| 摘要 |
PURPOSE:To detect a storke at a high accuracy by removing effect of temperature changes, variations in the composition of a working fluid, pressure changes and the like employing a propagation speed of an ultrasonic wave at the measuring point. CONSTITUTION:A first ultrasonic transmitter/receiver 2 for measuring distance adapted to transmit an ultrasonic wave toward a piston 3 and receive reflected waves is attached to a rear end wall 1a of a cylinder tube 1 while a second ultrasonic transmitter/receiver 4 for calibration to the surrounding wall at the rear end of the tube 1. A distance measuring circuit 5 determines an ultrasonic wave propagation speed C at the current time from the formula based on a time difference T2 between the transmission and reception of ultrasonic wave in the second ultrasonic transmitter/receiver 4 and the diameter dimension (d) of the cylinder tube 1 and executes computation of the formula based on the time difference T1 between the transmission and the reception of an ultrasonic wave in the first ultrasonic transmitter/receiver 2 to calculate the distance L between the end wall 1a and the piston 3. |
