Richard I Willing

US Patent:

49598040, Sep 25, 1990

Filed:

Jul 12, 1988

Appl. No.:

7/217806

Inventors:

Richard S. Willing - Granada Hills CA

Assignee:

Baxter International Inc. - Deerfield IL

International Classification:

G01K 700
G06F 1520

US Classification:

364557

Abstract:

A parameter measuring apparatus includes a constant signal circuit incorporating a sensor having a known response to a given parameter for outputting a signal representing the parameter. The constant signal circuit further includes circuitry defining upper and lower limits of the parameter range. The parameter signal is provided to a sampling device such as current-to-frequency converter for providing an analog-to-pulse converted signal to a microprocessor. The apparatus further includes a switching arrangement coupled to and controlled by the microprocessor for switching into circuit the sensor or the circuitry defining the upper or lower parameter limits. The switching arrangement also eliminates internal switch resistance in the circuit for improved measurement accuracy. With the known response of the sensor as well as known regression analysis correction calculations stored in the microprocessor, the microprocessor outputs a corrected parameter signal which accurately represents the measured parameter regardless of variation in circuit operation due to changes in operating conditions.