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. <EOS>