Abstract: The invention comprises a pressure actuated switch which is actuated when the inlet port of the device is exposed to a preselected pressure. A piston size, and one or more shear pins, is selected for the desired operating pressure, the piston area being inversely proportional to the desired operating pressure. Shear pins are preferably of one size and material. When the desired operating pressure is applied, the force of the piston causes the shear pin to shear thereby allowing an electrical contact to complete an electrical circuit and initiate operation of a selected device such as a recorder, perforating gun, etc. If a single shear pin is used, with any selected piston and desired operating pressure, the shear force applied is a constant; i.e., for any given operating pressure and selected piston size with a single shear pin, the applied shear force is the same. If two shear pins are required, the applied shear force is doubled.

Abstract: An external gauge carrier for use in tubing-conveyed drill stem testing comprises a protective housing for locating and securing the pressure measuring and recording system. The gauge carrier may be manufactured from drill collar bar stock but provides a 1--1 interface with ordinary drill pipe, other measurement subs, perforating guns and the like; i.e., to the complete system it "looks" like a drill collar. The gauge measures and records drill stem bore pressure while providing "full bore" testing capabilities, i.e., the gauge carrier allows unimpeded wireline operation therethrough and causes essentially no pressure drop throughout its length. Special machining and gauge placement is required in order to provide the above capabilities and features while still maintaining sufficient wall thickness to ensure structural integrity. A unique system for protecting the relatively delicate gauges from damage due to shocks from pressure surges is also disclosed.