A Standard Pressure Source for Calibrating Physiological Pressure Transducers

Abstract

In common with all measuring instruments, pressure transducers should from time to time have their performance checked. Sensitivity, together with zero offset checks, must be considered only an essential minimum, and for confidence in the results of these measurements it is also necessary to look at linearity and hysteresis. Of course, factors such as natural frequency and damping are also important in practice, but are more dependent upon the hydraulic arrangements associated with the transducer than any quality of the transducer itself that is likely to vary appreciably. Thus, the equipment to be described is concerned only with the ‘static’ measurements mentioned. Although a zero offset check is a simple matter, measurement of the other factors requires a pressure source that can be set to two accurately known values in addition to zero (relative to ambient), and temporarily to some value below ambient for checking hysteresis. Such tests can be carried out using liquid column type manometers, but they are not always convenient in a clinical environment. Moreover, the widely used mercury sphygmomanometer has only to be accurate to within k 2 mmHg to meet British Standard requirements, and unless properly maintained can be appreciably worse than this. The equipment to be described, based on the principle of the deadweight tester, is an attempt to overcome these problems.