Improved signal processor for the ultrasonic dimension gauge.

Inexpensive modifications and additions to improve the performance of a widely used ultrasonic dimension gauge are presented in detail. These include a pulse width demodulator, averaging peak detector, and improved signal processing circuits. Benefits of the modifications are improved frequency response (to 1 kHz), lowered drift, increased sensitivity (to 128 mV/mm), rational gain calibration, calibrated zero suppression, and improved recovery from signal dropout. The modifications result in the ability to take the derivatives of ventricular wall motion with greater reliability.