Design of industrial furnace endoscopes with high resolution and multiple spectra

In order to solve the existing problems for furnace monitoring, industrial endoscope imaging resolution is low and it is susceptible to dust, which affects the accuracy of temperature measurement. A dual-channel industrial endoscope with multiple spectrum in the visible band (0.48 μm~0.65 μm) and infrared band (3 μm~5 μm and 8 μm~12 μm) was designed and processed. It had a field of view of not less than 100°, a total aperture of less than 60 mm, and a total optical length of more than 1 000 mm. The modulation transfer functions (MTF) of the optical system in the visible band, mid-wave infrared band, and long-wave infrared band are greater than 0.2 at 180 lp/mm, 30 lp/mm, and 12.7 lp/mm, respectively. After passive heat dissipation treatment, the overall optical system was less affected by the thermal difference within the temperature range of 10 ℃ to 70 ℃. The tolerance analysis results show that the designed endoscope has high-resolution imaging quality in the range of 1 m to 5 m object distance, and can distinguish 4 mm line width at 5 m. The designed industrial endoscope has been tested and verified in the factory furnace, which can effectively solve the monitoring problems in the high-temperature and dusty environment of the furnace, and improve the operational safety and production efficiency of industrial furnaces and kilns.