Patent ID: 7405827

Claim:
Apparatus measuring a gas content, which apparatus includes a light transmitter ( 1 ), by means of which coherent light can be sent to the measurement object ( 3 ), a receiver ( 2 ), by means of which light that has passed through the measurement object ( 3 ) can be detected, and optical means ( 4 , 5 , 6 ), by means of which the light intensity of the light transmitter ( 1 ) can be aimed at the receiver ( 2 ), characterized in that the optical means include a lens element ( 4 ), through which both the transmitted and received light is adapted to pass and the optical axis of which is arranged essentially obliquely relative to the longitudinal axis of the measurement object ( 3 ), so that the angles of the normals of the optical boundaries relative to the measuring signal are set obliquely, the lens element ( 4 ) is both a refracting and a reflecting element, and the lens element ( 4 ) separates the measurement object ( 3 ) from the components ( 1 , 2 , 5 ) liable to dirtying and wear.