SPEED SENSOR

摘要

A speed sensor 21 comprises a static part 3 and a dynamic part 5 arranged concentrically inside it. The static part 3 has two permanent magnets 7A and 7B and the dynamic part 5 has two iurther permanent magnets 9 and 11. The magnet 9 is oriented reversely to the iurther magnets 7A, 7B and 11. The magnets are tuned to each other so that gravity on the dynamic part is counteracted by the magnetic force on the dynamic part. As a result, the weight of the dynamic part need not be carried by springs and the dynamic part can move freely so that the full stroke can be used for measuring accelerations and the natural frequency is low. The static part 3 further includes a measuring coil 15 for measuring the displacement of the dynamic part and for the radial positioning of the dynamic part this part is connected to the static part 3 by means of leaf springs 17.