Abstract: The invention relates to the field of measuring instruments and, in particular to sensing apparatus capable of measuring displacement or deformation for the ultimate purpose of monitoring strain and/or stress. The vibrating wire measuring principle provides a very reliable method of measuring small deformations with high precision. Measurement apparatus utilizing this principle, however, tend to be limited in range to the elastic limit of the stretched wire. To increase the useful range of measurement of a vibrating wire monitor, a spring may be placed in series with the wire. In order to prevent the spring from vibrating during the resonancing of the wire and thereby delaying the determination of the wire's resonant frequency, the invention contemplates isolation of the spring from the wire in a vibrational sense. In one form of the invention, isolation is achieved by causing a nodal point to be formed on the spring side of the wire. The nodal point may be formed by pressing a fret against the wire.

Abstract: The invention relates to a device for monitoring strain or deformation within rock boreholes in three-dimension. The device comprises in general a vibrating wire strain monitor for monitoring strain or deformation in an axial direction with respect to the borehole axis interposed between two other vibrating wire string monitors which monitor strain or deformation in radial directions with respect to the borehole axis. The radial vibrating wire strain monitors each have elements by which they may be anchored within a borehole. Together, the three vibrating wire strain monitors monitor strain or deformation in three orthogonal directions within a borehole. The combination allows the axial vibrating wire strain monitor to utilize the radial vibrating wire strain monitor's anchors thereby eliminating their requirement to provide separate anchoring means therefor.

Abstract: A borehole strain monitor for soft rock consisting of a sensing unit, an installation/retrieval provision and a read-out unit. The sensing unit has a U-shaped yoke and is fitted with a vibrating wire transducer. A magnetically coupled variable frequency oscillator determines the point of resonance for the tensioned wire. The resonant frequency is measured with a frequency counter. The sensing unit is used, typically, in boreholes between two and six inches in diameter. The unit is firmly seated in the borehole by means of a pad at one side and a positively guided wedge at the other to bring the unit in contact with diametrially opposed portions of the borehole wall.

Abstract: A vibrating wire strain meter has a steel proving ring across the bore of which extends a taut wire. The outer surface of the proving ring has sloping or tapered grooves extending axially along the entire length of the ring. A pair of diametrically opposed wedges sloping at the same angle as the grooves are used to wedge the proving ring in a borehole. The tapered grooves provide positive guiding of the wedges such that the device can be positioned accurately and repeatably in relation to the borehole wall. Preferably, the wire extends across a diameter which is perpendicular to the diameter on which the grooves and wedges are located. A novel tool for inserting and withdrawing the strain meter is also described.