Pressure transmitter for detection of a variable relative to a process fluid

1. A pressure transmitter for detection of a physical variable relative to a process fluid, comprising:

a first and a second pressure-sensitive membrane suitable for interfacing with said process fluid;

a pressure sensor having a supporting body provided with a cavity inside which a third pressure-sensitive membrane is positioned, said third membrane having a first face and a second face operationally connected to said first and second membrane, respectively, so that the pressure exerted by the process fluid on said first and second membrane is transmitted to said third membrane causing displacement thereof with respect to a reference position;

an analysis and conditioning unit operationally coupled to at least one light source;

a first optical fibre having a first end operationally coupled to said at least one light source and a second end positioned at a pre-set distance from said first face;

a second optical fibre having a third end operationally coupled to said at least one light source and a fourth end positioned at a pre-set distance from said second face, said first and second optical fibres transmitting the light signals emitted by said source to said third membrane and the signals reflected by the third membrane to said analysis and conditioning unit, and said analysis and conditioning unit generating, on the basis of the reflected signals received, signals directly or indirectly indicating said physical variable;

a first fixed lens operationally combined with said second end of said first optical fibre, and a second fixed lens operationally combined with said fourth end of said second optical fibre; and

a first beam splitter suitable for splitting, within said first optical fibre, the light beams coming from said source into a first path which strikes said first face of the third membrane and a second path which strikes said first fixed lens;

wherein said first and second lens provide reflected optical reference signals that run in parallel with main measuring signals that are reflected by the first face and the second face of said third membrane, said reflected optical reference signals following separated optical paths from said main measuring signals.

2. The pressure transmitter as claimed in claim 1 , wherein said first fixed lens and said second fixed lens consist of a reflecting surface of said second and fourth ends respectively.

3. The pressure transmitter as claimed in claim 1 , wherein said first fixed lens and said second fixed lens consist of two corresponding reflecting surfaces positioned at a pre-set distance from said second and fourth ends respectively.

4. The pressure transmitter as claimed in claim 1 , comprising a second beam splitter suitable for splitting, within said second optical fibre, the light beams coming from said source into a third path which strikes said second face of the third membrane and a second path which strikes said second fixed lens.

5. The pressure transmitter as claimed in claim 4 wherein said first beam splitter and said second beam splitter are configured so as to direct towards said analysis and conditioning unit the reflected signals coming from said first face and second face of the third membrane and from said first and second fixed lenses.

6. The pressure transmitter as claimed in claim 1 , wherein said analysis and conditioning unit comprises, for each optical fibre, a first block for acquisition of the reflected signals received, a second block for measurement of the frequency and phase displacement between the signals received, a third block for combination of the signals received and a fourth block for the generation of a signal indicating the displacement of said third membrane.

7. The pressure transmitter as claimed in claim 5 wherein said analysis and conditioning unit comprises, for each optical fibre, a first block for acquisition of the reflected signals received, a second block for measurement of the frequency and phase displacement between the signals received, a third block for combination of the signals received and a fourth block for the generation of a signal indicating the displacement of said third membrane.

8. The pressure transmitter as claimed in claim 1 , wherein said analysis and conditioning unit is positioned remote and outside the supporting body.

9. The pressure transmitter as claimed in claim 1 , wherein said analysis and conditioning unit is positioned inside the supporting body.

10. The pressure transmitter as claimed in claim 1 , wherein said cavity of the supporting body has two shaped surfaces that can geometrically couple with said first or second face respectively of said third membrane.