ULTRASONIC CONVERGENCE MEASUREMENTS.

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McVey, James R.
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ULTRASONIC TRANSDUCERS - Applications;
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Tests during pillar robbing, longwall operations, and other mining activities indicate that roof-floor convergence rates can be used as an indicator of imminent roof failure. New instruments provide nonobstructing measurements up to 35 ft away. The ultrasonic transducers can be attached to a roof bolt, placed in an unsupported area (by means of a toss basket), or handheld.
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