| 摘要 |
In a pneumatic measuring device of the leakage input type, a shaft of uniform diameter moves in a reciprocal manner within a conformably shaped bore. The shaft and the bore are substantially of the same length so that if the shaft is moved axially the portion which is still encompassed by the bore is shortened. This annular passage between the shaft and the bore is used as a variable flow area. Pressure regulated compressed air on the upstream side of a line restriction is fed into a conduit which branches; one branch goes to a leakage input signal; the other branch goes to a chamber between the end of the shaft and the end bore; this chamber is closed except for the annulus. Opposing the movement of the shaft is either a weight (when the shaft and bore are pointed vertically) or a pneumatic cylinder. If the leakage input is varied the flow to the chamber between the shaft and the bore varies. As the pressure forces the shaft to move the annulus shortens, thereby admitting more flow until the force moving the shaft (the pressure X the area) is equal to the opposing force of the pneumatic cylinder or the weight. The output of the device is the axial movement of the shaft with sufficient power to operate switches and like operations.
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