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Abstract

A method of measuring the thickness of test articles by pulse reflection ultrasonics, the length of time period as determined by the signal triggering the ultrasonic transmission and by an ultrasonic signal reflected at the end of the measurement path length being used to determine the distance travelled by the ultrasonics. In the method, the triggering signal for the ultrasonic transmitter is generated in phase with a measuring oscillation of a high and known frequency, whereafter the integral number of measuring oscillation pulses or waves which fit into a time period corresponding to measurement path length are counted, whereafter the measuring oscillation is so detuned that the residual measuring oscillation or wave found over and above that in the time period is reduced to zero and a correction value is derived from the amount of frequency detuning for the measurement path length resulting from the integral number of measuring oscillation pulses or waves. This method and apparatus make possible high accuracy of measuring while avoiding the disadvantages of analog circuit arrangements and while using a counting frequency usable by very low current CMOS components which can be used in portable battery-operated devices.

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First Claim