A hydraulic pressure sensor is used for measuring the pressure in a hydraulic pressure chamber. Reservoir housing is connected to the pressure chamber, and the interior of the housing is divided by a slideable partition which defines a reservoir chamber which is connected to the pressure chamber and a sensor chamber which is connected to a sensor element. The partition is constructed as a piston and extends for sliding movement along the walls of the reservoir housing while exerting a frictional force. A spring supports the partition relative to the reservoir housing against the pressure in the reservoir chamber. The partition may be constructed as a differential piston, and consist of two or more piston sections which extend independently of one another in a sliding and sealing manner, and mutually support one another by an intermediate spring.As a specific example for protecting pressure sensors, in particular against pressure fluctuations, pressure surges, and pressure jumps, it has been proposed to connect the sensor chamber via a hose to the pressure chamber. This hose is made of an elastic material. In this connection, the hose acts as a reservoir, which absorbs and damps sudden pressure fluctuations, pressure surges, and pressure jumps on the one hand by its volume and on other hand by the elasticity of its sidewall? the disadvantage of this measure lies in that the hose connection is susceptible to damage, ageing, and leakage. Furthermore in many cases, it also represents an obstacle. This applies in particular to pressure sensors on working cylinders for development machines in mining, where it is necessary to consider pressures of more than 200 bars with pressure fluctuations and pressure surges of more than 100 bars.
A hydraulic strain sensor for use with a downhole tool includes a housing having two chambers with a pressure differential between the two chambers. A mandrel is disposed in the housing. The mandrel is adapted to be coupled to the tool such that the weight of the tool is supported by the pressure differential between the two chambers. A pressure-responsive sensor in communication with the one of the chambers is provided to sense pressure changes in the chamber as the tool is accelerated or decelerated and to generate signals representative of the pressure changes. In general, in one aspect, a hydraulic strain sensor for use with a downhole tool comprises a housing having two chambers with a pressure differential between the two chambers. A mandrel disposed in the housing is adapted to be coupled to the tool such that the weight of the tool is supported by the pressure differential between the two chambers. A pressure-responsive member in communication with one of the chambers is arranged to sense pressure changes in the one of the chambers as the tool is accelerated or decelerated and to generate signals representative of the pressure changes.
