| 摘要 |
A hydraulic ram 11 has a piston rod 22 reciprocable relative to a cylinder. The piston rod 22 is provided with a plurality of longitudinally- spaced permanent magnets embedded therein. Two sensors 25 and 26 are provided for sensing movement of the magnets, and hence relative movement between the piston rod 22 and the cylinder. The arrangement is such that any pair of adjacent magnets are sensed by different sensors 25 and 26. The magnets may be in single or double rows. In a single row, the outermost pole of each in the rod alternates. In a double row, one may have south poles the other north poles, or both rows may have the same poles. Magnets 30, 31 denoting end positions are provided. <IMAGE> |
