| 摘要 |
Method of determining a position of a moving piston (3a) in a cylinder (1), said method comprising emitting with the aid of an emitter (6) placed adjacent to the cylinder, at a first point in time (ti) an ultrasonic signal so that it propagates inside the cylinder and is reflected on the surface of the piston, receiving with aid of a receiver (7) placed adjacent to the cylinder, at a second point in time (t2), a first resulting ultrasonic signal which contains the result of the ultrasonic signal reflected on the piston, obtaining a filtered ultrasonic signal through comparing the first resulting ultrasonic signal and a reference signal, wherein the reference signal is a resulting ultrasonic signal received by a receiver at a reference time point (to) and wherein the reference time point is different from the second point in time (t2), and in a calculating unit calculating the position of the piston based on the filtered ultrasonic signal. |
