Computer-Operated Impedance Stability Measurement System

The impedance of inductors, particularly those having fenite cores, is known to vary with frequency, temperature, ac signal level, dc bias, magnetic history (i.e., magnetization and demagnetization), and time. Obtaining the necessary statistical characterization data for these variations would be impractical with a manual measurement system. To meet this need a computer-operated, high-resolution impedance stability measurement system to characterize two-terminal passive elements was developed. The measurement system described consists of a general-purpose digital computer and three independent test stations operating in a time-shared mode. It is capable of unattended measurements to provide characterization of up to 24 samples per station with some measurements lasting as long as two weeks. Its accuracy and resolution are indicated by its capability of measuring temperature coefficients of 10 ppm/°F to within 1 ppm/°F. Topics presented are: system description; operator-system interaction; use of the computer for control, calculation, and data reduction; measurement technique and accuracy; and representative measurements.