Tunnel roof monitor employing an induction coil extensometer

Details Tunnel roof monitor employing an induction coil extensometer Tunnel roof monitor employing an induction coil extensometer

1979-11-13

1981-06-02

Swann, III, Glen R.

Communications: electrical

Condition responsive indicating system

Specific condition

73784, 331 65, G08B 2100

Patent

active

042714079

ABSTRACT:
A ferrite core is suspended from the base of a borehole in a tunnel roof structure and is positioned within coil turns located at the roof surface such that movement of the roof structure causes displacement of the core with respect to the coil turns thus producing a change in inductance. The coil and core are incorporated as a frequency-determining element in an LR oscillator. Therefore, movement of the tunnel roof structure is reflected as a change in the frequency of the oscillator. This frequency is monitored and, if the change exceeds a predetermined threshold, an alarm is given. Several methods of suspending the core in the coil are disclosed, one of which allows for a non-verticle borehole.

REFERENCES:
patent: 3046535 (1962-07-01), Philbin et al.
patent: 3111655 (1963-11-01), Kotarsky et al.
patent: 3594773 (1971-07-01), Conkle et al.
patent: 3735244 (1973-05-01), Gumtau et al.
patent: 3891918 (1975-06-01), Ellis
patent: 3960009 (1976-06-01), Roepke et al.
patent: 3973191 (1976-08-01), Zabler
patent: 4156236 (1979-05-01), Conkle

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