Phase difference measuring apparatus and method

A phase difference measuring apparatus comprising:

• a signal wave detecting unit for obtaining a first receive signal by transmitting and receiving a signal in a reference state and for obtaining a second receive signal by transmitting and receiving a signal in a measuring state;
• a phase detecting unit for finding a reference phase difference .theta..sub.1 corresponding to a phase difference in the reference state and for finding an apparent phase difference .theta..sub.2 ' in the measuring state;
• phase difference correcting means for adding the apparent phase difference .theta..sub.2 ' to a product between the number of rotations, n, n being a number of times the apparent phase difference .theta..sub.2 ' passes through a reference point and an angle of 360.degree. to find a true phase difference .theta..sub.2 corresponding to an actual phase difference in the measuring state, the reference point including one angle in a variation range of the apparent phase difference .theta..sub.2 ';
• tendency detecting means for continuously detecting a direction in which the apparent phase difference .theta..sub.2 ' is increased or decreased;
• means for varying the number of rotations, n, to n=n+1 when the apparent phase difference .theta..sub.2 ' detected by the tendency detecting means is passing through the reference point while increasing;
• means for varying the number of rotations, n, to n=n-1 when the apparent phase difference .theta..sub.2 ' detected by the tendency detecting means is passing through the reference point while decreasing;
• and
• measured information outputting means for outputting state-measured information in the measuring state corresponding to an angle difference .DELTA..theta. between the true phase difference .theta..sub.2 and the reference phase difference .theta..sub.1.