Abstract: A relative pressure measuring instrument has a reference pressure feed that offers a high measure of safety and is easy to produce.

Abstract: The piezoelectric vortex sensing element (3, 3′, 3″, 3+) of this vortex flow sensor (1) can be assembled from individual components in a simple manner; if its piezoelectric element (34, 34′, 34″, 34*, 34+, 34++) should be faulty, it can be easily replaced. Also, the vortex sensing element can be made largely insensitive to vibrations acting from outside. The vortex flow sensor (1) serves to measure the flow velocity and/or the volumetric flow rate of a fluid flowing through a measuring tube (2). A bluff body (4) generating Kármán vortices is disposed along a diameter of the measuring tube and fixed to the measuring tube at at least one fixing point (41). The vortex sensing element responds to vortex-induced pressure fluctuations and either is installed in a wall (22) of the measuring tube down-stream of the bluff body in a tight manner or extends into a main bore (46) extending through the measuring tube into the bluff body.