Oil End Sensor - Ricoh FT4430 Service Manual

16 April '88

OIL END SENSOR

Oil end detection is based on the difference between the index of refraction of
air and the index of refraction of silicone oil.
The index of refraction of silicone oil (1.40) is very near that of the sensor
so,
casing (1.49);
result, when oil [A] covers the sensor [B], light [C] from the LED [D] is only
refracted slightly at the boundary between the casing and the oil. The
phototransistor [E] stays off.
However, the index of refraction of air is much lower (1 .00). So, the critical
angle for the air-casing interface is much less than that of the oil-casing
interface. Light from the LED strikes the air-casing interface at an angle
greater than the critical angle. So, when oil runs out, light from the LED
reflects instead of refracting and activates the phototransistor.
the oil-casing interface has a very large critical angle. As
2-72
a