| 摘要 |
<p>A pressure switch having a movable bellows (14) in a pressure chamber (12), a first electrical contact (16) movable with the bellows, a three-dimensional cam (18) and a second electrical contact (20) resiliently biased to follow the cam. In the preferred embodiment of the invention, the cam has a radius that linearly increases with the angular position of the cam, and is tapered toward one end for all regions about its periphery except at a point of maximum-radius. Calibration at low pressure is effected by rotating the cam to its maximum radius point, applying a standard low pressure to the chamber (12) and rotating the chamber about a threaded coupling (26) until the contacts (16) and (20) are at the point of closing. Calibration at high pressure is effected by rotating the cam to its mimimum-radius point, applying a standard high pressure to the chamber, and adjusting the axial position of the cam until the contacts are at the point of closing. After such calibration, no recalibration is needed for intermediate pressure settings of the cam.</p> |
