JPS5952968B2 - flame detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flame detector used in boiler combustion chambers and the like.

This type of flame detector is used for safety confirmation by detecting the presence or absence of a burner flame in a boiler combustion chamber, and conventionally, for example, the one shown in FIG. 1 was used. That is,
A portion of the radiation (including visible light and infrared rays) 91 from the flame 9 of the burner 8 is received at one end 1a of the metal guide tube 1. Since the reflecting mirror 7 is provided at one end 1a, the radiation 91 is reflected along the guide tube 1, and the other end 1a of the guide tube 1 is reflected.
heading to This reflected line 6 travels toward the casing 2 via a transparent sealing member 5 made of glass or the like provided at the other end lb of the guide tube 1. The metal casing 2 includes a light receiving element 3 for receiving the reflected line 6 and converting it into an electric signal, and an amplifier 4 for determining the presence or absence of flame based on the signal from this element 3. A cooling medium such as air is introduced into the guide tube 1 via a conduit 10. The conventional device as described above has the following drawbacks.

(1) Dust, dirt, etc. contained in the cooling medium adhered to the reflecting mirror 7, resulting in changes in detection characteristics, resulting in lack of reliability and maintenance problems. (2) Since the field of view for flame detection is wide, radiation from burners other than the target burner may be received. (3) In systems that detect flame flicker (flicker component) as one means of determining the presence or absence of flame, due to the wide field of view mentioned above, the flicker may be averaged out and sufficient discrimination may not be possible.
SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, to provide a flame detector in which the field of view is reduced without reducing the amount of light, the light receiving direction can be easily changed, and the flame detector is highly reliable. do. In order to achieve this object, the present invention makes radiation based on the flame of a burner enter one end of a guide tube, guides it to a light receiving element through the other end of the guide tube, and converts the radiation into an electrical signal. In the convertible flame detector, the light guide body is housed in a shield tube that extends inside the guide tube from near one end to the other end and extends to the light receiving element; a fixed block that holds the shield tube; and a pin joint that is deflectably connected to the fixed block through a pair of forks, and holds the tip of the light guide body at its internal axis, and the fixed block is coaxially connected to the light guide body. A flame detector characterized in that it is equipped with an optical field limiter having a lens barrel protruding in opposite directions and having a built-in lens system.

Embodiments of the present invention will be described below with reference to the drawings.

Note that the same reference numerals in each drawing indicate similar objects. FIG. 2 shows an embodiment of the flame detector according to the present invention.
The light guide body 20 that penetrates the sealing member 5 of b and extends to the light receiving element 3 is a shield tube 21 for high temperature protection.
It is set up in the.

The light guide body 20 is a so-called fiber scope.
The fiberscope may be one in which incident light propagates based on total internal reflection, or it may be a convergent type in which the incident light propagates using refraction of the fiberscope. At the tip of the light guide body 20, there is an optical field limiter 2 that limits the field of view of the radiation 91 that enters the light guide body 20 of ゛-S.
2 is attached to the guide tube 1 so that it can be deflected within an appropriate angular range from the axial direction of the guide tube 1. The optical field limiter 22 is configured, for example, as shown in detail in FIGS. 3 and 4.

In both figures, a movable block 23 has a pair of forks 24 that slidably engage with a fixed block 27, which will be described later, and is provided with a hole 25 through which the light guide body 20 is inserted. 26 is a lens barrel, and the hole 2 of the movable block 23 is
5, and a convex lens 34 is attached to the tip thereof coaxially with this lens barrel 26.

Reference numeral 27 denotes a fixed block fixed inside the guide tube 1, in which the fork 24 of the movable block 23 is pivotally supported by a support pin 29, and as shown by the two-dot chain line in FIG. It can be deflected within an appropriate angular range from the central direction.

In this embodiment, the guide tube 1 can be deflected in three stages in addition to the axial direction, and the set screw 30 is inserted into the guide hole 31 and fixed at each deflection position. A shield tube 21 is installed in the center hole of the fixed block 27.
The light guide body 20, which is screwed into the shield tube 21 and is individually identified by a locking nut 28, passes through the center hole of the fixed block 27 and is inserted into the movable block 23.
is inserted into the hole 25 and fixed with a perforated screw 32 via a packing 33. The visual field of the radiation 91 incident on the light guide body 20 in the optical field limiter 22 configured as described above as seen from the light guide body 20 is shown in the fifth figure.
As shown in the figure.

In the figure, an optical path 91a indicated by a solid line indicates a radiation line parallel to the optical axis of the lens 34, and after being focused at the focal point F of this lens 34, it enters the tip of the light guide body 20. Next, an optical path 91b indicated by a dotted line indicates a radiation that passes through the periphery of the lens 34 and enters the tip of the light guide body 20. The optical path 91b intersects the optical axis and is diffused again, and at point B the optical path 91b
An optical path 91 that intersects a and expands with distance from then on
It becomes C. Therefore, the range of the radiation incident on the light guide body 20, that is, the field of view seen from the tip of the light guide body is inside the optical path 91C. By appropriately selecting the lens 34, the divergence angle of the optical path 91b, that is, 91C, can be made very small.As a result, the distance to point B can be increased, so that the flame to be measured is located within this distance. Once the detector is installed, the field of view is lens 34.
It will be as small as the area of . Furthermore, even if a flame exists beyond point B, the field of view is small because the divergence angle of the optical path 91C is extremely small. As described above, in the flame detector of the present invention, by the action of the optical field limiter 22, only the radiation based on the flame in a very narrow range of the directed flame is received by the light guide body. The light can be guided to the light receiving element without loss.

Therefore, the following effects can be obtained. (1) Misjudgment caused by receiving radiation from a burner other than the target burner is completely prevented. (2) If the present invention is applied to a system in which flickering of flame is detected as one means of determining the presence or absence of flame, a sufficient discrimination function can be achieved. (3) Compared to the conventional method of providing a pinhole or the like in the light receiving section, the amount of light received is large, so it is easy to convert it into an electrical signal.
(4) Since the radiation is guided by the light guide body, transmission loss is extremely small. (5) Since the lens barrel of the optical field limiter is formed to be deflectable, it is possible to finely adjust the light receiving direction even when the flame detector body is installed, and the radiation rays from a specific part of the flame are optimally received. It can be easily done. (6) The infrared detection method detects changes in flame brightness and extracts high-frequency components, but this method is easy to adopt because the detection field of view is small and the transmission loss of optical signals is extremely small. Note that the optical field limiter 22 may be configured by arranging a convex lens 34 and a concave lens 44 with their respective focal points coincident, as shown in FIG. 6. In this case, the tip of the light guide body 20 The field of view seen from the front can be made extremely narrow as shown in FIG. 5, as shown.

As described in detail above, according to the present invention, it is possible to provide a highly reliable flame detector in which the field of view is reduced without reducing the amount of light, the directionality is good, and the direction of light reception can be adjusted. can.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing a conventional example of a flame detector, Fig. 2 is a system diagram showing an embodiment of a flame detector according to the present invention, and Figs. 3 and 4 are respectively the optical type shown in Fig. 2. FIG. 5 is an explanatory diagram showing the field of view of the optical field limiter shown in FIG. 3, and FIG. 6 is a modification of the optical field limiter shown in FIG. FIG. 3 is an explanatory diagram showing a field of view. 1... Guide tube, 3... Light receiving element, 20
...Light guide body, 21 ... Shield tube, 22 ... Optical field limiter, 23
......Movable block, 24...Fork, 26... Lens barrel, 27... Fixed block, 29... Support pin, 34 ...Convex lens, 44...Concave lens.

Claims (1)

[Claims] 1. A flame detector in which radiation based on the flame of a burner is incident on one end of a guide tube, guided to a light receiving element via the other end of the guide tube, and converted into an electric signal, wherein the inside of the guide tube a light guide body housed in a shield tube that extends from near one end to the other end to the light receiving element; a fixed block that is fixed inside the guide tube and holds the shield tube; and a pair of fixed blocks. It has a lens barrel which is deflectably pin-jointed through a fork, holds the tip of the light guide body at its internal axis, and is coaxially provided with the light guide body and protrudes in the opposite direction to the fixed block, and has a built-in lens system. A flame detector characterized in that it is equipped with an optical field limiter.