Sensing apparatus

A sensing instrument for detecting a substance to be detected, based on the variation of the natural frequency of a sensor oscillator, using the sensor oscillator, on the surface of which an adsorbing layer to adsorb a substance to be detected is formed, and of which natural frequency is varied by adsorption of the substance to be detected, said sensing apparatus comprising:

• a sensor oscillator circuit to oscillate said sensor oscillator;
• a reference clock generating part to generate a clock signal for sampling frequency signals from said sensor oscillator;
• an analog/digital converting part for sampling the frequency signal from said sensor oscillator by the clock signal from said reference clock generating part, and outputting the sampling value as a digital signal;
• a means for obtaining a rotational vector to obtain a real part and an imaginary part when performing a quadrature detection with a digital signal for a frequency signal corresponding to the output signal from the analog/digital converting part, and performing complex notation of the rotational vector rotating at an angular velocity corresponding to the difference of frequency between the frequency of the frequency signal and the frequency identified by the digital signal used for the quadrature detection;
• and
• a means for calculating the velocity of the rotational vector to determine the angular velocity of the rotational vector based on respective time series data of said real part and the imaginary part obtained by the means for obtaining the rotational vector.