A bellows refers to a tubular elastic active element that is joined in a folded elastic direction by a foldable crepe sheet. Bellows are widely used in instrument surfaces and are primarily used as measuring elements for pressure measuring surfaces to convert pressure into displacement or force. The wall of the bellows is thinner and has a higher degree of activity. The measurement plan is tens of kPa to tens of megapascals. Its open end is fixed, the sealed end is in a safe condition, and the elastic is added using an auxiliary coil spring or reed. During the operation, the internal pressure is extended along the length of the tube, so that the movable end is in a certain contact with the pressure. The movable end can directly indicate the size of the pressure by driving the pointer. Bellows are often combined with displacement sensors to form a pressure sensor that outputs electricity, sometimes as a barrier element. Because the expansion of the bellows requires a large volume change, its response speed is lower than that of the Bourdon tube. The bellows is suitable for measuring low pressure.
