Selection Of Emitters And Receivers Engineering Essay

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INTRODUCTION

Tomography is come from Greek language, "tomo" means Section cut and "graph" means the image. It is the field disciplines that are concerned with getting the cross-sectional images of the body. So it can define the process tomography as a process to get on the plane Pictures of an object. Concerns optical tomography with spatially varying identification Optical properties of absorption and scattering of the means by measuring the response the average transmitted light to the near infrared. Optical Absorption occurs when the incident energy light passes through the Mediterranean and is converted into heat causing attenuation. This is because some materials show to selectively absorb specific frequencies of light. Attenuation arises because Article vague provinces beam. Different materials cause different levels of

Attenuation and scattering, and this is the reality that forms the basis of optical

tomography.

Tomography involves taking measurements around the periphery of an object (e.g. process vessel or patient) to determine what is going on inside. The best known techniques CAT scanning in medicine, however process tomography instrumentation is cheaper, faster and more robust.

Industrial Process Tomography involves the use of no intrusive sensors to acquire two- or three-dimensional images of the internal contents of process vessels, reactors, separators or pipelines

The technology may be used for liquid/liquid, solid/ liquid, gas/liquid, gas/solid/liquid systems. The spatial resolution of the imaging method and the sensitivity of the method depend specifically on the electrical properties of the system being measured and upon the dimensions of the process

To take a high resolution image many projection should be taken from many angles by using several sensors.

OPTICAL PROCESS TOMOGRAPHY

Optical tomography is a method of photography. On the menu that the object is estimated from the absorption and scattering coefficients is the subject of the transfer of optical measurement of external borders. The application of different image parameters related to different information.

Optical process tomography is used for many industrial processes.

1) A flow pipe in the monitoring of industrial processes, and estimate the distribution of particle size of blood vessels.

 2) Process tomography widely used in the medical field through the invention of

technicians and enabled doctors to see through the human body for any

abnormally is surgical, and diagnostic decision-making quickly, which

Affected the therapeutic outcome of disease discovered. Some Medical applications are:

Breast cancer detection and classification

  Monitor the content of brain tissue oxygen and infant mortality

  Scanning Facility

3) In mathematical point of view, and image reconstruction in optical tomography is ill ask the inverse problem. In practice, this means that the problem is in this sense, the data can be measured even small errors lead to arbitrarily large errors in the form of instability estimates. Because of these properties, and mathematical models, and calculation methods, equipment and development of optical tomography is a best task.

Process tomography is a need to improve the business dealing with multi-component mixture design process by making the fundamental difference between the boundary

Components in real time using the imaging process Non-invasive sensors.

The widespread need for direct analysis of the internal characteristics of process plants in order to improve the design and operation of equipment has made process tomography a main research activity within the industrial instrumentation. Originated from the Greek words 'tomos' which means slice and 'graph' meaning picture, tomography can be defined as a picture of a slice [1]. In simple terms,tomography is an imaging technique that enables one to determine the contents of a closed system without physically looking inside it. There are different requirements in an industrial environment than there are within a medical one: different regulations regarding for example use of ionising modalities and different speed requirements [2] Technically, Process Tomography can be described as imaging process parameters in space and time. Important flow information such as concentration measurement, velocity, flow rate, flow compositions and others can be obtained without the need to invade the process or object. As a result,cross sectional images of processes generate better online inspection, monitoring and process control - promoting improved yields and more effective utilization of available process capacity. Potentially, tomographic systems may also be an alternative approach in developing and verifying process theories and models, as well as for improving process instrumentation.

The earlier researches done by Ruzairi [3], Sallehuddin [4], Khoo [5] and Hisyamuddin [6] have shown that the optical fibre sensor is applicable in flow visualization (image reconstruction). The acquired concentration profile from the image reconstruction is needed together with the velocity profile to complete the mass flow rate estimation in a pneumatic conveying system. Basically, the principle of measurements in tomography is to obtain all possible combinations of measurements from the sensor system. The higher the measurements obtained from the sensors, the resolution of the system would be better.

By using the parallel projection, previous researches have each faced the problem of obtaining a high resolution of their system. This is because the parallel projection method limits the number of measurements to the number of sensors being used. In his research, Chan [7] has implemented the switch-mode fan beam projection technique to obtain flow visualization using LED as light source but resolution and the number of sensors in his system is limited by the physical size of the LED emitters.

Thus, this research will focus in implementing the multiple fan beam method using optical fibre sensors to increase both the number of sensors and number of measurements in order to obtain a system with high resolution.

Selection of Emitters and Receivers

Emitters and receivers are the main optical sensors that must be carefully chosen to satisfy the characteristics and requirements of the hardware system. According to Chan [7], for a system which implements the switch-mode fan beam projection, the emitter must have a very fast setting time when driven by a pulse current while the receiver must have fast transient characteristic when exposed to the switched light sources. The selection of the sensors is based on the specified requirements such as size of the emitting area, angular spread of the emitted light, reliability, physical size, dynamic response and costs of the light source.

For the emitters, three types of optical devices are being considered and they are the light emitting diode (LED), infrared (IR) and laser diodes. Although the laser diodes have a fast operational speed, the LED is generally user friendly and is certainly more cost effective when compared with laser diodes. Besides that, the output power of the LED is linearly proportional to driving the current while laser diodes have an output power which is proportional to current above the threshold.

Linearity is an important characteristic to light sources in analog applications which is emphasized in the implementation of the OFPT sensors. Based on the comparisons of the LED and laser diodes in terms of linearity, costs and it is found that the LED is a better choice of emitter for this project.

LED CHARACTERISTICS

Basically multi-colour LED lighting device adapted especially to shed light on the stages of performance, and other visual presentations, a group of light emitting diodes (LEDs) based on a flexible base member, which in turn supported by the device housing. The linear actuator is practical for the transfer of members between the base level position in general, and the position of deflected causing the array led to change the direction of optical axes for a large number of lamps in the array to focus the light emitted from the lamps, respectively. The preferred that the bulbs in the three sets of lights. May be connected to the shield is generally cylindrical housing project in the light of the device.

Also for multi-colour LED light source i want to use single linear array of 8 multi-colour LED's. Here these LED's illuminated both constantly and pulse sequential manner at same speed and same intensity. In here for multi-colour lighting fixtures, including a wide range of LED and 8 different colours, a switching device, light emitting diodes and an intermediary between a common potential references. In my project this multi-colour LED's should have minimum of 100Hz pulse rate.

However, there is a weakness in LED to be used as transmitter because the light of LED is visible light with the wavelength in between 380-700 nm and therefore results in the tomography sensor designed is easily getting noise from the surrounding environment light source [8]. Most lights sources that we use daily are white or visible lights such as the incandescent lamp (light bulb) and fluorescent light which have a peak of radiant power at 550 nm that can simply affect the light received by the photo-receivers.

The most suitable part of the spectrum of light which is suitable to be selected as light source for this project is the infrared. Generally, the wavelength of the infrared LED lies in between 700nm to 1100nm, thus potentially can safeguard the tomography sensor from being affected by visible light.

The selected transmitter used is the SFH484-2 GaAIA infrared emitter with its peak wavelength at 880n. The small radiation angle is necessary because the emitting area needed for the infrared to be coupled with the fibre optics is small and narrow.

Meanwhile, the main requirements to choose the photo-receivers is to select a photo-receiver with high sensitivity, fast switching time (taking into account the transient/rise and fall time), cost effective and most compatible with the selected infrared emitter. Phototransistors generally have a slower response than photodiodes [9] and linearity of the phototransistor is over a much narrower range than a photodiode. Rise time of the phototransistor is poor due to the combined capacitance of the B/E and C/E junctions and the lifetimes of the carriers in the depletion region of the junction. Based on the need of a fast response and high sensitivity, the photodiode is selected as the photo-sensor for this hardware system instead of the phototransistor.

Basically, all the photodiode models have a fast switching time of 5ns and they have the same

diameter. Thus, selection is mainly based on the price and also the spectral range. The first model, SFH203P is apparently the cheapest but a main concern is that if has a very wide spectral range from 400nm to 110nm. As stated earlier, the visible light has a range of 380nm to 700nm, thus this photodiode performance might be influenced by the visible light from the environment. The second model, SFH203PFA has a narrow spectral range but the price is too expensive. The most reasonably priced and has the most agreeable spectral range is the SFH213-FA photodiode and this will be selected to match with the infrared transmitter. Besides that, the SFH213-FA has a fast transient timewhich can reduce the signal setting time [10].

High radiance GaAs and GaAlAs LEDs using neutron, gamma ray and X-ray sources. The radiation-induced source of degradation in these devices was determined by also examining both bare, un-pigtailed LEDs and separate samples of the Corning fibers used as pigtails. No transient effects were observed in the un-pigtailed LEDs during either pulsed neutron or X-ray exposure. In contrast, the Corning doped silica fibers exhibited strong transient attenuation following pulsed X-ray bombardment. Permanent neutron damage in these pigtailed LEDs consisted essentially of light output degradation in the LED itself. While this effect was significant, it is important to note that these LEDs have exceptionally good neutron tolerance in that their average light output degrades by only a factor of 1.7 at fluencies near 1 x 10(to the 14th power)n/sq cm. Permanent gamma ray effects due to a Co-60 irradiation of 1 mega red were restricted to a small increase in attenuation in the fibre. The two primary radiation effects were then transient attenuation in the fibre pigtail and permanent neutron-induced degradation of the LED.

http://sales.hamamatsu.com/assets/applications/SSD/led_kled9001e01.pdf

The light emitting diode (LED) is commonly used as an indicator. 

It can show when the power is on, act as a warning indicator, or be part of trendy jewelry etc. 

It needs to be fed from a DC supply, with the anode positive and the cathode negative, as shown in the diagram.

To calculate the value of the series resistor we need to know the diode forward voltage and current and its connections. 

The necessary data can be obtained from a catalogue or data book. 

In our example it is 2 volts and 20mA (0.02 amps). 

The cathode lead is the one nearest a "flat" on the body.

Since the voltage across the diode is 2 volts and the battery voltage is 12 volts, then the voltage across the resistor is 12-2 = 10 volts. 

The diode is in series with the resistor, so the current through then both is the same, 0.02 amps.

We now know the voltage across, and the current through the resistor. 

From Ohm's Law we can now calculate the value of the resistor.

Resistance = Volts divided by Amps = V/I = 10/0.02 =500 ohms.

Since this is not a standard value we can use a 470 or 560 ohm resistor as this application is not critical of values.

http://www.hobbyprojects.com/circuits2.html

One of the advantages of LEDs above conventional light sources is that they can generate a large variety of saturated and unsaturated colors,

especially when three or more colored LEDs are combined into one unit.

However, LEDs suffer from serious problems in color reproduction due

to the intrinsic color variation between LEDs of the same intended color

and the luminance decrease over time. Hence, the perceived colors of

two supposedly identical LED spots might be different, and, the color of

a supposedly uniform light pattern on a wall might be perceived as

non-uniform. In order to create visually appealing light effects with

LEDs, knowledge on the visibility of spatial color differences is essential.

Many applications and industry standards use the study of MacAdam

[1] as a guideline for tolerable color variations. MacAdam showed that

the just noticeable difference (JND) between the colors of two light

spots placed side by side can be presented as an ellipse in the

chromaticity diagram centered on the chromaticity of the reference

light (see Figure 1). All colors within an ellipse are perceived as equal.

COMPONENTS

Chip AT89C52 1

Crystal oscillator 11.0592MHz 1

Capacitors 30pF 2

Capacitors 10µF 1

Resistors 8.2 kΩ 1

Resistors 10K Ω 8

LED SFH401 8

Power source 5Volts 1 (Power source is usually available in labs)

Burner (programmer) of AT89C52 1 (burner is also usually available in labs)

COMPONENTS ANALYSIS

Chip AT89C52

Description

The AT89C52 is a low-power, high-performance CMOS 8-bit microcomputer with 8K bytes of Flash programmable and erasable read only memory (PEROM). The device is manufactured using Atmel's high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 and 80C52 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C52 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many embedded control applications.

Pin Description

VCC Supply voltage.

GND Ground.

Port 0

Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as highimpedance inputs. Port 0 can also be configured to be the multiplexed loworder address/data bus during accesses to external progr am and data memor y . In this mode, P0 has inte rnal pull-ups. Port 0 also receives the code bytes during Flash programm i n g a n d o u t p u t s t h e c o d e b y t e s d u r i n g p r o g r a m verification. External pullups are required during program verification.

Port 1

Port 1 is an 8-bit bi-directional I/O port with internal pullups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current because of the internal pullups.

In addition, P1.0 and P1.1 can be configured to be the timer / counter 2 external count input (P1.0/ T2 ) and the timer/counter 2 trigger input (P1.1/T2EX), respectively, as shown in the following table. Port 1 also receives the low-order address bytes during Flash programming and verification.

Port 2

Port 2 is an 8-bit bi-directional I/O port with internal pullups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current because of the internal pullups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that use 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pullups when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order address bits and some control signals during Flash programming and verification.

Port 3

Port 3 is an 8-bit bi-directional I/O port with internal pullups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current because of the pullups. Port 3 also serves the functions of various special features of the AT89C51, as shown in the following table. Port 3 also receives some control signals for Flash programming and verification.

RST

Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.

ALE/PROG

Address Latch Enable is an output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation, ALE is emitted at a constant rate of 1/6 the osci l la to r f r equency and may be used for ex terna l timing or clocking purposes. Note, however, that one ALE p u l s e i s s k i p pe d d u r i n g e ac h a c c e s s to e x te r n a l da t a memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weak ly pul led high. Se t ting the ALE-disable bi t has no effect if the microcontroller is in external execution mode.

PSEN

Program Store Enable is the read strobe to external program memory. When the AT89C52 is executing code from external program memory , PSEN i s act i vated twice each machi ne cycle, except that two PSEN activations are skipped during each access to external data memory.

EA/VPP

External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. E A s h o u l d b e s t r a p p e d t o VC C f o r i n t e r n a l p r o g r a m executions. This pin also receives the 12-volt programming enable volta g e ( VP P ) d u r i n g F l a s h p r o g r a m m i n g w h e n 1 2 - v o l t programming is selected.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier.

LED SFH401

Features

•Anode marking: Tab at case Bottom

Cathode is electrically connected to the case

• High reliability

Long life

High radiant intensity

• Matches all Si-Photodetectors

• Hermetically sealed package

•SFH 401: Same package as BPX 43, BPY 62

The GaAs infrared emitting diodes SFH401, fabricated in a liquid phase epitaxy process, features high efficiency and emits radiation at a wavelength in the near infrared range. The radiation is activated by DC or pulse operation in forward direction; simultaneous modulation is possible. The cathode is electrically connected to the case. The applications include light-reflecting switches for steady and varying intensity, IR-remote control, Industrial electronics, "measuring and controlling".

Applications

• Photointerrupters

• IR remote control

• Sensor technology

• Light curtains

Relative Spectral Emission

Radiant Intensity

Features

• Compatible with MCS-51™ Products

• 8K Bytes of In-System Reprogrammable Flash Memory

• Endurance: 1,000 Write/Erase Cycles

• Fully Static Operation: 0 Hz to 24 MHz

• Three-level Program Memory Lock

• 256 x 8-bit Internal RAM

• 32 Programmable I/O Lines

• Three 16-bit Timer/Counters

• Eight Interrupt Sources

• Programmable Serial Channel

• Low-power Idle and Power-down Modes

DESIGN

CONSTRUCTION

100 HZ PULSE

PULSED SEQUENTIAL MANNER

Pulse sequence manner is the measurement technique by which an MRI scan is obtained. It contains the hardware instructions RF pulses, gradient pulses, timings necessary to acquire the data in the desired manner. As implemented by most manufacturers, the pulse sequence actually executed during the measurement is defined from parameters directly selected by the operator and variables defined in template files. This allows the operator to create a large number of pulse sequences using a limited number of template files. Some parameter limits of a pulse sequence depend on how the manufacturer has implemented the technique (gradient pulse duration), while other parameters (max gradient amplitude) are determined by limitations of the scanner hardware. One of the more confusing aspects of MRI is the variety of pulse sequences available from the different equipment manufacturers. As a result, comparison of techniques and protocols between manufacturers is often difficult due to differences in sequence implementation.

CONTROL WAVE LENGTH BY ELECTRONIC CIRCUITS

http://caclab.csd.auth.gr/papers/ISCC-05-papadimitriou-miliou.pdf

CONTROL INTENCITY BY ELECTRONIC CIRCUITS

CONTROL PULSE REPETIONS BY ELECTRONIC CIRCUITS

COMPUTER CONTROL

USES OF OPTICAL PROCESS TOMOGRAPHY

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.

ADVANTAGES OF OPTICAL PROCESS TOMOGRAPHY

Diffuse optical tomography (DOT) is a noninvasive imaging technique in which near-infrared light is used to probe the interior of the body for oxygenation and other physiological changes. Applications include brain monitoring, optical mammography, and diagnostic imaging of joints and limbs.

A major challenge in optical imaging of biological tissue is the strong scattering of visible and infrared light by tissue. Unlike x-rays, low-energy photons do not travel through the body in a straight line, but instead propagate in a diffuse manner and thus carry little spatial information about the volume. DOT systems deal with this situation by using an array of detectors to sample as much reflected light as possible over a surface area, and then processing this information with statistical models of photon transport to generate cross-sectional or 3-D images of the tissue. In addition to structural data, these images provide functional information about the tissue, which can be derived from the typical absorption spectra of specific molecular species such as oxy- and deoxyhemoglobin.

DOT systems use various types of measurement methods, including frequency domain measurement, continuous wave measurement, and time-resolved methods such as time-correlated photon counting. Measurements are mostly made at wavelengths between 750 nm and 1000 nm. Typically, detectors placed close to the light source will detect light scattered from tissue just below the surface, while detectors placed further away will detect light from deeper tissue where the signal is very weak. Imaging deeper tissue thus requires detectors with high sensitivity and wide dynamic range. Detectors should also have excellent time or frequency response in order to discriminate between surface scattering and deep-tissue scattering.

Optical coherence tomography (OCT), introduced in 1991 by Dr. James Fujimoto of MIT, is an optical method for capturing high-resolution, in situ images of tissue for both research and clinical applications. Tissue can be imaged to a depth of a few millimetres through the use of a low-coherence light source and an interferometer.

In the original implementation, cross-sections of the inner eye were constructed by scanning point by point across the tissue surface and taking z-axis (depth) measurements at each point. To acquire data on the reflectance of tissue at different depths, the interferometer's reference beam was continuously adjusted with a scanning mirror - a method that is effective, but slow. Newer systems work faster by eliminating this type of mechanical movement. Instead, they exploit the spectral information contained in the reflected light. There are generally two ways to generate such information: with a broadband light source and a diffraction grating to spatially distribute the spectrum across a linear image sensor, or by adopting a tunable laser as the light source to rapidly scan a range of wavelengths. In both cases, depth data is immediately computed by applying a Fourier transform on the acquired spectrum.

Most OCT applications use detectors and light sources at 830 nm (for retinal imaging) or 1300 nm (for other tissue). In detection, sensitivity and dark current are usually not an issue, since there often is a sufficient amount of light. The more important factors are dynamic range, readout speed, and readout noise.

DISADVANTAGES OF OPTICAL PROCESS TOMOGRAPHY

Why parallel?

Parallel processing is one of the techniques available which can reduce the reconstruction time very significantly.

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