DYNAMIC CHARACTERISTICS OF AIR-FILLED DIFFERENTIAL PRESSURE TRANSDUCERS

Air-filled transducers were evaluated using step-function pressure inputs that allow a complete analysis of the signal distortion through the study of the transients. A square-wave pressure generator was used to produce step functions, the pressure signal being continuously monitored with a reference transducer tested with a shock tube. The step responses obtained from eight differential pressure transducers indicated a lag phenomenon, even in the absence of a conducting tube. From the analysis of the step response, the widely accepted second-order model was challenged; this conclusion is supported by harmonic tests. A curve-fitting analysis of the step response indicated that a satisfactory model of the transducer was obtained by use of a third-order equation, and, when a conducting tube was added, by a second-order equation plus a delay. Correction of the signal from differential pressure transducers was shown to be important even for low-frequency signals as encountered in the respiratory system.