| 摘要 |
PURPOSE:To detect correct turbidity with a simple circuitry, by arranging an optical oscillation circuit containing a light receiving element for receiving light from a light emitting element passing through a liquid as light receiving means to detect dirtiness. CONSTITUTION:An LED 10 and an SPD 27 are immersed into a lubricating oil 100 in a facing manner. When an output of an inverter 20 is at the level L at the time t0, an output of an inverter 21 shows the level H and an output of an inverter 22 the level L; voltage at the point (a) lowers exponentially at a time constant determined by a timing capacitor 24 and a timing resistance 25 depending on current flowing through the SPD 27 and the timing resistance 25 from the timing capacitor 24. At the time t1, as the voltage at the point (a) goes down to a threshold voltage VTH of the inverter 20, outputs of the inverters 20-22 are inverted and lower to VTH+VDD. During the period of time t1-t2, photocurrent proportional to the quantity of light received with the SPD 27 flows to the timing capacitor 24 from a diode 26; as the voltage at the point (a) rises to reach VTH at the time t2, the inverters 20-22 invert and the voltage reaches VTH+VDD.
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