The device works according to the paddle principle. The paddle is fixed on a bearing and protrudes into the flow. A magnet is attached to the opposite side. A second, external magnet repels the paddle magnet. This produces a restoring force.
This force may be set by changing the distance between the magnets by means of a screw so that the switching point of the device can be adjusted easily and precisely. A reed switch fixed to the outside is actuated contactfree by means of the magnet on the pendulum.