Ultrasonic anemometer

Claim 1

An ultrasonic anemometer, comprising: a first electro-ultrasonic transducer and a first ultrasonicelectric transducer arranged oppositely to each other at a predetermined sense direction; a second electro-ultrasonic transducer and a second ultrasonicelectric transducer arranged oppositely to each other at said predetermined space in the reverse direction to said sense direction of said first pair; means for simultaneously generating a train of successive ultrasonic pulses having a predetermined period from said first and second electro-ultrasonic transducers; a first signal receiving means connected to the output of said first ultrasonic-electric transducer to receive incoming ac signals corresponding to the ultrasonic pulses and comprising a zero-crossing detector for detecting zero-crossing instants of the ac received signals and for producing zero-crossing pulses in response to The zero-crossing instants, a multivibrator set by the first pulse of the zero-crossing pulses for each of the received ac signals and reset in synchronism with one of the zero-crossing pulses which coincides with a predetermined order number of cycles of each of the received ac signals, and a detector for detecting the resetting instant of the multivibrator as the incoming instant of each of the received ac signals; a second signal receiving means connected to the output of said second ultrasonic-electric transducer to receive incoming ac signals corresponding to the ultrasonic pulses and comprising a zero-crossing detector, multivibrator and detector alike those in said first signal receiving means;, a signal converter connected to said first signal receiving means and said second signal receiving means to obtain a pulse train the duration of each pulse of which is proportional to the time difference between said incoming instants respectively detected by said detector of said first signal receiving means and said second signal receiving means; and a pulse duration discriminator connected to said signal converter and comprising a saw-tooth wave generator for producing in response to each pulse of the pulse train a sawtooth wave which has a substantially constant slope and the duration of which coincides substantially with the duration of said pulse of the pulse train, a first capacitor for temporarily charging to the voltage of the saw-tooth wave after the termination of the saw-tooth wave, a bidirectional gate having two input terminals to one of which the charged voltage is applied, a generator for generating gating pulses each of which is timed with the termination of the saw-tooth wave and applied to the bidirectional gate, and a second capacitor connected to the other input terminal of said bidirectional gate to receive the charged voltage of said first capacitor so as to produce a discriminated output signal indicative of the velocity of the wind along said sense direction.