| 摘要 |
An inexpensive flame detector capable of self checking for internal faults, and comprising a detecting photodiode used for detection of a flame, a checking photodiode used for checking function a light source optically coupled to the checking photodiode, an operational amplifier having a feedback resistor connected between the output terminal and non-inverting input terminal thereof, and a decision circuit for receiving the output signal from the amplifier. The checking photodiode is optically isolated from the detecting photodiode and is connected in series, in one embodiment, and in parallel, in another embodiment, with the detecting photodiode. The light source is switched ON and OFF at regular time intervals. The detecting photodiode is connected to the non-inverting input thermal of the operational amplifier. Alternatively, both photodiodes are connected to the non-inverting input terminal. The decision circuit judges the condition of the flame and the fault condition of the internal components of the flame detector. The detector is simple in structure , having no moving parts; has long life; is inexpensive to manufacture; and is highly reliable.
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