Apparatus for determining and/or monitoring at least one process variable

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

an oscillatable unit for introduction into the container;

a housing, wherein said oscillatable unit is connected with said housing in such a manner that said oscillatable unit closes said housing terminally, and wherein at least one hollow space is introduced in said oscillatable unit which hollow space is accessible from an inner space formed by said housing;

a driving/receiving unit for exciting said oscillatable unit to execute mechanical oscillations and for receiving the mechanical oscillations and for transducing them into an electrical, received signal; and

a control/evaluation unit for controlling the oscillation excitement and for evaluating the received signal with respect to the process variable, wherein:

said driving/receiving unit is introduced into said at least one hollow space and said at least one hollow space is filled with a potting material in such a manner that said driving/receiving unit is tied positively with a wall of said hollow space via the potting material wherein:

for accommodating said driving/receiving unit, a first hollow space is provided in a root region of said first element near to said base and a second hollow space is provided in a root region of said second element near to said base; and

at least two piezoelectric units in the form of a piezo bimorph are applied on a board and said board is embodied in such a manner and said piezoelectric units are arranged on said board in such a manner that said piezoelectric units are introducible into said hollow spaces.

2. The apparatus as claimed in claim 1 , wherein:

said piezoelectric unit includes a first tablet-shaped piezoelectric element and a second tablet-shaped piezoelectric element, which are connected for force coupling with one another via respective faces to form a contact surface and which are polarized in the direction perpendicular to said contact surface; and

at least the respective faces of said piezoelectric elements facing away from said contact surface are provided with electrodes for supplying an exciter signal and for tapping a received signal.

3. The apparatus as claimed in claim 1 , wherein:

said driving/receiving unit includes at least one piezoelectric unit having a piezoelectric element and a passive element;

said piezoelectric element is contactable with an exciter signal; and said piezoelectric element is connected mechanically with said passive element in such a manner that the supplying of said piezoelectric element with the exciter signal leads to bending deformations of said piezoelectric unit.

4. The apparatus as claimed in claim 1 , wherein:

at least said oscillatable unit is composed of a synthetic material or a composite material of synthetic material and glass fibers, glass pearls, carbon fibers and/or ceramic powder.

5. The apparatus as claimed in claim 1 , wherein:

at least said oscillatable unit is composed of a metal or a metal alloy, a ceramic, a glass or a composite material of ceramic and glass or ceramic and metal.

6. The apparatus as claimed in claim 1 , wherein:

at least for the case, in which said oscillatable unit is composed of an electrically conductive material, at least one covering or coating of an electrically insulating material is applied on said driving/receiving unit.

7. The apparatus as claimed in claim 6 , wherein:

said potting material, with which said hollow space is filled and/or the material, with which said driving/receiving unit is coated, is composed essentially of epoxide resin, of epoxide resin and corundum powder, ceramic powder or sand, or of epoxide resin and glass pearls or glass fibers.

8. The apparatus as claimed in claim 1 , wherein:

the stiffness of said potting material, with which said hollow space is filled, corresponds essentially to the stiffness of the material of said oscillatable unit.

9. The apparatus as claimed in claim 1 , wherein:

said oscillatable unit includes a first rod, or paddle, shaped element and a second rod, or paddle, shaped element, which are connected with one another via a base.

10. The apparatus as claimed in claim 9 , wherein:

said control/evaluation unit supplies said driving/receiving unit with an exciter signal in such a manner that said rod, or paddle, shaped elements execute bending oscillations in opposite directions.

11. The apparatus as claimed in claim 1 , wherein said oscillatable unit is embodied as a rod-shaped, hollow body with an inner mass formed in an interior of said hollow body on a wall of said hollow body; and

said driving/receiving unit is present in a hollow space provided in said inner mass.

12. The apparatus as claimed in claim 11 , wherein:

said inner mass is rod-shaped, and said hollow space with said driving/receiving unit is arranged in such a manner that said inner mass and said hollow body execute bending oscillations in opposite directions.

13. The apparatus as claimed in claim 1 , wherein:

said control/evaluation unit comprises part of a module including electronic components for producing the exciter signal and/or for evaluating the received signal with respect to the measured variable.