A heating value meter for gases has an outer cylindrical mantle with an outer thermostatic heating apparatus and at least one inlet for introduction of air and at least one inlet for introduction of test or calibration gas. The track-supporting roller includes at least one supporting body made of plastic. The cannula 22 has an open distal end 24 and a sharp, beveled circumferential cutting edge 26 formed on the open distal end 24, the circumferential cutting edge 26 being disposed perpendicularly to the flow lumen 14 of the catheter 12. The organic x-ray detector includes an encapsulation cover at least partially encapsulating the layered structure.