Patent ID: 9664043
Date: 2017-05-30
CPC Classifications: E21F,G01V,G08B

Claim:
1. A rock wall closure detection apparatus which includes: an elongate member, which is axially variably extensible between a first wall and a second wall of an underground excavation, comprising at least a first and a second segment which are resiliently axially compressible relatively to one another when the walls close; an indicator module attached to the first segment which includes a first and a second signal circuit, a first and a second signal device, a first and a second switch and a power source to power the circuits and the signal devices; an actuator attached to the second segment which includes at least one contact; wherein on compression of the member, the actuator moves relatively to the module between a first position, at which the at least one contact and the first switch are spaced, and a second position, at which the contact engages the first switch to actuate the first signal device to produce a warning signal; and wherein the first position is a position at which the at least one contact engages the second switch to actuate the second signal device to produce a second signal indicating that the apparatus is correctly pre-set.