A pressure sensor for measuring a pressure p contains a membrane with a front and a rear clamped into a body. The pressure p can be applied to the rear of the membrane. The front of the membrane is actively linked to a piston. In addition, a force transmitter is present with which a predetermined force can be applied to the piston. For the purpose of re-calibration, the membrane of the pressure sensor can be deformed by the force transmitter under precisely defined conditions and the output signal re-calibrated. A positioner can also be foreseen instead of the force transmitter.