This paper presents the timing advantage of implementing a multiple-fan-beam projection technique using optical fiber sensors for a tomography system. To prepare the sensors to be used for this projection, a collimator is not needed, but optical fiber lens termination is crucial. In this research, the fiber optic lens for transmitters is modeled by experimental methods to transmit light at an emission angle of 30 deg. Due to this small emission angle, a multiprojection technique can be implemented without the light overlapping. A multiple-fan-beam projection technique is here defined as one allowing more than one emitter to project light at the same time using the switch-mode fan-beam method. This method can increase the optical sensor's ability for flow visualization. For the 32 pairs of sensors used, the two-projection technique and four-projection technique were investigated. Sixteen sets of projections formed one frame of light emission for the two-projection technique, and eight sets did so for the four-projection technique. Compared to the conventional single-light projection used in the switch-mode fan-beam method, multiple-light projection can achieve a higher data acquisition rate, thus minimizing data loss and producing a more accurate real-time tomographic image. For four projections the data acquisition rate is 609.76 frames/s.
We investigate the real-time velocity profile for optical tomography using the sensor-to-sensor (STS) and pixel-to-pixel (PTP) methods. Although both methods are similar, the pixel-to-pixel velocity is more accurate than sensor-to-sensor velocity because it measures the pixel velocity within all areas of the pipe and the input signals are from upstream and downstream concentration profiles. The sensor-to-sensor velocity measures only the peripheral velocity of pipe. This velocity method obtains the input signals from the receiver output voltage of upstream and downstream sensors. Problems occur during the nonflow condition because the receiver may have noise, resulting in an incorrect velocity, which is not 0 ms–1. This kind of problem does not happen in the pixel-to-pixel velocity method because all of the noise obtained is filtered by the image reconstruction algorithm used in this project. The velocity profile can easily be created by the pixel-to-pixel velocity method.
This research concentrates on the implementation of 16 pairs of optical sensors in a process tomography system. The working principle is based on the switch and measure principle in electrical capacitance tomography (ECT), but uses fan beam shaped projection from light emitters. The fast settling time of optical sensors and wide coverage of an optical beam forms the interest to be implemented in a tomography system. At the initial stage, modeling has been carried out to predict the output from 16 pairs of optical sensors implemented with the switching principle. The 16 pairs of optical sensors consist of 16 3-mm PIN photodiodes and 16 3-mm LEDs. The idea is applied with the assumption that the emission angle of the source is large enough to illuminate all the receivers and the emission power is uniform along the projection. The linear back projection algorithm is used to predict the result from the modeling. The results for concentration profiles and reconstructed images of the original objects show significant agreement for further research.
We describe the development of a tomographic system by employing low-cost optical sensors. This sensor selection aims at producing a low-cost solution in visualizing a low dense solid particle conveyor system. The final aim of this project is to achieve real-time monitoring of solid particles having low concentration flow when being conveyed in a vertical pneumatic conveyor. The developed tomography system consists of 32 pairs of light-emitting diodes (LEDs) and silicon PIN photodiodes. These sensors are used to monitor the emitted radiation for fluctuations caused by particles interfering with the beam when passing through it. Each sensor output depends on the position of flow regime within the sensing zone. The relationships between the particle distribution and light attenuation effects are investigated by reconstructing the cross-sectional image through computer programming. A data acquisition system is used to digitalize analog signals from the sensor system and is manipulated by a personal computer in real-time mode. The results obtained from this investigation show that low-cost optical sensors are suitable for monitoring low and medium concentration flowing materials.
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