A sensing apparatus measures the disk tilt angle of a swing or tilting disk check valve without requiring penetration of the valve housing through a rotating shaft seal. A hinge pin extension is rotationally coupled to the valve disk, and a mechanical converter converts rotation thereof into translation of a magnet carrier within a non-magnetic extension of the valve housing. An LVDT core magnet is translated by the magnet carrier within the housing extension while surrounded by LVDT sensor coils mounted to the exterior of the housing extension. The LVDT core magnet and sensor coils thereby provide an LVDT output signal that indicates the tip angle of the valve disk. Embodiments include threaded coupling of the hinge pin extension to the magnet carrier, or coupling therebetween by a converter pin fixed to one of them into angled helical slot of a cylinder fixed to the other of them.