Bellows are tubular elastic sensitive elements connected with collapsible wrinkles along the direction of folding expansion. Bellows are widely used in a variety of instruments, one of its main USES is as a pressure measuring instrument measuring elements, pressure into displacement or force, suitable for measuring low pressure.

Bellows tube wall is thinner, the sensitivity is higher, the measurement range is tens of pa to tens of mega pa. The opening end is fixed, the sealing end is in free state, and the use of auxiliary spiral spring or reed to increase elasticity. When working, under the action of internal pressure, the tube extends along the length direction, making the moving end produce a displacement in certain relation with the pressure. The active end drives the pointer to directly indicate the pressure.

Bellows are also often combined with displacement sensors to form pressure sensors that output electricity and are sometimes used as isolation elements. The response speed of bellows is lower than that of bourdon tubes because the expansion of bellows requires large volume changes.

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