| 摘要 |
PROBLEM TO BE SOLVED: To detect the level of interface of the liquid layer comprising two separate, upper and lower, layers. SOLUTION: A first light-emitting device 51 which emits a reference light comprising such wavelength as not absorbed in both water 3 and oil 2, and a second light-emitting device 52 which emits the measurement light comprising such wavelength as absorbed only in the water 3 are provided side by side, and the two lights are alternately irradiated on the liquid in a vessel 1. The light passing the liquid is alternately received with a photo-detector 6, a differential signal is taken as a DC voltage with a rectification/smoothing circuit 8, and a comparator 9 compares its value with a threshold value. When an interface 4 rises above an interface detection position (measurement light irradiation position), only the measurement light is absorbed in the water 3 to reduce a photo-detection intensity. As a result, the differential signal is higher to exceed the threshold value, inverting the output of the comparator 9. Thus, the position of interface is detected with a simple configuration in non-contact manner. |
