Patent ID: 7707891

Claim:
A pressure measuring cell comprising: a first housing body ( 1 ) made of ceramic material; a membrane ( 2 ) made of ceramic material and arranged proximate to said first housing body ( 1 ), said membrane being substantially planar and having a peripheral edge, the peripheral edge of said membrane ( 2 ) being joined by a first edge sealing material ( 3 ) to said first housing body ( 1 ) in such a way that a reference pressure chamber ( 25 ) is created between said first housing body ( 1 ) and said membrane ( 2 ), said membrane having first and second opposing surfaces, the first surface of said membrane ( 2 ) facing said first housing body ( 1 ) and said first housing body ( 1 ) having a surface facing said membrane ( 2 ); a second housing body ( 4 ) made of ceramic material and located opposite said membrane ( 2 ), said second housing body ( 4 ) being joined to the peripheral edge of said membrane by a second edge sealing material ( 3 ′), said second housing body ( 4 ) together with said membrane ( 2 ) forming a measurement pressure chamber ( 26 ), said second housing body including a port ( 5 ) for connecting the pressure measuring cell to a medium to be measured; said first housing body ( 1 ), said second housing ( 4 ) body and said membrane ( 2 ) being tightly connected along the peripheral edge of said membrane ( 2 ); and at least in the central area of the first housing body ( 1 ) a hole ( 7 ) is formed reaching through said first housing body ( 1 ) and at least in the central region of the membrane ( 2 ) and opposite the hole ( 7 ), a surface of the membrane ( 2 ) is formed as a first optically reflective area ( 10 ); an optical fiber ( 15 ) is arranged to bring light to and from the hole ( 7 ) of said first housing body ( 1 ) for feeding in and out light onto the surface of the membrane ( 2 ) and means are provided for forming a second reflective optical area for optical linking to said surface of the membrane ( 2 ) in such a way that in the arrangement between said means and the reflection area ( 10 ) of the membrane ( 2 ) an optical cavity ( 30 ) is present forms a measuring section for determining the level of deflection of the membrane ( 2 ) and which is part of a Fabry-Perot Interferometer detection arrangement; and wherein the surface of the membrane ( 2 ) at least in the region opposite to the hole ( 7 ) is covered by an extended flat glass spot which surface forms the first optically reflective area ( 10 ).