Abstract: A tire-pressure monitor (13) comprising a pressure switch to be fixed to the periphery of the wheel rim (12) of vehicle wheels radially to the wheel axis is proposed, which pressure switch consists of a reference-pressure chamber (20) which is closed off towards the tire by an electrically conductive diaphragm (21). To close an electric circuit the diaphragm (21), when tire pressure is sufficient, is pressed onto a contact pin (22) inserted in an insulated manner into the reference-pressure chamber (20). To achieve an increase in the switching threshold as a function of speed, which increase can be determined in a defined manner, the diaphragm (21), free towards the tire, is provided with an elastic additional mass (30) which is applied over the surface to one diaphragm side and whose modulus of elasticity, in relation to that of the diaphragm (21) is less than one tenth.

Abstract: A tire pressure sensor for motor vehicles comprises a pressure switch which is actuated by the tire pressure for monitoring the tire pressure. The pressure switch has a reference pressure chamber which is closed in the direction of the tire by means of an electrically conducting diaphragm and carries a contact pin which is contacted by the middle area of the diaphragm in order to close an electric circuit when there is sufficient air pressure in the tire. In order to trigger an alarm signal during a leak in the reference pressure chamber a leakage check of the reference pressure chamber is realized in that an air gap is located between the contact pin and the middle area of the diaphragm when there is equal pressure on both sides of the diaphragm.

Abstract: A pressure pick-off for generating electrical signals comprises a reference pressure chamber which is oxygen-free, at least one pressure dependent deformable membrane closing the reference pressure chamber from a medium under pressure and supporting at least one electric sensor element, and a conductor located in the reference pressure chamber and connectable with a measuring current circuit, the conductor being formed so that during a leakage in the reference pressure chamber it is oxidized by penetrated oxygen so that it is electrically interrupted.