Abstract
In this paper, a fiber optic displacement sensor with a new reflectivity compensation method is presented. The proposed compensation method is based on two light receiving channels with characteristic displacement sensitivities. The sensitivity characteristic for each channel is achieved by using fibers with different numerical apertures. The ratio of the intensity values of the two receiving channels is a function of the object displacement and fairly independent from the reflectivity of the measured object. The sensor is characterized by a well-defined measurement spot. By use of a focus lens mounted onto the fiber optics probe head, the object displacement range can be extended. The sensor is suitable for measurements with changing object reflectivity and demanding distance ranges.
Highlights
By use of a focus lens mounted onto the fiber optics probe head, the object displacement range can be extended
Fiber optic displacement sensors are known for decades
The sensitivity of the sensor, which is independent from the object surface reflectivity, delivers a measure for the object displacement
Summary
Fiber optic displacement sensors are known for decades. The simplest fiber optical sensor types use a single transmitting fiber for object illumination and a single receiving fiber for receiving the reflected light [1,2]. The practical use of these simple types is limited Because of this limitation, the desire for fiber optic displacement sensors, which deliver a signal fairly independent of the object’s surface reflectivity, in recent years, led to the development of several compensation methods. The sensitivity difference of the receiving channels is achieved by a distinctive geometrical arrangement of the involved optical fibers in the probe head of the sensor [4,5,6,7,8,9,10] For this class of reflectivity compensated sensors, the intensity ratio of the two channels is fairly independent from the object reflectivity and is a measure of the probe displacement. The disadvantages of the geometrical methods are a complex fiber assembly as well as limitations in measurement ranges, in spot sizes and in spot characteristics
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