Image Number 2 for United States Patent #4508501.
A process for the surveillance of jacketed radiant heating tubes and recuperative burners using a detector responding to the oxygen partial pressure in the exhaust gas. At low exhaust gas temperatures down to 200.degree. to 300.degree. C., an abrupt change in the detector output signal occurring due to the transition from over-stoichiometric to under-stoichiometric combustion and vice-versa is detected and is reproduced as an actuating and/or alarm signal. The process can also be used for flame surveillance, for the determination of leaks and cracks in jackets, and for surveillance of the tightness of closed magnetic gas valves.