Patent ID: 8456627

Claim:
A measurement window structure for an optical process measurement device, the measurement window structure comprising: a measurement window made of an optical material and having a measurement surface that is configured for placement into a process solution; a sealing surface for a frame structure of the optical process measurement device for facing the process solution, the measurement window being arranged to press against the sealing surface; and attaching means for pressing the measurement window against the sealing surface to attach the measurement window to the frame structure, the sealing surface being a rotationally symmetrical surface and the surface pressing against the sealing surface being a rotationally symmetrical surface, the surface of the measurement window pressing against the sealing surface being provided with at least one planar surface on the rotationally symmetrical surface through which light will be guided or reflected to the measurement surface, and the sealing surface being at least partly provided with an opening through which light will be guided to the planar surface.