What kind of flame detector can be used for pilot flame detection?

A flame rod is an effective device for pilot flame detection because it directly senses the presence of a flame through electrical conductivity. The flame rod operates on the principle of ionization, where the rod conducts electricity when it is within a flame's ionized atmosphere. This makes it particularly suitable for detecting pilot flames, which are typically smaller and less intense than main flames.

In contrast, other options, while useful in different applications, do not perform as specifically or effectively for detecting pilot flames. For example, thermal detectors respond to changes in temperature and could detect significant heat but may not effectively differentiate between flames or detect smaller pilot flames. Photoelectric sensors operate based on light intensity but might not respond accurately to the flickering of a small pilot flame. Ultrasonic detectors are used primarily for detecting gas leaks or changes in sound pressure and are not designed for flame detection. Hence, the flame rod’s specific mechanism and sensitivity to ionized flames make it the most suitable choice for pilot flame detection.