Apparatus designed to determine and/or à monitor at least one process variable of a medium, said apparatus comprising a unit capable of vibrating mechanically with a membrane and two fork tines, wherein the two fork tines are mounted on the membrane, wherein the unit capable of vibrating mechanically comes at least partially into contact with the medium, at least a transducer unit, which excites the unit capable of vibrating mechanically to produce mechanical vibrations and which receives mechanical vibrations from the unit capable of vibrating mechanically, and at least a housing in which the transducer unit is located, characterized in that the apparatus comprises a limitation element which is arranged in relation to the unit capable of vibrating mechanically, said apparatus comprising - at least a plate, which is arranged between the two fork tines of the unit capable of vibrating mechanically, and - a pot-like element which has an interior space which is open at least on one side, wherein the interior space of the pot-like element surrounds at least a part of the unit capable of vibrating mechanically, wherein the limitation element is designed and arranged in relation to the unit capable of vibrating mechanically in such a way that it limits or at least reduces the volume available to the medium around the fork tines of the unit capable of vibrating mechanically to a well-defined amount and increases the measurement sensitivity of the apparatus, in that the pot-like element is arranged at a short distance (d) to the fork tines, wherein the distance (d) is selected in such a way that, on the one hand, the fork tines are not prevented from performing their vibrations by the pot-like element and, on the other hand, the mass displaced by the fork tines is notably increased. a unit capable of vibrating mechanically with a membrane and two fork tines, wherein the two fork tines are mounted on the membrane, wherein the unit capable of vibrating mechanically comes at least partially into contact with the medium, at least a transducer unit, which excites the unit capable of vibrating mechanically to produce mechanical vibrations and which receives mechanical vibrations from the unit capable of vibrating mechanically, and at least a housing in which the transducer unit is located, characterized in that the apparatus comprises a limitation element which is arranged in relation to the unit capable of vibrating mechanically, said apparatus comprising - at least a plate, which is arranged between the two fork tines of the unit capable of vibrating mechanically, and - a pot-like element which has an interior space which is open at least on one side, wherein the interior space of the pot-like element surrounds at least a part of the unit capable of vibrating mechanically, - at least a plate, which is arranged between the two fork tines of the unit capable of vibrating mechanically, and - a pot-like element which has an interior space which is open at least on one side, wherein the interior space of the pot-like element surrounds at least a part of the unit capable of vibrating mechanically, wherein the limitation element is designed and arranged in relation to the unit capable of vibrating mechanically in such a way that it limits or at least reduces the volume available to the medium around the fork tines of the unit capable of vibrating mechanically to a well-defined amount and increases the measurement sensitivity of the apparatus, in that the pot-like element is arranged at a short distance (d) to the fork tines, wherein the distance (d) is selected in such a way that, on the one hand, the fork tines are not prevented from performing their vibrations by the pot-like element and, on the other hand, the mass displaced by the fork tines is notably increased.