PQWT TC900 Geophysical Underground Water DetectorPQWT TC900 Geophysical Underground Water Detector Depth: 1200 meters (3938 ft) PQWT TC900 automatic mapping water detector is based on the Earth's electromagnetic field as the field source, based on the difference in the conductivity of different underground geological structures, and by studying the variation law of the electric field components at different frequencies to study the geological structure and changes, to find groundwater resources by