A pressure gauge, comprising a pressure sensor (1, 47), a diaphragm seal, which is connected upstream of the pressure sensor (1, 47) and which comprises an isolation diaphragm, the outer side of which can be exposed to a pressure (p) and under which a pressure receiving chamber is enclosed, and a hydraulic pressure transmission path, which is connected to the pressure receiving chamber, is filled with a pressure transmitting fluid, and which transmits the pressure (p) acting on the outer side of the isolation diaphragm to the pressure sensor (1, 47), the diaphragm seal comprising an electronically activatable deflection device, which is designed such that, when activated, it exerts on the isolation diaphragm or on an element connected to the isolation diaphragm a constant force to deflect the isolation diaphragm, the isolation diaphragm being magnetic or ferromagnetic or being connected to a magnetic or ferromagnetic element, and the deflection device comprising an electronically activatable electromagnet, which, when activated, exerts on the isolation diaphragm or on the element connectable or connected thereto the force to deflect the isolation diaphragm, wherein a deflection measuring circuit which is connectable or connected to the electromagnet and is designed in such a way that it determines a deflection of the isolation diaphragm dependent on the pressure (p) acting on the isolation diaphragm when the deflection device is deactivated, on the basis of a property of the electromagnet dependent on the deflection of the isolation diaphragm, on the basis of an inductance of the electromagnet, or on the basis of a variable dependent on the inductance of the electromagnet; and a testing device, which is designed in such a way that it checks the functioning and/or the measuring accuracy of the pressure gauge when the deflection device is deactivated, on the basis of the pressure (p gem) measured by the pressure sensor and the deflection of the isolation diaphragm determined parallel thereto by means of the deflection measuring circuit. a pressure sensor (1, 47), a diaphragm seal, which is connected upstream of the pressure sensor (1, 47) and which comprises an isolation diaphragm, the outer side of which can be exposed to a pressure (p) and under which a pressure receiving chamber is enclosed, and a hydraulic pressure transmission path, which is connected to the pressure receiving chamber, is filled with a pressure transmitting fluid, and which transmits the pressure (p) acting on the outer side of the isolation diaphragm to the pressure sensor (1, 47), the diaphragm seal comprising an electronically activatable deflection device, which is designed such that, when activated, it exerts on the isolation diaphragm or on an element connected to the isolation diaphragm a constant force to deflect the isolation diaphragm, the isolation diaphragm being magnetic or ferromagnetic or being connected to a magnetic or ferromagnetic element, and the deflection device comprising an electronically activatable electromagnet, which, when activated, exerts on the isolation diaphragm or on the element connectable or connected thereto the force to deflect the isolation diaphragm, wherein a deflection measuring circuit which is connectable or connected to the electromagnet and is designed in such a way that it determines a deflection of the isolation diaphragm dependent on the pressure (p) acting on the isolation diaphragm when the deflection device is deactivated, on the basis of a property of the electromagnet dependent on the deflection of the isolation diaphragm, on the basis of an inductance of the electromagnet, or on the basis of a variable dependent on the inductance of the electromagnet; and a testing device, which is designed in such a way that it checks the functioning and/or the measuring accuracy of the pressure gauge when the deflection device is deactivated, on the basis of the pressure (p gem) measured by the pressure sensor and the deflection of the isolation diaphragm determined parallel thereto by means of the deflection measuring circuit.