| 摘要 |
PROBLEM TO BE SOLVED: To provide a vehicle detector of which the wrong detection of vehicles is decreased. SOLUTION: A control circuit 2 of an ultrasonic vehicle detector detects natural resonance frequency f0 of an ultrasonic vibrator 1, calculates transmitting frequency f1 different from the frequency f0 and gives a transmitting signal of frequency f1 to the vibrator 1. A signal generation circuit 7 is activated when the coincidence of frequency is secured between the receiving and transmitting signals and sets a vehicle detection signalϕ7 at its activation level in response to the receiving signal. Therefore no coincidence is secured between the receiving and transmitting signals when the vibrator 1 is wet by raindrops and a receiving signal of frequency f0 is produced, and accordingly the signalϕ7 is never set at its activation level.
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