Protection system for the overpressures of a silicium wafer sensor used

Abstract

This invention relates to a system which protects against excessive pressure or overpressure being applied to a silicium wafer sensor fixedly mounted in a differential pressure transmitter between two wave separation membranes. The differential pressure arising between the two zones located astride and rigidly mounted silicium wafer sensor is controlled, so as to not exceed prefixed dangerous values, by a protection system having an expansion bellows located between the said two zones and polarized by a single pre-charged spring which is compressed when the bellows move. In one embodiment, the bellows is movable towards the low pressure so that the separation membrane is moved onto its respective seat which is part of the body of the transmitter only when the said differential pressure exceeds the precharge value of the said spring. Thus, within the measuring range of the transmitter, the protection system does not affect the measuring since it does not move, and therefore the measurement is practically effected without an appreciable displacement of the liquid and consequently an appreciable deformation of the separation membrane. On the other hand, for differential pressures exceeding the said measuring range and hence the pre-charge value of said polarization spring, the moving of the separation membrane of the high pressure side to its seat which is caused by the displacement of the expansion bellows towards the zone of the lower pressure, halts further increases of the high pressure and prevents transmission to the silicium wafer sensor. The differential pressure is thereby limited to the calibration value of the pre-charge of the said polarization spring.