How does an aneroid barometer work?

Question

How does an aneroid barometer work?

Answer 1

In a mercury barometer,the atmosphereic pressure exerted on the level of mercury in a cistern is balanced by the column of mercury in a tube.Instead of using a cistern and mercury in this way ,if a flexible box (over which the atmospheric pressure is allowed to act) is used ,it can respond to pressure changes by setting in deformations.This principle is used in the construction of aneroid barometers,the word 'aneroid' meaning 'without liquid'.

Thus the sensitive element in this case is a partially exhausted disc shaped metal  box(called aneroid cell made of beryllium and copper) which undergoes changes of shape resulting from variations of pressure of the external air.

The ends of the box are usually corrugated to give more flexibility.A central spring prevents complete collapse of the box under the external pressure.The small movements of the box are transmitted by a system of magnifying levers to the pointer moving over a graduated dial indicating the air pressure.

Answer 2

An aneroid barometer uses a small, flexible metal box called an aneroid cell. This aneroid capsule(cell) is made from an alloy of beryllium and copper.[4] The evacuated capsule (or usually more capsules) is prevented from collapsing by a strong spring. Small changes in external air pressure cause the cell to expand or contract. This expansion and contraction drives mechanical levers such that the tiny movements of the capsule are amplified and displayed on the face of the aneroid barometer. Many models include a manually set needle which is used to mark the current measurement so a change can be seen. In addition, the mechanism is made deliberately 'stiff' so that tapping the barometer reveals whether the pressure is rising or falling as the pointer moves.They are used for measuring atmospheric pressure.