OPTICAL MEASURING APPARATUS

PURPOSE:To realize a highly accurate optical measurement through a simple structure by controlling a motor for rotating an optical chopper with driving inputs in the same number as the chopper blades thereby synchronizing a drive signal with a detection signal to obtain an accurately synchronized reference signal. CONSTITUTION:An optical chopper 120 comprising three chopper blades 120a,..., 120c, for example, is driven through a step motor 160 to modulate infrared rays and the modulated infrared rays are detected by means of an infrared detection element 110. The three blades are subjected to rotational control with a three-phase drive input thus synchronizing a detection signal with a drive signal for the motor 160. A detection signal from the optical detection element 110 is amplified through a low noise amplifier 130 and then subjected to lock-in amplification through a lock-in amplifier 140 before being outputted from an LPF with a reference signal and harmonic components being removed therefrom. Since only a signal component is taken out, the highly accurate low noise optical measurement is realized. Simplification, small size and low power consumption are also realized because no photointerrupter is employed.