A fluid-powered actuator comprises a cylindrical body having a base proximate one extremity and a head proximate another extremity, a piston-rod assembly and a sensor module made of a removable cover and a position sensor. The piston-rod assembly is slidably mounted inside the cylindrical body. The base is provided with an opening adapted to accommodate the sensor therethrough. In operation, the cover seals the opening. The position sensor is mounted to an internal face of the cover so that the position sensor is operatively located inside the cylindrical body when the cover is in place. The position sensor is operative to measure a position of the piston-rod assembly. A sensor module adapted to sealably close the opening in the base comprises the position sensor mounted to an internal face of a cover structure. In operation, the position sensor is operatively located inside the actuator when the cover structure closes the opening.