Flame sensor
A flame sensor is provided with a focusing member. Ultraviolet light emitted from a light source is reflected by an inner surface of the focusing member to be focused on an electrode of an electrode pair, to increase the sensitivity.
1. A flame sensor comprising:
an electrical discharge tube including
a tube portion having a tube with openings at both ends of the tube,
a plug portion having an ultraviolet light-transparent glass that blocks one of the openings of the tube,
a base portion blocking the other opening of the tube, and
a pair of electrical discharge electrodes being sealed within the electrical discharge tube, which produces electrical discharge by incidence of ultraviolet light from a light source through the plug portion, the electrical discharge electrodes each having a disc-shape; and
a focusing member having reflecting surface for reflecting the ultraviolet light from the light source to focus on the electrical discharge electrodes, wherein
the reflecting surface has either a parabolic shape or a conical shape having a first opening becoming wider towards the light source and a second opening for allowing the ultraviolet light to reach the electrical discharge electrodes which are provided at a focus of the reflecting surface,
the reflecting surface is formed to be more distant from a line towards the light source from the electrical discharge electrodes, the line running through the center of, and being normal to, the respective disc-shaped electrical discharge electrodes, and
the plug portion is provided closer to the second opening than to the first opening of the reflecting surface of the focusing member.