| The development of a portable digital electric spirometer with improved accuracy is described in this paper. A differential pressure sensor is used to detect the gas flow rate. The pressure sensor includes correction factor to compensate for temperature-related volume changes due to cooling of expired gas. Relation information between differential pressure and flow volume is analyzed by mathematical model, which is achieved by means of successive approximation algorithm by segment and implemented by using Visual Basic program. Reduction and selection of a parameter set is the purpose of the algorithm. Regression analysis shows that the properties of the airways were well approximated by exponential functions. Some other dependencies between mechanical quantities and flow volume were also included.The system includes a blocking unit which is different from traditional ones. The diameter of the blocking unit is less than traditional ones more. A differential pressure sensor (1210D-2psi) manufactured by 1C Sensors is used in this electric spirometer. Besides the signal detector (the sensor 1210D) which has a inside resistance to adjust amplifier gain, the system also includes the following hardware: an instrument amplifier, a sampling-holding unit which can decrease the sampling frequency, a negative to positive integral analog-to-digital converter, a EEPROM CMOS chip 24C01 to store revising parameter, a uP supervisor circuits MAX813L which provides four functions: a reset output; an independent watchdog output; an active-low manual-reset input; a 1.25V threshold detector for power-fail warning, a power unit TPS76050, a single chip microprocessor 78E58 manufactured by Winbond and a LCD display for portable instrument drove by HT1621 manufactured HOLTEK. Auto zero drift compensation is provided by addition of a signal having an adjusted DC value. The instrument is used to replace the existing old one. |
PDF Full Text Request