Absolute Pressure Capsules are partially evacuated and are hermetically sealed. They are used for barometric or altitude measurements.

Travel

Depending on hardness, thickness, shape and diameter of the material used, capsules change their height when under pressure and this change is reproducible. The distance by which the height changes is called 'Travel'. Depending on the application this travel may be taken up by a gauge movement, sender or switch. The travel of a diaphragm capsule can extend up to 5 millimetres or 0.2". lf this is not sufficient for a particular application two or more capsules may be stacked and their individual travels can be combined.

For further information about standard diameters of Beck's capsules please see the chart below.

Depending on the specific requirements, the travel of these diaphragms and capsules can be made linear or non-linear (e.g. for altitude measurements where the travel is linear in relation to the altitude and not in relation to the pressure).

Material

The selection of suitable materials is extremely important and depends on the requirements. For design reasons they can be plated. For absolute pressure capsules are mainly used: Copper Beryllium (CuBe2) which can be hardened, and Nickel Silver which cannot be hardened.

Capsules for altitude meters