Measuring apparatus to determine the flow of a fluid

1. A measuring apparatus to determine the flow of a fluid, comprising a hollow body, which has an inflow and an outflow for the fluid and in which a magnetic sample including a permanent magnet is movably arranged which can be acted upon with a working pressure by the fluid, at least one position sensor to determine the position of the magnetic sample, an electromagnet to exert a magnetic force on the magnetic sample, and a control device for the electromagnet which is connected signal-wise to the position sensors, the control device including regulating means which control the electromagnet with the aid of a signal of the position sensor such that the magnetic sample is held in a position against the working pressure, the magnetic sample being designed and arranged such that the fluid can flow through the hollow body from the inflow to the outflow.

2. A measuring apparatus in accordance with claim 1 , in which the magnetic sample is held in a pre-settable position.

3. A measuring apparatus in accordance with claim 1 , in which the sample body is magnetized in the axial direction.

4. A measuring apparatus in accordance with claim 3 in which the sample is magnetized in opposite axial directions.

5. A measuring apparatus in accordance with claim 1 , in which the sample is magnetized in the radial direction.

6. A measuring apparatus in accordance with claim 1 , in which the hollow body has a circular flow cross-section.

7. A measuring apparatus in accordance with claim 1 , in which the flow cross-section of the hollow body varies in accordance with a pre-settable scheme along a longitudinal axis.

8. A measuring apparatus in accordance with claim 1 , in which the magnetic sample has one of a ring shape and a plate shape.

9. A measuring apparatus according to claim 8 wherein the magnetic sample has the shape of a circular plate.

10. A measuring apparatus in accordance with claim 1 , in which a cross-sectional area of the magnetic sample varies in accordance with a pre-settable scheme along a body axis.

11. A measuring apparatus in accordance with claim 1 , wherein the magnetic sample has at least one bore through which fluid flows in the operating state.

12. A measuring apparatus in accordance with claim 1 , which includes securing means to stabilize the position of the magnetic sample.

13. A measuring apparatus in accordance with claim 12 wherein the securing means stabilizes a radial position of the magnetic sample.

14. A measuring apparatus in accordance with claim 1 , in which a separate overflow line for the fluid connects the inflow of the hollow body to the outflow of the hollow body.

15. A measuring apparatus in accordance with claim 1 , in which the magnetic sample has a jacket.

16. A measuring apparatus in accordance with claim 1 , in which the magnetic sample has a position transducer to cooperate with the position sensor.

17. A measuring apparatus in accordance with claim 1 , in which the regulating means include an electronic regulator which is designed as a PI controller, as a PID controller or as a state controller.

18. A measuring apparatus in accordance with claim 1 , having an evaluation unit which determines the flow of the fluid through the hollow body with the help of the electrical energy required for the excitation of the electromagnet.

19. A method of determining the flow of a fluid by means of a measuring apparatus, which has:

a hollow body with an inflow and an outflow for the fluid and a magnetic sample with a permanent magnet movably arranged in the body;

an electromagnet to exert a magnetic force on the magnetic sample;

a control unit for the electromagnet which is connected signal-wise to at least one position sensor to determine a position of the magnetic sample, the method comprising

flowing the fluid through the hollow body from the inflow to the outflow such that the magnetic sample with the permanent magnet is acted upon by a working pressure generated by the flowing fluid, electrically controlling the electromagnet with the aid of a signal of the position sensor such that the magnetic sample with the permanent magnet is held in a position against the working pressure, and determining the flow of the fluid from the electrical energy required by the electromagnet for holding the magnetic sample with the permanent magnet in the position.

20. A method in accordance with claim 19 , including controlling the electromagnet such that the magnetic sample with the permanent magnet is acted upon with a constant working pressure independently of the flow of the fluid.

21. A method in accordance with claim 19 , including controlling the electromagnet such that the magnetic sample with the permanent magnet is acted upon with a constant working pressure in dependence on the flow of the fluid.

22. A method in accordance with claim 19 , wherein determining the flow comprises determining at least one of the position of the magnetic sample with the permanent magnet and a current through the electromagnet.

23. A method in accordance with claim 19 , including oscillating the magnetic sample with the permanent magnet about the axial position with the aid of the electromagnet, and from the oscillations of the magnetic sample with the permanent magnet determining a viscosity of the fluid.

24. A method according to claim 19 including determining at least one of a viscosity and a density of the fluid.

25. A method according to claim 19 including using the flow of the fluid for controlling at least one of a valve and a flow regulating system for a fluid.