| 摘要 |
PURPOSE:To prevent malfunction due to the variance in a component characteristic and a temperature characteristic of the component by processing the direction and number of times of quadrant transition digitally. CONSTITUTION:An ultrasonic wave radiated by a transmitter 1 is reflected by a body and received by a receiver 2, whose receive signal Ein is frequency-converted by a converter circuit 20. A quadrant signal generating circuit 27 sends quadrant signals from output terminals I -V corresponding to the respective quadrants of the rotary vector of the receive signal Ein and a quadrant transition direction detecting circuit 31 outputs an L- or H- level digital signal according to the rotational vector of the signal Ein moves to another quadrant counterclockwise or clockwise. Quadrants are changed regardless of whether the output of the detecting circuit 31 is at the level H or L, and when the direction of the transition is inverted, a threshold value circuit 32 sends out a transition detection signal. Then, how many times the transition detection signal is generated in one cycle of the clock signal from a clock generating circuit 33 is counted and when the counted value is within a specific range, a decision output 35 outputs an alarm signal. |
