm- diameter 50-mm-thick sodium iodide scintillator coupled to a photmultiplier tube. Readings were taken by averaging the counts measured by each detector in a 1-min time period. The detector cluster was shielded by 3.8 mm of lead to omit gamma counts originating from the floor and rib (walls). Final tests of the clustered-detector instrument were conducted in Mine One in 1984 to determine its accuracy when operating on a moving machine. At speeds of 2.5 to 3.0 m/min, the accuracy was still 25 mm. A developmental NGB instrument (the NGB-1000) was also tested in 1984. The NGB-1000 coal thickness sensor (a NASA-designed device) is comprised of a sensing head with a single scintillation crystal (51 102 204 mm) a photomultiplier tube, and a control panel. The control panel provides counts-to-thickness conversion, selectable sampling time (5 to 20 s), and digital thickness display. The sensor is large (228 228 610 mm) and, because of the required shielding, weighs almost 90 kg. The instrument is now permanently approved by the Mine Safety Health Administration (MSHA) for use in underground coal mines.Tests at the Mine One test site showed that the accuracy of the NGB-1000 using a 20-s sampling time was comparable with that of the clustered-detector instrument using a 60-s sample time. Fig. 2 shows correlation plots for the readings of the NGB-1000 with the roof coal thickness at each site as estimated by observation with a borescope. Because of this superior performance, it was decided that the NGB-1000 was the preferable instrument for machine installation at another mine (here known as Mine Two).V. OPERATING INSTALLATIONThe NGB-1000 was installed on a continuous miner in Mine Two. This West Virginia Mine is also in the Pittsburgh seam, and its gamma background levels were found to be almost identical to those of the first mine. Conditions at Mine Two require that 100 to 150 mm (4-6 in) of coal be left at the roof boundary of continuous miner development sections. This roof coal is required because the shale in the immediate roof is friable and weak. In the past, operators have used a rock band that is usually visible near the top of the seam as a guide in maintaining the proper cutting horizon. However, this is not always reliable. Earlier observation showed that the actual thickness of the coal left on the roof varied widely; further, it was noted that occasional, accidental excursions into the immediate roof required supplementary roof control measures such as installation of planks or center bolts. Thus, it was concluded that operators needed a better source of guidance for control of the cutting horizon, and a roof coal thickness sensor was scheduled for installation. The NGB-1000 sensor was installed on a Joy 12CM10 continuous miner in June of 1988. The sensing head was mounted on the cutter boom of the miner, and the control panel was mounted in the operators cab. Power for the sensor was initially derived from an intrinsically safe battery power supply. This worked well for a few weeks, but eventually some battery power supplies were discharged too deeply to allow recharging. Consequently, a request was filed with MSHA to allow the sensor to be powered through intrinsic safety barriers by an electronic power supply connected to machine power. The permit was granted, and the sensor was connected to machine power.After the sensor was connected to machine power, the only operating problem experienced was the occasional failure of cables. A supply of the required cables was made and delivered to the mine so that damaged cables could be quickly replaced. Much of the cable damage that was experienced could be eliminated by slight modifications to the miner during a rebuild, allowing cables to be installed in more protected locations.After the sensor had been in operation for approximately two months, a survey was made to determine its effect on mining operations. A hand-held gamma detector was used to measure roof-coal thickness in 35 locations along the track in the mining development section. The measured coal thicknesses from the survey are plotted in Fig. 3. The point at which the NBG-1000 was installed (block 51) shows clearly, as does the period in which the battery power supplies were not working, blocks 52 and 53. A further indication of the improvement brought about by installation of the NGB-1000 appears in Fig. 4, which shows the population variance among groups of three roof-coal thicknesses, as measured in the survey. Clearly, use of the sensor improves the consistency with which the roof horizon is cut.Fig. 3. Measured coal thicknessIn addition to the improvement in as-mined, roof-coal thickness control, another improvement was also observed. In the first 57 blocks of the track entry, it was noted that the miner had cut into the immediate roof 27 times, requiring corrective action. In 13 instances, center bolting was required; in the remaining 14, planks were installed without center bolting. In the next 14 blocks, which comprised the survey area, only one incident of cutting into the roof was observed.In severe roof-cut incidents, where large areas of immediate roof rock are exposed, additional costs may be generated when more extensive remedial roof control measures are required and when large falls occur that require cleanup, which results in lost production.VI. DISCUSSIONThe NGB-1000 was readily adopted by mine operators as a useful aid to good mining practice. The use of a coal thickness sensor can also result in significant cost savings in a situation such as that described above. Economic benefits derived from the use of a coal thickness sensor result from four factors:1) Higher resource recovery resulting from closer control of the amount of roof coal left after mining2) lower auxiliary roof control costs resulting from reduced incidence of cutting into the roof rock3) higher productivity resulting from reduced time spent in auxiliary roof control4) higher productivity resulting from a reduced level of operator uncertainty during cutting of the roof.Fig. 4. Roof coal thickness varianceIn consultation with mine management personnel, estimates of cost savings derived from these factors were made. Using those estimates, the net present value for a coal thickness sensor and its installation on a continuous miner was calculated by standard methods. Those calculations showed clearly that the installation of the sensor was economically advantageous; the pay-out period was less than one year.REFERENCES1 D. Law, “Auto-steerage-An aid to production: Part one,” Mining Eng.vol. 148, no. 328, pp. 326-335, 1988.2 Anon, Coal Face Automation. Burton-on-Trent: National Coal Board,Mining Res. Development Est., 1984, p. 6.3 T. J. Fisher and E. R. Palowitch, “Overview of the Department of Energys program on the development of automated machinery for underground mining,” Proc. Fourth Con$ Coal Mine Electrotechnol. (Morgantown, WV), Aug. 2-4 , 1978, pp. 33-11-33-15.4 R. E. Pease, “AMEs Longwall automation program,” unpublished paper presented at Longwall USA, June 19-22, 1989, Pittsburgh, PA5 A. E. Bennett, “Automatic steering of shearers,” Mining Technol., vol. 55, no. 631, pp. 181-188, 1973.6 V. G. Segallin and A. A. Rudanovsky, “Stabilization of motion in sinking and extracting machinery with the help of radioactive methods,” Afomnaya Energiya p. 88, Jan. 1958.7 B. J. Greenland, “Radioactive isotope monitoring-Principle and use in steering coal-getting machines,” Colliery Guardian, vol. 209, no. 12, pp. 684-688, 1961.8 P. A. Wood, “Remote and automatic control of Longwall mining,” IEA Rep. ICTIS/TR19, IEA Coal Res., London, June 1982, p. 58.9 V. M. Thomas, “Case study: The development of an instrument to measure coal seam thickness,” in Measurement for Instrumentation and Control (M. G. Mylroi and G. Calvert, Eds.). London, Peter Peregrinus, 1984, pp. 251-279.10 P. Broussard and W. B. Schmidt, “The Longwall automation research project of the U.S. Department of Energy,” Mining Technol., vol. 64, no. 726, pp. 138-143, 1981.11 J. S. Wykes, I. Adsley, L. R. Cooper, and G. M. Croke, “Natural gamma radiation: A steering guide in coal seams,” In?. J. Applied Radiation Isotopes, vol. 34, no. 1, pp. 23-26, 1983.12 Anon, “Coal thickness indicator keeps face machine on current horizon,” Mining J., vol. 294, no. 7656, p. 505, 1980.13 W. H. Tait, Radiation Defecrion. London: Buttenvorths, 1980.14 M. J. Pazuchanics and E. R. Palowitch, “Coal interface sensors for automated mining machines,” in Proc. Fourth Con$ Coal Mine Electrotechnol. (Morgantown, WV), Aug. 2-4, 1978, pp. 33-1-33-1 t.15 D. Hunter, “Computerized shearing aids output,” Coal Age, vol. 62, no. 8, pp.64-68 , 1983.16 G. y. Knoll, Radiation Defection and Measurements. New York, 1979.Author introductionStephen L. Bessinger received the B.S. and M.S.degrees in mining engineering from the Colorado School of Mines. He is also a doctoral degree candidate at West Virginia University in the College of Mineral and Energy Resources.He holds Professional Engineering Registration and various mining supervisory certifications. He is a Senior Research Engineer at the Consol Inc.Research and Development Department. He is responsible for advanced technology longwall mining activities within the Department.Michael G. Nelson received the B.S. degree in metallurgical engineering and an M.S. degree in applied physics, both from the University of Utah.He received the Ph.D. degree in mineral engineering from West Virginia University.He has worked extensively in the application of modem techniques of instrumentation and control in the minerals industries, and has been granted seven patents covering his work in control of coal processing plants, instrumentation, and mining machine automation. His current research interests include the physical and economic modeling of precious metals recovery systems and the reclamation of tailings from placer mines and cyanide leach operations in the Far North. He is currently associate professor of mining engineering in the School of Mineral Engineering at the University of Alaska in Fairbanks.He has 18 years of experience in the minerals industries, including work in copper smelting, steelmaking, zirconium production, Coal mining, and gold recovery. He is president of Alaska Mining Services, in which capacity he has acted as a consultant to several industrial clients.Dr. Nelson is a member of the Society for Mining, Metallurgy, and Exploration and a senior member of the Instrumentation Society of America.He also serves on the board of directors of the Alaska Miners Association.中文译文伽马射线传感仪在煤矿残顶煤厚度测量中的应用Stephen L. Bessinger and Michael G. Nelson摘要：当前，地下煤层开采时，经常需要在采空区留预定数量的煤对顶板进行支撑。有必要在连续采煤机和长壁工作面之间留下这些煤是来源于对于地面控制，质量控制，机器指导，或是简单良好的实践经验的考虑。测量边界煤层厚度方法的突破一直局限在机械、终止的核子、能源的吸附和反射的方法上。在英国、美国、前苏联和波兰，核子的方法被发现应用在手术中。自然伽玛辐射传感仪是目前的首选工具，并多次成功安装使用。自然伽马辐射（NGB）的校准仪器必须精心维护，而且他们不能在一个不存在NGB辐射的领域使用。这种辐射通常存在于以细粒沉积岩为顶底板的煤层中。I 前言现代地下煤炭开采往往留一部分煤对矿井顶板进行支护当矿井煤炭开采完成后。顶煤往往留在连续采煤机的上部，是为了得到地面控制的目的，去阻碍由弱、易碎的岩石组成的直接顶垮落。在矿井岩孔、岩隙有较高浓度的硫和灰分时，顶煤也可能被留下，目的是去减少这些采出的煤中的杂质。以这种方式对煤炭质量进行控制在长壁采煤法中是非常有利的，特别是在有一大部分煤都是从裂隙、孔隙较发育的岩层附近采出时，这些煤炭和其他煤炭混合后，煤炭质量的控制就变得更加困难。少量的顶煤也可以被留下来作为机器的导向。这种做法经常应用于采煤机的自动控制模式。综采工作面作业以这种方式已在英国证明1，2，以及类似的系统已经在美国3，4测试。在这种情况下，留有一定数量的顶煤作为采煤机的导向，使采煤机在轨道上行驶成为可能。当切割节理裂隙发育的岩层时，留下顶煤和底煤可以提高采煤机的性能和可靠性，主要是通过减少采煤机暴露在高的机械应力下。这样可以增加采煤机滚筒截割头的寿命，同时减少截割部其他部位的磨损2，5。留下顶煤的必要性直接导致需要测量留在顶板煤层的厚度。针对这种测量的许多方法已经被调查过。手动的方法，包括钻井和井眼检查，耗时长而且往往不可靠。对许多仪器分析方法也进行了研究，包括振动分析，选择力传感，超声波，雷达探测，和核子方法，但只有核子方法已在实际生产中使用。由康寿公司进行核子方法的研究将在本文介绍。 伽玛射线散射传感早在1958年6，伽玛射线散射传感就被建议作为机器向导使用。1961年在英国7，测量煤层厚度的一个活跃的终止的核子装置被提出，并在1973年8，9被设计出来。在此元件中，伽玛射线（通常是铯137或247）的一个来源被围在一个住房，这个住房定位在地表附近被测量。伽玛射线与煤岩相互作用，而且会发生康普顿散射和衰减。伽玛射线散射后由一个伽玛探测器进行测量，煤层厚度从一个校准曲线上计算得出。在英国，对这种类型传感器的几种设计进行了测试，接着道蒂公司制造了一个商业模型，这个模型被西弗吉尼亚州的康寿公司进行了测试。在布鲁斯顿的美国矿业局，美国航空航天局对测试矿的一个原型也进行了测试。在每种情况下都遭遇了几个问题。最重要的是发现传感器和煤的表面之间的气隙变量影响。因为这个发现，传感器被设计去操作接触煤的表面，在实际采矿作业中，这件事被认为是非常困难的。此外，随着低能伽马射线的使用，煤层厚度大于200-250 mm（8-10英寸）时，不能被测量。同时也发现，边界煤或者直接顶任何材料的改变，可以观察到，但是不能预测它的改变，并进行校准。最后，在一个典型的地下开采环境中发现存在一个活跃的辐射源，它提高了安全的顾虑和对源码的控制。因为这些原因，伽玛散射传感器已经普遍放弃在其他设备中应用11。 自然伽马辐射传感在各种伽马散射传感器的试验过程中，观察到在许多煤层相邻岩石散发出一种“天然”的伽马射线12。有证据表明，这种伽马辐射导致在岩石里发现各种放射性同位素的痕迹。通常，这种辐射在页岩中很高，在砂岩中较低，在石灰石中几乎没有，在煤中几乎无法察觉到。顶板岩石是通过留下的煤进行辐射，根据指数衰减方程13：式中：衰减强度的计算，s；源强度的计算，s；衰减系数，cm；衰减材料厚度，cm。衰减强度I0是在一个给定的时间内通过计数伽马射线的排放次数进行测定的，衰减方程通过一个实证研究，可以推导出衰减系数和已知的伽马辐射I0，同时煤层厚度也可能被确定。尽管伽马辐射是随着周边地层组成的不同而变化的，但是在一个给定的矿井，甚至一个给定的煤层，它一般还是非常一致的。对煤的衰减系数也相当稳定，因为迄今为止，二氧化碳是它的主要组成部分。伽马辐射实质上是一种平面的源头，它在空气中衰减和在煤中衰减相比较非常小，所以测得从传感器到顶板的距离并不准确。在多数情况下，煤厚度达500 mm（20英寸）可以被测量。煤层上覆岩层接壤的地方有一个自然伽马辐射,被动伽马传感器提供了主动伽玛装置所具有的所有优势，并且还没有主动伽玛装置所具有的相关问题。由于这些原因，自然伽马辐射传感器已经成为首选设备，特别是在英国2。在美国在许多的地点，他们也曾经进行了成功的测试，如在宾西法尼亚州和西维吉尼亚的匹兹堡缝中，以及在肯塔基，伊利诺斯州、怀俄明州、和新墨西哥州的各种缝中10，14。一个典型的衰减曲线，它是衡量在匹兹堡的孔隙，如图1所示。图1 指数衰减曲线显示的NGB-1000仪器随着自然伽马辐射传感器的使用，出现了三个重大困难。第一，地层接壤的煤层也许没有一个伽马辐射，或者是伽马辐射太低以至于不便于进行有意义的测量15。这种情况可能很常见（例如，在有一个巨大的砂岩顶板的煤矿。），或者也可能很少见（伽马辐射来至于泥沙，“伪顶”或者相似的条件）。首先，传感器是无法很容易使用的；第二，必须通过频繁的校准传感器来确保其准确性，才能慎重地使用它。第二种可能遇到的困难是伽马辐射中的一种内在变化不是来至于次要干扰。发生这种情况是取决于整个站点具体的条件，也许只取决于通过现场实测。同时也包括经常校准仪器以保证其准确性。沉积地质学中对顶板岩石的理解在评估这种类型变异的可能性中可能会有用。第三个难题是必须始终处理在这一过程中产生的放射性计数的推导信息数据。因为核辐射是一种随机过程，从统计数据中推导出的信息的准确性与纪录数据的数量直接相关16。这意味着，一个非常精确的煤层厚度的测量，不仅需要一个非常大的探测器，而且需要很长的计算时间，以至于在这两种情况下，大量的数据才可能被纪录11。 仪器测试各种各样的伽玛探测器在实验室进行了评估和地下核试验。两百年的测试孔在匹兹堡煤层矿井顶板上钻（这里被称为一个矿山）。在每个孔的顶煤厚度都被尽可能准确地确定，首先通过观察钻屑，然后通过内窥镜在纤维内检查。一个给定的探测器配置后，发现在实验室工作令人满意，它在地下被测试，通过记录每个测试孔的多仪器读数，然后拿这些数据和已知厚度的煤层在同一点上比较。图2 相关的厚度读数在1984年，对精确度为 25的一种仪器在地下进行了试验。该仪器由七个伽马探测器组成，每个探测器都由直径为25 mm，厚度为50 mm的碘化物闪烁器耦合到一个光电倍增器管上形成。数据是通过每个探测器在一分钟内的平均计数测量取得的。该探测器群被3.8 mm的铅屏蔽，导致伽马计数器在底板和两帮中获得的数据减少了。1984年，群探测器的最终测试在一个矿井的移动机器上操作以确定其准确度。当速度为2.53.0 m/min，准确度仍然为25mm。控制面板提供计数厚度转换，可选择的采样时间（5至20 s）和数字显示厚度。由于需要屏蔽，该传感器比较大（228 228 610 mm），重90 kg。目前，该仪器是由矿山安全健康管理局（MSHA）永久批准使用的，用于煤矿井下使用。该矿一个现场的测试表明，该NGB-1000使用20 s采样时间所测的数据的精确度可以与聚集探测器使用60 s采样时间测得的数据的准确性相比，图2表示NGB-1000通过内窥镜观察估计出每个站点的顶煤厚度的读数。由于这种优越的性能，它是决定NGB-1000在另一个矿井作为安装的机器中的最好工具（这里被称为二矿）。 安装操作系统在二矿，NGB-1000是安装在一个连续采煤机上。这个西弗吉尼亚州煤矿也是在匹兹堡缝，它的伽马辐射水平被认为与第一个矿山几乎是相同的。二矿需要在连续采煤机滚筒上部的顶煤边界留下100150 mm（46英寸）厚度的煤。因为直接顶岩层的易碎和不稳定性，这些顶煤是需要留下来的。在过去，操作者已经用过煤层顶部的可见岩石帮作为适当切割低煤的一个导向。但是，这并不总是可靠的。早期的研究表明，实际留下的顶煤的厚度是差别很大的，更进一步的，也有人指出采煤机滚筒可能偶尔的割到直接顶，这就需要制定顶板控制措施，例如安装木板和中心螺栓。因此，可以得出结论，操作者需要一个良好的指导来源去控制把顶煤割平整，所以一个煤层厚度传感器就应运而生了。1988年6月，NGB-1000传感器被安装在一个型号为12CM10的连续采煤机上。传感头安装在采煤机滚筒上，控制面板安装在司机室。该传感器的电源最初由一个本质安全的电池进行供电。前几个星期，这些电池运作良好，但是最终一些电池的电量供应太低以至于不能再次进行充电。最后，请求被提交的MSHA通过一个电子电源连接到采煤机电源上，使得传感器可以在本质安全电池上进行充电。把传感器直接连到采煤机的电源上也是可以的。图3 煤层厚度的测量在传感器直接连到采煤机的电源后，后来运行过程中出现的唯一的问题就是偶尔电缆出现故障。大量所需要的电缆被制造，然后运送到矿井，以便可以及时更换受损的电缆。煤矿在维修时，经验丰富的矿工对受损的电缆进行稍作修改就可以消除损害，允许电缆在多个受保护的地点安装。在传感器运作了大概两个月后，作出了一项调查，以确定其对采矿业的影响。在沿着煤炭发育的地方布置35个测量点，用手持伽马射线探测器测量顶板煤层的厚度。调查中所测得的煤层厚度数据绘制成图3。安装NBG-1000的点（第51组）测得的数据很清楚，尽管那段时间电池不能充电，第52和53组。进一步表明了改进的NGB-1000所测得的数据绘制成图4，从图4可以看出，在调查中所测得的三组煤层顶板厚度的数据变化很小。显然，使用传感器后煤层被切成平整的可能性被提高了。煤炭开采中除了需要提高对顶板煤层厚度的控制，同时也需要提高对顶板煤层的观察程度。在轨道平巷中测得的前57组数据中，表明矿工曾27次让采煤机割到直接顶，需要采取纠正措施。在13个情况下，中心螺栓是必须的；在剩下的14个情况下，没有中心螺栓，木板被安装。在接下来的14组数据中，其中包括调查区域，被观察到采煤机只有一次意外的割到直接顶。在严重的切顶事故中，其中大面积的直接顶暴露，当采取更广泛的直接顶控制措施时，可能会产生额外费用，当大面积直接顶冒落时，将导致生产的损失。图4 顶煤厚度变化 结论在采矿实践中，NGB-1000是一个很有用的工具，很容易被煤矿经营者接受使用。一个煤层厚度传感器的使用也可能导致一种情况，大大节省成本，如上面述。使用煤层传感器的经济效益表现为四个因素：1）更高的资源回收造成更严格的控制开采过程中留下的顶煤量；2）较低的辅助顶板控制产生的费用导致意外割进顶板岩层次数的减少；3）更高的生产率导致减少了在辅助顶板控制过程中所花费的时间；4）更高的生产率导致在割顶煤过程中一个水平较低的操作者的不确定性。估计是由于这些因素，导致矿山管理人员节省了费用。利用这些估计，通过标准方法计算一个煤层厚度传感器及其安装在连续采煤机上的净现值。那些计算结果清楚地显示安装的传感器在经济上是有利的，投资回收期用不了一年。参考文献1 D. Law,