Flange-type liquid-level sensor based on laser light reflection

We report a liquid-level sensor composed of a laser, prism, and photodiode array. The sensor does not require components, such as a sensor head, inside the container that stores liquid. The sensor detects the liquid level based on the difference between the intensities of laser light reflected at the liquid/glass and air/glass interfaces. As the detected liquid level shows a shift from the correct liquid level owing to surface tension and the broadening of the laser light, we correct the shift through calculations. The sensor can be attached to a flange-type glass viewport, providing compatibility with broad-ranging containers for industrial use. The sensor can accurately detect the liquid level with a maximum error of 0.3875 ​mm. We demonstrate the implementation and operation of the liquid-level sensor using a wireless system comprising a sensor head and wireless voltmeter. The reported sensor allows accurate measurement of the liquid level in a tank inside which foreign objects such as sensor heads cannot be installed.