VIBRATING WIRE STRESS METER METHOD TO CLAMP WIRES

摘要

A vibrating wire stress meter and the method used to clamp its wire in position. The wire is highly tensioned diametrically across the sides of a hollow metallic cylinder and held there by two anchor tubes. A wedge and platen assembly in turn hold this cylinder in a rock borehole such that small stress changes in the surrounding rock cause the diameter of the cylinder to slightly change. This cylinder variation is transmitted to and measured by the preloaded wire by noting variations in its frequency or period of vibration. To cause the wire to vibrate a coil, magnet, and yoke are used as a plural pole electromagnetic plucker. Clamping of the wire is accomplished by highly tensioning the wire between two opposite hollow tubes that are seated in opposited aligned countersunk holes of the cylinder and then extruding the steel tubes around the wire. The wire extends through holes of those hollow tubes as well as the aligned holes in the cylinder walls which are diametrically opposite each other. A harder punch with a hole in it to fit over the wire is forced against one of the recessed tubes to cause its material to plastically flow around the wire and into the sides of the cylinder hole. By doing this to both tubes and controlling the amount of force used in the punch operation the tension in the wire can be precisely controlled.