Modeling, preparation and characterization of a pressure measurement system with customizable high-pass characteristic

We present a measurement system, capable of measuring a small changing pressure component additional to a much larger static average pressure. It comprises a commercially available differential pressure sensor and a custom-made pneumatic low-pass filter. The resulting overall system has a high-pass characteristic, which allows it to operate under conditions where the static pressure changes slowly but by a quantity that exceeds the measurement range of the differential pressure sensor alone. The pneumatic low-pass and the preparation of the pneumatic resistance, implemented using a thin glass capillary, are described in detail. A measurement set-up for characterizing the time constant of the measurement system and the calculation of the flow resistance of the capillary are presented. Measurement results of several capillaries are analyzed and compared to a simple model that describes the capillary flow resistance in terms of easily controllable parameters.