Bellows are widely used in instruments and meters. The main purpose is to protect automotive wiring harnesses to convert pressure into displacement or force. The bellows has a thin wall and high sensitivity, with a measurement range of tens of Pa to tens of megapascals. . Its open end is fixed, the sealed end is in a free state, and the auxiliary coil spring or reed is used to increase the elasticity. During operation, it elongates along the length of the tube under the action of internal pressure, so that the movable end produces a certain relationship with the pressure. displacement.