Electromagnetic driving/receiving unit for a field device of automation technology

1. An electromechanical transducer unit for a field device of automation technology, comprising:

a membrane embodied to execute mechanical oscillations;

two rods, each extending perpendicular to the membrane and secured to the membrane at a proximal end;

a housing, wherein the membrane forms at least one portion of a wall of the housing and wherein the two rods extend into the housing interior;

two magnets, each magnet secured in an end region opposite the membrane to a different one of the two rods at a corresponding distal end; and

a coil with a core, the coil secured adjacent the magnets within the housing opposite the two rods and contactable with an electrical, alternating current signal,

wherein the coil is configured to produce a magnetic field that causes the two rods, via the two magnets, to execute mechanical oscillations perpendicular to the longitudinal axis of the two rods such that the distal ends of two rods oscillate toward and away from each other, and

wherein the two rods are secured to the membrane such that oscillations of the membrane result from the oscillations of the two rods.

2. The electromechanical transducer unit of claim 1 , wherein the magnets are Alnico magnets.

3. The electromechanical transducer unit of claim 1 , wherein the core of the coil is a part of a pot-shaped armature unit having a floor, a peripheral wall and a stub extending centrally from the floor into the interior of the armature unit, wherein the stub forms the core of the coil, and wherein the peripheral wall serves as a magnetic field guide back.

4. The electromechanical transducer unit of claim 3 , wherein the armature unit is composed of a material with relatively high magnetic permeability or of a metallic glass.

5. The electromechanical transducer unit of claim 4 , wherein the material is iron, cobalt or cobalt iron.

6. The electromechanical transducer unit as claimed in claim 3 , wherein the two magnets extend contactlessly into the pot-shaped armature unit and are disposed at the same separation distance from the coil on oppositely lying sides when no magnetic field is present.

7. An apparatus for determining and/or monitoring at least one process variable of a medium in a containment, comprising:

a sensor unit including at least one electromechanical transducer unit, each electromechanical transducer unit including:

a membrane embodied to execute mechanical oscillations;

two rods, each extending perpendicular to the membrane and secured to the membrane at a proximal end;

a housing, wherein the membrane forms at least one portion of a wall of the housing and wherein the two rods extend into the housing interior;

two magnets, each magnet secured in an end region opposite the membrane to a different one of the two rods; and

a coil with a core, the coil secured adjacent the magnets within the housing opposite the two rods and contactable with an electrical, alternating current signal,

wherein the coil is embodied to produce a magnetic field that causes the two rods, via the two magnets, to execute mechanical oscillations perpendicular to the longitudinal axis of the two rods such that the distal ends of two rods oscillate toward and away from each other, and

wherein the two rods are secured to the membrane such that oscillations of the membrane result from the oscillations of the two rods; and

an electronics unit,

wherein the at least one electromechanical transducer unit is embodied to excite the sensor unit to execute mechanical oscillations using an electrical excitation signal in the form a first electrical, alternating current signal supplied to the coil, to receive mechanical oscillations of the sensor unit, and to convert the oscillations of the sensor unit into an electrical, received signal in the form of a second electrical, alternating current signal, and

wherein the electronics unit is embodied to produce the exciter signal starting from the received signal, and to determine the at least one process variable at least based on the received signal.

8. The apparatus of claim 7 , wherein the sensor unit includes an oscillatable unit connected to the at least one electromechanical transducer unit.

9. The apparatus of claim 8 , wherein the oscillatable unit includes at least one portion of the membrane, or at least one portion of the membrane and at least one oscillatory rod secured thereto.

10. The apparatus of claim 8 , wherein the membrane has two portions connected to one another by a force-transmitting connection, wherein a first portion is associated with the electromagnetic transducer unit and a second portion is associated with the oscillatable unit.

11. The apparatus of claim 8 , wherein the oscillatable unit is arranged in a defined position within the containment such that it descends to a determinable immersion depth in the medium.

12. The apparatus of claim 8 , wherein the oscillatable unit is an oscillatory fork with two rods, and wherein the two rods of the electromechanical transducer unit secured to the membrane and the two oscillatory rods secured to the membrane are arranged oppositely lying and mirror symmetrically to one another with reference to a plane perpendicular to a longitudinal axis through the rods and/or oscillatory rods.

13. The apparatus of claim 12 , wherein the two oscillatory rods and the membrane form a first mechanical resonator, the two rods of the electromechanical transducer unit and the membrane form a second mechanical resonator, and the first and second resonators are mechanically coupled with one another via the membrane, and

wherein the frequency of the excitation signal is selected in such a manner that the first and second resonators oscillate in an antisymmetric, oscillatory mode with reference to a plane through the membrane perpendicular to the longitudinal axis of the rods and/or oscillatory rods.

14. The apparatus of claim 13 , wherein the two rods have substantially the same length and/or stiffness, and wherein the length and/or stiffness of the two rods is selected such that an oscillation frequency of the first resonator and an oscillation frequency of the second resonator have essentially the same value when an oscillatable unit of the sensor unit is not covered by the medium.

15. The apparatus of claim 13 , wherein the two rods have substantially the same length and/or stiffness, and wherein the length and/or stiffness of the two rods is selected such that an oscillation frequency of the first resonator and an oscillation frequency of the second resonator have essentially the same value when an oscillatable unit of the sensor unit is covered by a predetermined reference medium.

16. The apparatus of claim 7 , wherein the process variable is a fill level or flow of the medium in the containment, or a density or viscosity of the medium.