Influence of the Connecting Passage of a Low Pressure Indicator on Recording

Abstract

Since the pressure sensitive diaphragm of a low pressure indicator is usually made large to increase the gain per unit pressure, it is difficult to arrange the diaphragm to be flush with the inner surface of the wall, to which the indicator is fixed. The error, resulting from the passage leading from the inner surface to the diaphragm, increases with the decrease in the resonant frequency of connecting passage. The authors have theoretically and experimentally investigated the effect of the connecting passage on the accuracy of the pressure measured. They found out that the resonant oscillation in the connecting passage, which occurs due to the cross-sectional area of passage being made large to raise the resoant frequency, can be successfully avoided by fitting the passage with a damper such as a throttle. The delay of the measured pressure-change due to the damper is permissibly small.