1.1 目的和应用 — 本指南总结了使用金属检测方法评估地下材料的设备、现场程序和解释方法。金属探测器通过在导电物体中感应涡流来响应黑色金属和有色金属的存在。金属探测器是频域（连续频率或波）或时域（脉冲）系统。广泛的金属探测器通常可用。 1.1.1金属探测器可以检测任何类型的金属材料，包括铁和钢等黑色金属以及铝和铜等有色金属。 相比之下，磁强计只能检测黑色金属。 1.1.2金属探测器测量可用于检测埋地金属垃圾桶的存在（Tyagi等人，1983年） (1) 和储罐、废弃井（指南 D6285 ); 追踪埋地公用设施；并划定填埋金属和沟槽金属的边界。它们还用于探测金属基未爆弹药。 1.2 局限性 : 1.2.1本指南概述了金属检测方法。本指南不提供或说明理论、现场程序或数据解释的细节。为此目的包括参考文献，并被视为本指南的重要组成部分。 建议本指南的用户熟悉引用的参考文献和ASTM标准 D420 , D653 , D5088 , D5608 , D5730 , D5753 , D6235 , D6429 和 D6431 . 1.2.2本指南仅限于在陆地上进行的金属检测测量。金属检测方法可适用于陆地、水上、空中和冰上的许多特殊用途。 1.2.3本指南中建议的金属检测方法是普遍使用、广泛接受和经验证的方法。然而，可以替代技术上合理的金属检测方法的其他方法或修改。 1.2.4 本指南提供了有组织的信息收集或一系列选项，并不推荐具体的行动方案。 本文件不能取代教育或经验，应与专业判断一起使用。并非本指南的所有方面都适用于所有情况。本ASTM标准不代表或取代必须根据其判断给定专业服务的充分性的谨慎标准，也不应在不考虑项目的情况下应用本文件 ’ 它有许多独特的方面。文字 “ 标准 ” 在本文件标题中，仅表示该文件已通过ASTM共识程序获得批准。 1.3以国际单位制表示的数值视为标准值。括号中给出的值为英寸- 磅单位，仅供参考，不被视为标准单位。 1.4 注意事项 : 1.4.1 本指南的用户有责任遵循设备制造商建议中的任何预防措施，并建立适当的健康和安全实践。 1.4.2 如果在有危险材料、操作或设备的现场使用该方法，则本指南的用户有责任在使用前制定适当的安全和健康做法，并确定任何法规的适用性。 1.4.3 本标准并非旨在解决与其使用相关的所有安全问题（如有）。 本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管要求的适用性。 ====意义和用途====== 概念 : 本指南总结了使用金属检测方法定位地下金属物体的设备、现场程序和解释方法。人员要求如实践中所述 D3740 . 方法 — 金属探测器是根据感应原理工作的电磁仪器，通常使用两个线圈（天线）；发射器和接收器。两个线圈相互固定，并在地球表面附近使用。 向发射器线圈施加交流电压或脉冲电压，从而在地球上感应电涡流。在地球上流动的电流与介质的电导率成正比。这些电流在接收器检测和测量的埋地金属物体中产生涡流（图1）。 参数测量值和代表值 : 频域金属探测器 : 频域金属探测器向发射线圈施加具有固定频率和振幅的交流电，从而在线圈周围产生时变磁场。 该磁场在附近的金属物体中感应涡流，进而产生其自身的时变磁场。这些涡流场在接收器线圈中感应电压。金属的存在导致接收器电压的相位和幅度发生微小变化。大多数金属探测器会放大附近金属引起的接收器线圈电压差，并产生声音或仪表（模拟或数字）读数。 地面电导率仪（频域金属探测器）同时测量二次磁场的两个分量。第一个是正交相位分量，表示土壤电导率，测量单位为毫西门子/米（mS/m）。 第二个是同相分量，它与地下磁化率有关，以千分之几（ppt）测量（即一次磁场和二次磁场之间的比值）。 ( 1. ) 电导率测量（正交相位分量） 表面几英尺内的金属物体会引起感应磁场畸变，导致测量电导率为零甚至负值。较深的金属物体将导致较小的场畸变，并导致测量的电导率与现场背景值相比异常高。 ( 2. ) 同相分量 同相测量比电导率测量对金属更敏感。 因此，同相异常可能表明在比电导率测量更大的深度存在金属。 时域金属探测器 : 在时域金属探测器中，发射器在地球上产生脉冲初级磁场。每次脉冲后，中等导电性的地球会短暂地感应二次磁场，而金属目标会在更长的时间内感应二次磁场。在每个脉冲之间，金属探测器等待，直到导电接地的响应消失，然后测量延长的埋置金属响应。该响应的测量单位为毫伏（mV）。 设备 — 金属探测器通常由发射器电子设备和发射器线圈、电源、接收器电子设备和接收器线圈组成。 金属探测器通常是单个便携式的。 典型的 “ 寻宝者 ” 金属探测器在检测到金属时提供音频信号和/或仪表读数（模拟或数字）。 地面电导率仪的正交和同相测量显示在模拟或数字仪表上。这些测量通常可以使用小型现场记录仪、条形图记录仪或计算机在现场进行数字记录。 时域金属探测器可以由一个或两个接收器线圈组成。当使用两个线圈时，通常将一个线圈置于另一个线圈之上。同时记录两个线圈的读数。 为了提高对较深金属目标的检测，可以使用两个接收器线圈的差分响应来抑制较小、较浅金属目标的响应。一些时域金属探测器安装在车轮上，允许使用里程表提供位置数据。 限制和干扰 : 地球物理方法固有的一般局限性 : 所有地球物理方法的一个基本限制是，一组给定的数据不能与一组独特的地下条件相关联。在大多数情况下，仅凭地表地球物理测量无法解决所有歧义，建议提供一些附加信息，如钻孔数据。 由于地球物理方法的固有局限性，仅金属探测器测量永远不能被视为对地下条件的完整评估。金属探测器测量与其他地质信息适当结合，是获取地下信息的高效方法。 此外，所有地表地球物理方法固有地受到分辨率随深度降低的限制。 金属检测方法的特定限制 : 影响金属探测器响应的几个因素:目标的特性、土壤/岩石的特性以及金属探测器本身的特性。 目标 ’ 大小、深度和埋藏条件是三个最重要的因素。 目标的表面积越大，可能感应到的涡流越大，检测目标的深度也越大。 金属探测器 ’ s响应以等于其深度倒数的速率减小，直至六次方（1/深度 6. ). 因此，如果到目标的距离加倍，金属探测器的响应将减少64倍。因此，金属探测器是一种相对较浅的深度装置。它通常仅限于检测相对较浅深度的小目标或有限深度的较大目标。 通常，大多数金属探测器无法对深度远大于6 m的目标做出响应。 虽然目标的形状、方向和成分会影响金属探测器的响应，但这些因素的影响比目标的大小和深度小得多。然而，目标恶化具有重大影响。金属容器在自然土壤条件下会腐蚀。如果容器被腐蚀，其表面积将显著减少，进而会降低金属探测器的响应。 因为金属探测器 ’ 随着与目标距离的增加，s响应迅速减弱，系统增益和仪器稳定性至关重要。 线圈的尺寸控制可检测的金属目标的尺寸和深度，如图2所示。 自然和文化条件造成的干扰 : 此处提及的噪声源不包括物理性质的噪声源，如困难地形或人为障碍物，而是可能对测量和解释产生不利影响的地质、环境或文化性质的噪声源。 自然噪声源 — 某些类型的土壤/岩石，特别是含铁量高的土壤（通常称为矿化土壤）对接收器线圈输出的影响很大，足以表明存在具有某些类型金属探测器的金属目标。 某些类型的金属探测器提供了一种补偿地面效应输出的方法。这通常需要操作员将探测器放置在地面附近（但不靠近金属目标）并调整控制装置，直到目标信号消失。土壤特性和石块（尤其是含有金属化合物的石块）的微小变化可能会导致探测器输出发生微小变化。这些变化通常会导致小的目标信号，称为 “ 接地噪声。 ” 这些可能会让操作员感到困惑，因为它们听起来像小目标。 文化噪声源 — 文化噪声源可能包括来自电力线、通信设备、附近建筑物和金属围栏的干扰。 电源线的干扰与电源线和探测器之间的距离成反比；因此，大多数带有小线圈的金属探测器通常不受影响。 不应在建筑物、金属围栏或可通过金属检测方法检测到的埋地金属管线附近进行测量，除非测量对象是埋地管线。有时很难预测与潜在噪声源的适当距离。现场测量可以快速得出问题的严重程度，然后可以进行调整。 还必须采取预防措施，以清除操作员身上的金属，或将其影响降至最低。 钢趾靴、呼吸器和气瓶都会造成相当大的噪音问题。 总结 — 在设计和执行金属检测调查的过程中，必须考虑环境、地质和文化噪声源，并注明发生时间和位置。干扰的确切形式并不总是可预测的，因为它不仅取决于噪声的类型和噪声的大小，还取决于与噪声源的距离，可能还取决于一天中的时间。

1.1 Purpose and Application — This guide summarizes the equipment, field procedures, and interpretation methods for the assessment of subsurface materials using the metal detection method. Metal detectors respond to the presence of both ferrous and nonferrous metals by inducing eddy currents in conductive objects. Metal detectors are either frequency domain (continuous frequency or wave) or time domain (pulsed) systems. A wide range of metal detectors is commonly available. 1.1.1 Metal detectors can detect any kind of metallic material, including both ferrous metals such as iron and steel, and non-ferrous metals such as aluminum and copper. In contrast, magnetometers only detect ferrous metals. 1.1.2 Metal detector measurements can be used to detect the presence of buried metal trash, drums (Tyagi et al, 1983) (1) and tanks, abandoned wells (Guide D6285 ); to trace buried utilities; and to delineate the boundaries of landfill metal and trench metal. They are also used to detect metal based unexploded ordnance (UXO). 1.2 Limitations : 1.2.1 This guide provides an overview of the metal detection method. This guide does not provide or address the details of the theory, field procedures, or interpretation of the data. References are included for that purpose and are considered an essential part of this guide. It is recommended that the user of this guide be familiar with the references cited and with the ASTM standards D420 , D653 , D5088 , D5608 , D5730 , D5753 , D6235 , D6429 , and D6431 . 1.2.2 This guide is limited to metal detection measurements made on land. The metal detection method can be adapted for a number of special uses on land, water, airborne and ice. 1.2.3 The approaches suggested in this guide for the metal detection method are commonly used, widely accepted, and proven. However, other approaches or modifications to the metal detection method that are technically sound may be substituted. 1.2.4 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project ’ s many unique aspects. The word “ Standard ” in the title of this document means only that the document has been approved through the ASTM consensus process. 1.3 The values stated in SI units are regarded as standard. The values given in parentheses are inch-pound units, which are provided for information only and are not considered standard. 1.4 Precautions : 1.4.1 It is the responsibility of the user of this guide to follow any precautions in the equipment manufacturer's recommendations and to establish appropriate health and safety practices. 1.4.2 If the method is used at sites with hazardous materials, operations, or equipment, it is the responsibility of the user of this guide to establish appropriate safety and health practices and to determine the applicability of any regulations prior to use. 1.4.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use. ====== Significance And Use ====== Concepts : This guide summarizes the equipment, field procedures, and interpretation methods for using the metal detection method for locating subsurface metallic objects. Personnel requirements are as discussed in Practice D3740 . Method — Metal detectors are electromagnetic instruments that work on the principle of induction, using typically two coils (antennas); a transmitter and a receiver. Both coils are fixed in respect to each other and are used near the surface of the earth. Either an alternating or a pulsed voltage is applied to the transmitter coil causing electrical eddy currents to be induced in the earth. The electrical currents flowing in the earth are proportional to electrical conductivity of the medium. Theses currents generate eddy currents in buried metallic objects that is detected and measured by the receiver (Fig. 1). Parameter Measured and Representative Values : Frequency Domain Metal Detectors : Frequency domain metal detectors apply an alternating current having a fixed frequency and amplitude to the transmit coil which generates a time-varying magnetic field around the coil. This field induces eddy currents in nearby metallic objects that in turn generate time-varying magnetic fields of their own. These eddy-fields induce a voltage in the receiver coil. The presence of metal causes small changes in the phase and amplitude of the receiver voltage. Most metal detectors amplify the differences in the receiver coil voltage caused by nearby metal and generate an audible sound or meter (analog or digital) reading. Ground conductivity meters (frequency domain metal detectors) measure the two-components of the secondary magnetic field simultaneously. The first is the quadrature-phase component which indicates soil electrical conductivity and is measured in millisiemens per meter (mS/m). The second is the inphase component, which is related to the subsurface magnetic susceptibility and is measured in parts per thousand (ppt) (that is, the ratio between the primary and secondary magnetic fields). ( 1 ) Conductivity Measurements (Quadrature-Phase Component) Metallic objects within a few feet of the surface will cause induced magnetic field distortions that will result in zero or even negative values of measured conductivity. Deeper metallic objects will cause less field distortion and lead to measured conductivities which are abnormally high in comparison to site background values. ( 2 ) Inphase Component Inphase measurements are more sensitive to metal than conductivity measurements. Thus, inphase anomalies may indicate the presence of metal at a greater depth than the conductivity measurements. Time Domain Metal Detectors : In time domain metal detectors, a transmitter generates a pulsed primary magnetic field in the earth. After each pulse, secondary magnetic fields are induced briefly from moderately conductive earth, and for a longer time from metallic targets. Between each pulse, the metal detector waits until the response from the conductive earth dissipates, and then measures the prolonged buried metal response. This response is measured in millivolts (mV). Equipment — Metal detectors generally consist of transmitter electronics and transmitter coil, power supply, receiver electronics and receiver coil. Metal detectors are usually single individual portable. Typical “ treasure-hunter ” metal detectors provide an audible signal and/or meter reading (analog or digital) when metal is detected. Quadrature and inphase measurements from ground conductivity meters are shown either on analog or digital meters. These measurements can often be recorded digitally in the field using a small field recorder, strip-chart recorder, or computer. Time domain metal detectors can consist of either one or two receiver coils. When two coils are used, one coil is typically placed above the other. Readings from both coils are recorded simultaneously. In order to improve detection of deeper metallic targets, the differential response from the two receiver coils can be used to suppress the response from smaller, shallower metallic targets. Some time domain metal detectors are mounted on wheels, allowing for the use of odometers to provide location data. Limitations and Interferences : General Limitations Inherent to Geophysical Methods : A fundamental limitation of all geophysical methods is that a given set of data cannot be associated with a unique set of subsurface conditions. In most situations, surface geophysical measurements alone cannot resolve all ambiguities, and some additional information, such as borehole data, is advised. Because of this inherent limitation in the geophysical methods, a metal detector survey alone can never be considered a complete assessment of subsurface conditions. Properly integrated with other geologic information, metal detector surveying is a highly effective method of obtaining subsurface information. In addition, all surface geophysical methods are inherently limited by decreasing resolution with depth. Limitations Specific to the Metal Detection Method : Several factors influence metal detector response: the properties of the target, the properties of the soil/rock, and the characteristics of the metal detector itself. The target ’ s size, depth, and condition of burial are the three most important factors. The larger the surface area of the target, the greater the eddy current that may be induced, and the greater the depth at which the target may be detected. The metal detector ’ s response decreases at a rate equal to the reciprocal of its depth up to the sixth power (1/depth 6 ). Therefore, if the distance to the target is doubled, the metal detector response will decrease by a factor of 64. Consequently, the metal detector is a relatively shallow-depth device. It is generally restricted to detecting small objects at relatively shallow depths or larger targets at limited depths. Generally, most metal detectors are incapable of responding to targets at depths much greater than 6 m. Although the shape, orientation, and composition of a target will influence the metal detector response, these factors will have much less influence than will the size and depth of the target. Target deterioration, however, has a significant impact. Metallic containers will corrode in natural soils conditions. If a container is corroded, its surface area will be significantly reduced, and in turn will degrade the response of a metal detector. Because the metal detector ’ s response weakens rapidly with increasing distance to the target, system gain and instrument stability are important. The size of the coil controls the size and depth of the metallic target that can be detected as shown in Fig. 2. Interferences Caused by Natural and Cultural Conditions : Sources of noise referred here do not include those of a physical nature such as difficult terrain or man-made obstructions but rather those of a geologic, ambient, or cultural nature that can adversely affect the measurements and hence the interpretation. Natural Sources of Noise — Some kinds of soil/rock, particularly those containing high iron content (often known as mineralized soil) affect receiver coil output strongly enough to indicate the presence of a metal target with certain kinds of metal detectors. Some types of metal detectors provide a means for compensating the output for the ground effect. This usually requires the operator to position the detector near the ground (but not near a metal target) and adjust a control until the target signal disappears. Small variations in the soil characteristics and stones (particularly those containing metallic compounds) can cause small changes in the detector output. Often these changes cause small target-like signals, known as “ ground noise. ” These can confuse the operator because they sound like small targets. Cultural Sources of Noise — Cultural sources of noise can include interference from electrical power lines, communications equipment, nearby buildings, and metal fences. Interference from power lines is inversely proportional to the distance between power line and detector; therefore most metal detectors with small coils are generally unaffected. Surveys should not be made in close proximity to buildings, metal fences or buried metal pipe lines that can be detected by the metal detection method, unless detection of the buried pipe line, for example, is the object of the survey. It is sometimes difficult to predict the appropriate distance from the potential sources of noise. Measurements made on-site can quickly yield the magnitude of the problem, and adjustments can then be made. Precaution must also be taken to remove metal from the operator, or to minimize its effects. Steel-toe boots, respirators, and air bottles can all cause considerable problems with noise. Summary — During the course of designing and carrying out a metal detection survey, the sources of ambient, geologic and cultural noise must be considered and the time of occurrence and location noted. The exact form of the interference is not always predictable, as it not only depends upon the type of noise and the magnitude of the noise but also upon the distance from the source of noise and possibly the time of day.