Generally, rotary angular sensors can be classified into two types ― sensors based on changes in an electric field and a magnetic field, and optical sensors ― according to the physical principle used for measurement. Among them, optical sensors that operate on visible light or infrared light offer advantages of contactless measurement and insensitivity to electric and magnetic fields.
Yu Nam Chol, a researcher at the Science Engineering Institute, has proposed an absolute rotary angular sensor with a nonlinear transparent disc between light source and light dependent resistors (LDR).
In this sensor, the absolute rotary angle is measured by the output resistance of double LDRs which has a linear change by nonlinear transparency of the disc in a range of 0~360° according to the characteristics of LDR’s resistance via irradiance.
This sensor’s advantage is that it is immune to shock and vibration as it has a nonlinear transparent disc instead of a binary coded disc and it has a large gap between the disc and the optical sensor. It means that it is easy to make a sensor. The disc is made of fiber glass and covered up by a self-adhesive tape whose transparency changes nonlinearly in a range of 0~360°.
Another advantage of this sensor is that its resolution is determined by an AD converter in the signal processing circuit as the output signal of LDRs is analogue. Therefore, this rotary angular sensor is provided with a high resolution in a range of 0~360°.
For more information, please refer to his paper “Improving of Characteristics of Rotary Angular Sensor Using Nonlinear Transparent Disc” in “International Journal of Sensors and Sensor Networks”.
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