Empirical investigation of noise reduction filter for a flow-based spirometer accuracy improvement

A turbine spirometer with an IR rotary encoder is designed and fabricated for performing Respiratory Function Tests (RFT). The system includes a hardware for gathering breath inspiratory flow rate and a user software which represents analyzed data of patients' breath flow and volume parameters in real-time. A major challenge in design of flowbased spirometers is the accuracy of device in measuring volume parameters of RFTs which is due to large effects of sensing data error and noise. The purpose of the paper is evaluating the efficiency of three different types of digital noise reduction filters in term of improving the accuracy of system in calculation of air volume passing through the spirometer turbine by use of data obtained by the innovative flow sensor. Three distinct kinds of flow waves are experimented and the most sufficient filter for corresponding respiratory function tests are reported.