Phase measurement apparatus with automatic calibration

A phase measurement apparatus with automatic calibration, comprising:

• first and second connection terminals connected to an object to be measured in a phase measurement mode;
• a calibration member connected in place of the object between said first and second connection terminals in the phase calibration mode, said calibration member being adapted to have at least linear frequency vs. phase characteristics;
• mode selecting means for selecting the phase measurement mode or a phase calibration mode for the object or said calibration member to be connected between said first and second connection terminals, said mode selecting means being adapted to generate an instruction for a selected mode;
• frequency setting means for receiving the instruction corresponding to the selected mode and generating variable frequency setting data corresponding to the received instruction;
• variable frequency signal generating means for receiving the variable frequency setting data corresponding to the received instruction and generating a variable frequency signal corresponding to the received variable frequency setting data, said variable frequency signal generating means being connected to said first connection terminal to supply the variable frequency signal to the object or said calibration member;
• phase difference detecting means connected to said first and second connection terminals to detect a difference between an input phase and an output phase of the variable frequency signal supplied to the object or said calibration member;
• variable amplifier means for receiving a phase difference detection signal from said phase difference detecting means and amplitude setting data, and amplifying the detection signal at a variable amplitude determined by the amplitude setting data;
• display means for receiving the phase difference detection signal amplified by said variable amplifier means and displaying the amplified phase difference detection signal;
• first and second phase ratio operating means for receiving the instruction for the phase calibration mode from said mode selecting means, and fetching, in response to the phase calibration mode instruction, the phase difference detection signal amplified by said variable amplifier means and the variable frequency setting data from said frequency setting means to perform predetermined operations, said first phase ratio operating means including means for calculating a first frequency vs. phase difference ratio between at least first and second frequencies of the variable frequency setting data, the first and second frequencies being determined such that the phase difference detection signals have a single level, said second phase ratio operating means including means for calculating a second frequency vs. phase difference ratio between at least third and fourth frequencies of the variable frequency setting data, the third and fourth frequencies being determined such that the phase difference detection signals have first and second levels;
• phase ratio comparing means for comparing outputs from said first and second frequencies vs. phase difference ratio calculating means;
• and
• amplitude setting means for receiving comparison results from said phase ratio comparing means and generating and supplying the amplitude setting data to said amplifier means such that the comparison result is substantially zero.