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Short course in photoelectric sensors. Part II
Abstract
Part 1 of this article covered the basic operation of photoelectric controls. In this second of two parts, photoelectric control logic is examined. Photoelectric control logic can be divided into two categories. The first consists of devices that 'condition' the signal between the detector and the output device. These are typically logic modules mounted inside the photoelectric control and include timing or counting functions. The second category is output switch control logic wired in series or parallel, providing an output to the load only when the correct combination of controls is energized.
... It is well known that pressure can be converted into displacement using a Bourdon gauge and diaphragm methods [40] Many fibre-optic sensors have been proposed to measure pressure at high resolution using these pnnciples [35,[41][42][43][44][45] Figure 2 26 shows the schematic diagram o f a differential pressure sensor utilising the displacement o f a diaphragm Wang et al [35] claimed a resolution o f 450 Pa over a range from 0-0 8 MPa Libo et al [42] describe a differential pressure sensor based on corrugated pipes and a rotating reflector as shown in figure 2 27 A linear relationship between differential pressure and the logarithm o f the ratio o f the output intensities is claimed The sensor also compensates for intensity variations, fibre bending losses and thermal expansion in the corrugated pipes Figure 2 27 Diagram o f automatically compensated differential pressure sensor [42] Fibre-optic sensors can be integrated with silicon micro-machining [26] to provide mechanical assemblies for sensors based on these principles among others This interesting area has lead to low cost sensors for many instrumentation applications especially in the area of biomedical sensors This is especially true where small size is required m combination with high performance Silicon micromachinmg exploits the optical and mechanical and even the semiconductor properties o f silicon Silicon micromachinmg is based on the techniques for manufacturing integrated circuits The major difference is that while in microelectronics the critical dimensions o f a device may be below 0 25 |im -for sensors the critical dimensions may range from 10-1000 |im [46] Also there is no need for expensive clean rooms -consequently micromechamcal and micro-optical sensors are relatively inexpensive Dorey and Bradley [47] provide an overview o f the development o f these " mechatromc" systems Industrially photoelectnc sensing is the most common application o f fibre-optic sensing to another. To make sure that the sensor isn't triggered falsely it is wise for delay logic to be employed between the light and dark condition or vice versa [54]. ...
This project deals with the design and development of an optoelectronic sensor system and its possible use in online applications There are two different configurations of this sensor a sensor for surface roughness and another for defect detection. In each configuration the mechanical and optical design are almost identical-optical fibres convey light to and from a surface. Light source driving circuits and photodetection circuits were developed for each sensor. Data acquisition and analysis algorithms were developed for each sensor.
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