Digitized linearizing correction apparatus with frequency modulation

Abstract

A digitized linearizing correction apparatus has an input from a nonlinear responding thermocouple which produces a signal proportional to a temperature to be measured. An oscillator generates clock pulses at a first frequency which are fed to a counter and also are fed to a timing generator for alternately producing sample timing and count timing signals. A passive integrator receives the proportional signal during the sample timing signal and is discharged proportional thereto. A constant current source is coupled to the integrator during the count timing signal for charging the integrator at a constant rate. A comparator is coupled to the output of the integrator and also to a fixed referenced level for producing an output signal when the integrator is charged back to the reference level. The time from the start of the count timing signal until the integrator output signal is produced establishes a counting period. To accomplish linearizing, the timing generator causes the oscillator to change to a second frequency upon the attainment of a first predetermined number of clock pulses during the count timing signal. Similarly, upon the attainment of a second predetermined number of clock pluses during the count timing signal, the oscillator is caused to operate at a third frequency. Accordingly, the counting period is segmented into parts having respectively different frequency modulation to provide the desired linearization. The accumulated frequency modulated count of the clock pulses during the counting period is obtained for transfer to a display device as a reading of the measured temperature.