地下探测用金属探测法使用指南

详细信息   

• 标准号：ASTM D7046-2011
• 发布日期：2011
• 英文题名：Standard Guide for Use of the Metal Detection Method for Subsurface Exploration
• 英文主题词：frequency domain ; geophysics ; metal detection ; metal detector ; subsurface investigation ; surface geophysics ; time domain ; Geophysical investigations/geophysics ; Metal detection/metal detector ; Subsurface investigation--soil/rock
• 标准状态：现行
• 发布单位：US-ASTM
• 国际标准分类号：13.080.99 (Other standards related to soil quality)
• 载体形态：8P.;A4
• 中国标准分类号：D10
• 国别：美国材料与试验协会

文摘

alic">alic">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 alidateSubscription.cgi?D3740-HTML">D3740.

alic">alic">Method8212;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).

alic">alic">Parameter Measured and Representative Values:

alic">alic">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).

(alic">1) alic">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.

(alic">2) alic">Inphase ComponentInphase 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.

alic">alic">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).

alic">alic">Equipment8212;Metal detectors generally consist of transmitter electronics and transmitter coil, power supply, receiver electronics and receiver coil. Metal detectors are usually single indiv........