Borehole extensometer

Claim 1

APPARATUS FOR MEASURING ROCK MOVEMENT IN A BOREHOLE COMPRISING: AN ANCHOR MEANS ADAPTED TO BE SECURED IN THE BOREHOLE AT A SELECTED POSITION THEREIN AND TO HOLD THE END OF A WIRE; A STRETCHABLE WIRE SECURED TO THE ANCHOR MEANS AND ADAPTED TO EXTEND TO THE MOUTH OF THE BOREHOLE; A SUPPORT HEAD AT THE MOUTH OF THE BOREHOLE; A CANTILEVER SPRING MEANS MOUNTED UPON THE HEAD AND LATERALLY DISPOSED WITH RESPECT TO THE WIRE, THE OUTSTANDING END OF SAID SPRING MEANS BEING ALIGNED WITH THE WIRE AND SAID SPRING MEANS BEING ADAPTED TO FLEX IN THE DIRECTION OF THE BOREHOLE AXIS; MEANS FOR CONNECTING THE WIRE WITH THE SPRING MEANS WITH SUFFICIENT TIGHTNESS TO STRETCH THE WIRE AND FLEX THE SPRING MEANS, WHEREBY THE WIRE AND SPRING MEANS ARE DEFLECTED TOGETHER AS AN ELASTIC SYSTEM RESPONSIVE TO CHANGES OF LENGTH OF THE BOREHOLE AND SAID SPRING MEANS REFLECTS BOTH CHANGES IN LENGTH OF THE BOREHOLE AND CHANGES IN WIRE TENSION CAUSED BY CHANGES IN THE LENGTH OF THE BOREHOLE; AND TRANSDUCER RECORDING MEANS INCLUDING A STRAIN GAUGE AFFIXED TO SAID CANTILEVER SPRING MEANS FOR MEASURING THE FLEXING OF THE SPRING MEANS, WHEREBY TO PERMIT DETERMINATION OF THE ROCK MOVEMENT, AS INDICATED BY CHANGING OF THE BOREHOLE LENGTH BETWEEN THE ANCHOR MEANS AND THE SUPPORT HEAD.