Spectrophotometer Dec 12, 2002 Deryck Hong Suryadi Gunawan

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Spectrophotometer Dec 12, 2002 Deryck
HongSuryadi Gunawan
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Presentation Outline

• Project Overview
• Design
• Calibration
• Testing
• Difficulties
• Parts
• Questions

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Project Overview

• Building a measurement tool that is used to
  measure color composition
• Measures light reflected from an object at each
  wavelength.
• Creating a color spectrum and measuring intensity
  of each color.
• Using the intensities to create the color of the
  object and displaying the color on a screen with
  corresponding RGB values.
• The object has to be a piece of single colored
  paper

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Design
Parallel Port
Source
Lens
Diffraction Grating
CCD Sensor
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Design Cont

• The distances between parts have to be
  calculated
• Between Diffraction Grating and the lens
• Between Diffraction Grating and the CCD sensor
• Distance between the lens and the Diffraction
  Grating can be calculated using lens equation
• 1/Object distance 1/Image distance 1/focal
  length

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Design Cont.

• After the Diffraction Grating, the source light
  is diffracted into multiple orders.
• Order 0 (m0) contains the original light. The
  colors of the light in other orders are
  separated. The first order (m1) is used for the
  project

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Color Spectrum

• This project uses the wavelengths from 435 nm to
  740 nm.

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Design Cont.

• Need to Calculate the distance between the
  Diffraction Grating and the CCD sensor(D).
• Since the Diffraction Grating has 1000 lines per
  mm, then d is calculated to be 1um.

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Design Cont.

• The angle for the wavelength( )at 435 nm can
  be found using equation
• is found to be 25.78 degrees.
• The angle for the wavelength( )at 740 nm can
  be found using equation
• is found to be 47.73 degrees.

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Design Cont.

• After finding the angles, the distance (D) can be
  calculated using the following equations
• and are the displacements from the
  central maxima to the maxima of blue and red
  lights. The difference of those two
  displacements has to be the height of the CCD
  sensor.
• The height of the CCD sensor 2048 14um
  2.867cm
• Then D is found to be 2.867cm/0.6172 4.65 cm

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Design Cont.

• Python will be used to create the GUI
• Communication between PC and the CCD sensor
  through parallel port

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Calibration

• The reflected light contains the spectrums of
  light source and the object.
• The spectrum of the light source needs to be
  removed from the spectrum of the reflected light
  to obtain the correct spectrum of the object.
• Using color filters( Red, Green, and Blue) to
  find the pixel locations that capture the
  corresponding color intensity.

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Testing

• Use light with known wavelength to make sure only
  the expected pixel locations produce readings.
• Use color papers which have known RGB values
  (standard) to test the system.

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Difficulties

• Placing the lens, diffraction grating and the
  sensor.
• Calibration
• Color compensation for monitor viewing

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Parts

• Sensor
• Linear CCD sensor
• EPP interface
• High sensitivity
• Size 4 cm x 5 cm
• 2048 pixels of each 14µm 200µm

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Parts Cont
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Parts Cont.

• Lens
• Multi focal length
• Diffraction grating
• 400nm 700 nm
• 1000 lines per mm
• Angular separation of maxima is 36 degrees
• Light Source
• 40 Watts Halogen light

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Question