An infrared sensor uses what type of scanning device to detect a flame?

An infrared sensor is designed to detect flame by identifying the specific wavelengths of light that flames emit, primarily in the infrared spectrum. The lead sulfide cell is particularly effective for this purpose, as it can detect infrared radiation and is sensitive to the thermal radiation produced by flames. This makes it suitable for flame detection applications where infrared radiation is a key factor.

In contrast, the other components play different roles. A photoelectric cell is typically used in applications that respond to visible light, while thermocouples measure temperature rather than detecting specific radiation wavelengths. Photodiodes, while capable of detecting light, are generally more effective in applications involving visible and near-infrared light, rather than the specific infrared signatures associated with flames. Thus, the lead sulfide cell's specific sensitivity to infrared radiation makes it the most appropriate choice for flame detection using an infrared sensor.