What is an aneroid primarily known as in aviation instrumentation?

• A. The outer skin of a pressure-sensing element.
• B. The spring element of a pressure sensor.
• C. A sealed capsule made of corrugated metal used to accommodate pressure changes.
• D. The sensitive component in an altimeter or barometer that measures the absolute pressure of the air.

Answer: (D)

An aneroid is the sensing element that converts atmospheric pressure into a mechanical motion in aviation instruments. It is a sealed, flexible metal capsule (diaphragm) that deflects as the surrounding air pressure changes. In an altimeter or barometer, this deflection is translated through linkages into the instrument’s display, providing altitude or pressure readings. The essential idea is that the aneroid is the pressure-sensitive component, responding to the ambient air pressure (absolute pressure) and driving the measurement. It is not simply the outer casing or a separate spring, and while the capsule is a sealed, flexible container, its primary role is sensing pressure, not just housing or a structural element.