Light Sensors

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Light Sensors
2
Photodiode
Anode
Cathode

• A semi-conductor device.
• Capable of generating current when exposed to
  visible light.

• Photodiode usually works under a negative bias
  voltage

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Characteristics of Photodiode
10-3
10-4
Photodiode current (A)
10-5
Vbias 0V
10-6
10-7
10-4
10-3
10-2
10-5
Illuminance (Watts/cm2)
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Photodiode Spectral Response
Diode Current for a fixed amount of illuminance
0.6
0.5
0.4
0.3
0.2
0.1
1100
600
300
400
500
1000
700
800
900
Wavelength (nm)
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Photodiode Sensing Circuit
Vbias
I
-
V0
R1
R2
R3
Example R11M? R2900k? R3100k?
V0100I
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Why Is this Circuit Bad?
Vbias
R1
-
V0
R2
R3
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Vacuum Photomultiplier Tube

• Made of a photosensitive layer and a high-gain
  electron multiplier
• Extremely sensitive light sensor
• Converts incident photons into photoelectrons
• Sensitive in the 200nm to 500nm wavelength range

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Light Sensors In Factories

• Reflective sensor
• Thru-beam
• Retro-reflective

Peanuts
Peanuts
Peanuts
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Reading And Homework

• Reading download an article from
  http//www.centrovision.com/tech2.htm
• Handout 5, P255-261
• Homework Study for Exam 2