| CPC B05B 12/081 (2013.01) [G01F 23/292 (2013.01); G01F 23/296 (2013.01)] | 17 Claims |

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1. A sprayer comprising a detection unit for determining when a liquid level of the sprayer falls below a specific level, the sprayer comprising:
a container arranged to contain the liquid;
a passage comprising a first light transparent window, a first opening, a second opening and a resonator, wherein when the liquid in the container is passed through the resonator via the first opening, the liquid is emitted as a gas via the second opening; and
a removable detection unit disposed outside of the passage and comprising:
a light source disposed to emit a light through the first light transparent window for illuminating the gas in the passage such that the gas will reflect the emitted light;
an optical sensor disposed to detect a parameter of the reflected light through the first light transparent window; and
a processor coupled to the optical sensor for stopping the resonator from generating the gas when the parameter of the reflected light is below a first threshold corresponding to the specific level;
wherein the passage further comprises a cavity disposed on a bottom surface of the passage in front of the optical sensor of the removable detection unit, wherein when a water vapour is formed by some of the gas in the passage directly contacting the bottom surface, the resultant water vapour will enter the cavity so that the water vapour will not be detected by the optical sensor.
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