High-precision measuring method and apparatus

Apparatus for monitoring a condition having a known relation to, or influence on, the transit time of movement of an energy wave through a medium, comprising:

• a transmitter for transmitting a cyclically-repeating energy wave through a transmission channel in said medium;
• a receiver for receiving said cyclically-repeating energy wave transmitted through said transmission channel;
• and a processor for continuously changing the frequency of transmission of the cyclically-repeating energy wave through said transmission channel in accordance with changes in the monitored condition while maintaining the number of waves in a loop including said transmission channel as a whole integer, and for utilizing the change in frequency to produce a measurement of said monitored condition.

A method of measuring the transit time of transmission of a cyclically-repeating energy wave moving through a transmission channel, comprising:

• continuously controlling the frequency of the transmission of said cyclically-repeating energy wave through said transmission channel such that the number of waves in a loop including the transmission channel is a whole integer;
• continuously measuring the frequency of the transmission;
• and utilizing the measured frequency of the transmission to provide a continuous indication of said transit time.