Phase locked detector

Apparatus for detecting a change in position of an object in a field comprising:

• a transmitter for generating a transmit signal toward the object;
• a variable frequency oscillator for generating a modulation signal;
• means for modulating said transmit signal with said modulation signal to generate a modulated transmit signal;
• a receiver for receiving a reflection signal of said modulated transmit signal from the object;
• means for demodulating said reflection signal to generate a demodulated reflection signal;
• phase comparator means connected to receive said demodulated reflection signal and said modulation signal for generating an output signal applied to said variable frequency oscillator to control the frequency of said modulation signal to thereby maintain a predetermined phase relationship between said modulation signal and said demodulated reflection signal, such that the frequency of said modulation signal depends on the distance between the object and said transmitter;
• and
• means connected to said phase comparator means for continuously monitoring said output signal to provide an indication of a change in position of the object in the field.

A range finder for determining the range to an object comprising:

• a variable frequency transmitter for generating a transmit signal toward the object;
• a receiver for receiving a reflection signal at a first and second position of said transmit signal from the object, the distance between said first and second positions differing by a predetermined distance;
• phase comparator means connected to receive said reflection signal and said transmit signal for generating an output applied to said variable frequency transmitter to control the frequency of said variable frequency transmitter to thereby maintain a predetermined phase relationship between said transmit signal and said reflection signal when said receiver is located at said first and second positions;
• means for moving said receiver between said first and second positions;
• means for calculating a difference frequency, being the difference between said transmit frequency generated by said variable frequency transmitter when said receiver is in said first position and when said receiver is in said second position;
• means for determining the range to the object by calculating a ratio between said transmit frequency generated by said variable frequency transmitter when said receiver is in said first position increased by a factor of said predetermined distance between said first and second positions and said difference frequency;
• and
• means for displaying the calculated range to the object.

A method for detecting position changes of an object in a field comprising the steps of:

• generating a transmit signal at a transmitting station toward the object;
• receiving a reflection signal of said transmit signal from the object;
• controlling the frequency of said transmit signal to maintain a predetermined phase relationship between said transmit signal and said reflection signal such that the frequency of said transmit signal depends on the distance between the object and said transmitting station;
• and
• continuously monitoring the frequency of said transmit signal to provide an indication of a change in position of the object in the field.

A method for measuring the range to an object comprising the steps of:

• generating a transmit signal;
• receiving at a first location a reflection signal of said transmit signal from the object;
• varying the frequency of said transmit signal to produce a first frequency having a predetermined phase relationship between said transmit signal and said reflection signal;
• receiving at a second location, being a predetermined distance from said first location, said reflection signal of said transmit signal from the object;
• varying the frequency of said transmit signal to produce a second frequency having said predetermined phase relationship between said transmit signal and said reflection signal;
• determining the range to the object by using the relationship ##EQU2## where:
• d is the range to the object;
• .alpha. is said predetermined distance between said first location and said second location;
• .lambda..sub.1 is the wavelength of said first frequency;
• and
• .lambda..sub.2 is the wavelength of said second frequency;
• and continuously displaying the range to the object.