Abstract: A cartridge forming a pressure measuring device is composed of main casing, a bushing detachably screwed to the casing and a coupling piece detachably screwed to the casing. The coupling piece has a plug which serves to establish hydraulic connection with some appliance to permit hydraulic fluid to act on a diaphragm configured as an integral thin wall of the coupling piece. A strain gauge sensor is mounted on the diaphragm and produces electrical signals on leads as the diaphragm deflects as a result of exposure to the pressure fluid. An amplifier serves to amplify the signals from the sensor for further processing and utilisation. The amplifier is mounted to the coupling piece with the aid of elongate conductive pins which also serve to connect the sensor leads to the amplifier.