| 摘要 |
The present invention is intended to provide an ultrasonic range finder to measure a distance quickly and precisely under different environments. The ultrasonic range finder comprises a casing 12 , an ultrasonic transmitting/receiving unit 20, a signal processing circuit connected electrically with the ultrasonic transmitting/receiving unit in the casing, a group of operation buttons (Fig 1, 13) on the casing and a display unit (Fig 1, 14). The ultrasonic range finder further comprises a calibration rod to provide a constant reference distance. The calibration rod 30 includes a first end 302 connected within the casing. The calibration rod further includes a second end 304 telescopically extendable outwardly relative to the casing and a body between the first and the second ends. By measuring a propagation time of an ultrasonic signal within the constant reference distance an ultrasonic propagation speed can be determined quickly and precisely and thereby perform the distance measurement quickly and precisely without being affected by changes in the environment. In a further embodiment a position reference can be provided to cooperate with the calibration member. (Fig 5).
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