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Technology News 421 - software for interactive acquisition and analysis of time domain reflectometry measurements.

Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 421, 1993 Jul; :1-2
Objective: As part of the U.S. Bureau of Mines (USBM) program to characterize subsidence, this combination of software and hardware has been used to remotely monitor overburden response to longwall mining. Background: The principle of time domain reflectometry (TDR) is being used by the USBM to monitor strata displacements induced by mining. This capability has been enhanced by the availability of cable testers with serial communication modules that allow users to get TDR records in digital form. Actual field installations involve coaxial cables that are hundreds of meters long, and the many records obtained when monitoring such long cables on a daily basis motivated development of software to view interactively and compare waveforms and to analyze signature changes. Time domain reflectometry (TDR) was developed in the 1960's as a method to locate discontinuities in coaxial transmission cables. The concept has been extended to measurement of properties of materials into which probes are embedded, such as water content of soil, and evaluation of coaxial cable dielectric behavior. This technique was adapted by the USBM in 1978 for use in checking the movement of rock during underground mining. Coaxial cables are grouted into a rock mass that is expected to cave, and progressive rock movement causes the cable to deform. Consequently, there is a progressive change in cable electrical properties that produces changes in TDR pulse reflection signatures. TDR technology has been advanced by Northwestern University to the point where it is now possible to distinguish shear deformation from tensile deformation, and to quantify rock mass displacements, by analyzing these changes in TOR signatures. Approach: The Northwestern University TDR Signature Analysis (NUTSA) Program was developed under contract with the USBM to allow for visual comparison of three TDR waveforms quickly and easily. It is interactive, and on-line help is available. NUMOO (Northwestern University Remote Control TDR Data Acquisition System and Modification of Tektronix' SP232 Host Application Program) was then developed using commercially available software to allow acquisition of TDR waveforms from a remote cable tester via modem. How It Works: The program is documented in USBM Information Circular (IC) 9346. The IC details components of the data acquisition system and uses an interactive example to demonstrate NUTSA. TOR records are selected and displayed, then information is obtained by moving a cursor along the waveforms. The cursor location and waveform amplitude are indicated and additional information is obtained by using various commands. When the "Difference" command is invoked, NUTSA computes the arithmetic difference between data points of two waveforms and the difference waveform is displayed. When the cursor is positioned at the apex of a spike and the "View Difference Info" command is invoked, the spike width is computed and displayed. When the "Save Difference Info" command is invoked, the computed values are stored in an ASCII me for use with correlations between TDR signature characteristics and cable deformation. The limitations of this algorithm and continuing developments are discussed.
Mining-industry; Underground-mining; Coal-mining; Computer-software; Mines-Excavations; Settling; Measurement; Data-analysis; Data-acquisition; Interactive-systems; Subsidence; Computer-applications
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Technology News
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Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 421