| 摘要 |
A position detector includes a fluid cylinder having a piston. An ultrasonic transceiver is provided at one end of the piston outside of the moving range of the piston. In response to electrical signals, the ultrasonic transceiver transmits ultrasonic waves to a reflection surface of the piston. The transceiver receives the ultrasonic waves reflected by the piston and then generates electrical signals representing the reflected waves. A sensor detects that the piston is at a predetermined position, at which the distance to the transceiver is known. A CPU supplies electrical signals to the ultrasonic transceiver to produce ultrasonic waves and receives electrical signals representing the reflected waves from the ultrasonic transceiver. The CPU then computes a piston position value, which is a function of the travel time from when an ultrasonic wave is transmitted to when the reflected wave is received and the speed of the waves. The CPU determines the speed of the waves when the piston is detected to be at the reference position. The CPU then computes the current position of the piston based on the speed of the waves and on a current reading of the travel time.
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