A resistivity meter is an instrument that measures how strongly a substance or material resists an electrical flow or current. It is used most often in geophysical surveys to measure the variances in the electrical resistance of the earth. A substance that measures a low resistivity is considered a good conductor of electrical energy. A poor conductor of energy will demonstrate a higher measurement of resistance to electrical currents through the material. These types of meters are relatively simple devices that can be enormously helpful in determining the properties of the soil and earth being surveyed. Engineers, miners and environmental specialists depend on this device to know what type of earth they are dealing with. Borehole logs are analyzed to determine the density of the material in the earth. A borehole is drilled for many reasons, including the removal of water and gases for mining expedition and exploration, environmental investigation and as a pilot hole for installing piers or underground utilities. Samples collected from borehole logs are sent to a laboratory for testing to determine a ground sections physical properties, or possibly to check for different chemicals or contaminants. These meters can measure much of these substances before they go to the lab. This way only the necessary samples are sent. Basic physics are the beginnings of any geophysical survey. Coal usually has a high resistivity measurement as opposed to other types of sedimentary rocks. Boreholes are have been used since the early 1930's to determine the ground properties of an area. These meters have improved the testing abilities for engineers. The detection of vacancies in the earth depends on whether or not there is a physical difference with the neighboring rock. If the vacancy is barren, it will be hard to find with electrical measurements. Air doesn't transmit electricity. The fact is that coal mines are not usually dry. The mine does not need to contain very much water for the openings to be detected by a resistivity meter. Advanced Geosciences. Inc. is a manufacturer of geophysical resistivity meter and IP imaging systems. (http://www.agiusa.com)
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