Sensitive Null-Balance Pressure Transducer

Abstract

A pressure transducer is described which operates by balancing the pressure to be measured with that due to a known hydrostatic head. The precision is ±0.0025 psi over a range of about 1 psi with less than 0.0025-psi drift in 8 h, and it requires very small fluid displacement. However, it can be used only where response to frequencies above about 0.2 cps is not required. A differential transformer monitors the height of the meniscus in one arm of a flexible, mercury-filled U tube. This meniscus is displaced by changes in pressure transmitted hydraulically from a sensing head. The output of the transformer controls a servomechanism that continually restores the meniscus to its original height by raising or lowering the other arm of the U tube. Changes in pressure within the sensing head thus cause proportional changes of height of the mobile arm of the U tube, which are monitored and recorded.