| 摘要 |
PURPOSE:To enable secure detection by providing a pulse light emitting element and a light receiving element in a case and detecting the AC component of pulses of an output signal. CONSTITUTION:When the light emitting element 5 emits red light to a storage tank 1, the light receiving element 6 in the recessed part 4a of the case 4 detects a considerable quantity of reflected light when the level of granular body is A. When the level is B, on the other hand, a part of the reflected light is reflected and received by the element 6 and when the level is C, a little red light returns. Only an AC component is selected by a capacitor 12 from the output of the element 6 and converted by an absolute value circuit 14 into a DC output after the AC amplification of an amplifier 13. This output is compared by a comparator 15 with a reference value which is adjusted previously through a variable resistance 16 to output an H-level signal when the level is at a position A and an L-level signal when the level is at a position C, thus performing the secure detection based upon variation in the signal level. |
