Electromagnetic flow rate sensor, comprising: - a measuring tube which has a first end on the inlet side and a second end on the outlet side and can be inserted into a pipe in a pressure-tight manner, said measuring tube having -- a non-ferromagnetic support tube serving as an outer cover of the measuring tube, -- a tubular liner made from an insulating material and accommodated in a cavity of the support tube, said liner being designed to conduct a flowing fluid which is insulated from the support tube, and -- an open-pore support body designed to stabilize the liner and incorporated into said liner, - a magnetic circuit arrangement arranged on the measuring tube, designed to generate and guide a magnetic field which induces an electrical field in the flowing fluid, said circuit comprising -- a first coil, -- a second coil, -- a first ferromagnetic coil core magnetically coupled with the coils (21, 22), having at an end a first front face which is curved at least in part, and -- a second ferromagnetic coil core magnetically coupled with the coils (21, 22), having at an end a second front face which is curved at least in part, and - a first electrode and a second electrode for tapping a voltage of the electric field, - wherein a first and a second coil core seat are formed in the support body with a predefinable depth, -- wherein the first coil core is introduced, with a first end-side coil core section starting from the front face, through a first jacket opening of the support tube and into the first coil core seat of the support body in such a way that the first front face rests with positive locking on a first surface of the coil core seat, and -- wherein the second coil core is introduced, with a second end-side coil core section starting from the front face, through a second jacket opening of the support tube and into the second coil core seat of the support body in such a way that the second front face rests with positive locking on a second surface of the coil core seat. - a measuring tube which has a first end on the inlet side and a second end on the outlet side and can be inserted into a pipe in a pressure-tight manner, said measuring tube having -- a non-ferromagnetic support tube serving as an outer cover of the measuring tube, -- a tubular liner made from an insulating material and accommodated in a cavity of the support tube, said liner being designed to conduct a flowing fluid which is insulated from the support tube, and -- an open-pore support body designed to stabilize the liner and incorporated into said liner, -- a non-ferromagnetic support tube serving as an outer cover of the measuring tube, -- a tubular liner made from an insulating material and accommodated in a cavity of the support tube, said liner being designed to conduct a flowing fluid which is insulated from the support tube, and -- an open-pore support body designed to stabilize the liner and incorporated into said liner, - a magnetic circuit arrangement arranged on the measuring tube, designed to generate and guide a magnetic field which induces an electrical field in the flowing fluid, said circuit comprising -- a first coil, -- a second coil, -- a first ferromagnetic coil core magnetically coupled with the coils (21, 22), having at an end a first front face which is curved at least in part, and -- a second ferromagnetic coil core magnetically coupled with the coils (21, 22), having at an end a second front face which is curved at least in part, and -- a first coil, -- a second coil, -- a first ferromagnetic coil core magnetically coupled with the coils (21, 22), having at an end a first front face which is curved at least in part, and -- a second ferromagnetic coil core magnetically coupled with the coils (21, 22), having at an end a second front face which is curved at least in part, and - a first electrode and a second electrode for tapping a voltage of the electric field, - wherein a first and a second coil core seat are formed in the support body with a predefinable depth, -- wherein the first coil core is introduced, with a first end-side coil core section starting from the front face, through a first jacket opening of the support tube and into the first coil core seat of the support body in such a way that the first front face rests with positive locking on a first surface of the coil core seat, and -- wherein the second coil core is introduced, with a second end-side coil core section starting from the front face, through a second jacket opening of the support tube and into the second coil core seat of the support body in such a way that the second front face rests with positive locking on a second surface of the coil core seat. -- wherein the first coil core is introduced, with a first end-side coil core section starting from the front face, through a first jacket opening of the support tube and into the first coil core seat of the support body in such a way that the first front face rests with positive locking on a first surface of the coil core seat, and -- wherein the second coil core is introduced, with a second end-side coil core section starting from the front face, through a second jacket opening of the support tube and into the second coil core seat of the support body in such a way that the second front face rests with positive locking on a second surface of the coil core seat.