Abstract: A method for calibrating and linearizing the output of an instrument that includes a transducer having an output that is a nonlinear function of a property of interest of a fluid. The results of measurements performed on a plurality of transducers of the type to be used in the instrument are used to produce first and second equations which give the direct and inverse responses of a typical transducer. The results of further measurements on the particular transducer to be used in the instrument are used with the first equation to define how the second equation may be used to give accurate results with the particular transducer. The instrument is then calibrated and the results used with the second equation to produce an accurate linearized value for display as the output of the instrument.

Abstract: An improved gas volume calibration method and apparatus for use in respiratory gas analyzers. A control unit monitors the flow of calibration gas through the analyzer by monitoring the electrical signals produced by a gas turbine and a breath switch. During calibration, a known volume of calibration gas is repeatedly delivered to the analyzer from a calibration syringe at each of a number of different flow rates. On the basis of the information received from the turbine and the breath switch, the control unit generates and stores a piecewise linear approximation of the nonlinear characteristic of the turbine. This stored turbine characteristic is then made available during subsequent measurements to eliminate those volume errors which are associated with variations in the rate at which the sample gas is delivered, thereby affording measurements of improved accuracy.