1. Avinash Jadhav
2K13E11
Light Absorption Gas Sensor using
Optical Fiber

2. Contents:
 Concept
 Block diagram
 Theory
 Test and Observations
 Work Pending

3. Concept
 In this experiment the setup will detect the
Methane or Carbon dioxide gas. As there is
a optical fiber, in this setup cladding of
optical fiber will be removed and it will be
left with core, so the gas in the chamber
will acts as a cladding and will generate the
result after absorbing it.

4. Block Diagaram
Light
Source
Gas Chamber
Detector
Circuit

5. Light Source
In Light source, LED
driver circuit is used it
has output current of
38mA and 5V supply.

6. Detector Circuit
 In Detector circuit, Photo
transistor circuit is used a 100K
resistor is used with General
purpose Photo transistor.

7. Theory
 How the setup will work?
As I will be using different types of led to
see which light absorbs the most and the visible
range is around 400nm to 750nm

8. Working Principle
 Principle of this project is when light source is
passed from an optical fiber cable and then
there is a gas chamber where gas (Carbon
dioxide or Methane) will acts as a cladding
material as it will absorb the light and then it
will get pass to detector circuit. After getting
the result we will know what percentage of
light was absorbed by the gas.

9. Colour Wavelength Frequency
Violet 380–450 nm 668–789 THz
Blue 450–495 nm 606–668 THz
Green 495–570 nm 526–606 THz
yellow 570–590 nm 508–526 THz
orange 590–620 nm 484–508 THz
red 620–750 nm 400–484 THz
Absorption Range of different colour

10. Observations: Without Gas Chamber
(1) Reading using Adhesive tape:
Sr.n
o
Colour of Led (5mm led) Volts
1 White Led 4.9
2 Blue led 4.7
3 Red led 0.8
4 Green led 0.09
5 Yellow led 0.18

11. (2) Reading using Metal Connectors
Sr.n
o
Colour of Led (5mm led) Volts
1 White Led 4.88
2 Blue led 4.88
3 Red led 3.62
4 Green led 0.47
5 Yellow led 3.23

12. `(3) For 3mm Led using Metal Connectors
Sr.n
o
Colour of Led (3mm led) Volts
1 Blue led 2.3
2 Red led 3.8
3 Green led 0.76
4 Yellow led 0.76

13. Comparison between Connectors
result and Adhesive tape results
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
White
Led
Blue led Red led Green
led
Yellow
led
Cellotape
Connectors

14. Work Pending
 As I have taken reading in normal
conditions, now I have to take readings
in a chamber, as my chamber is ready, I
just have to make the setup and take the
readings.

15. Reference
 ALTERNATIVE WAVELENGTH FOR LINEARITY
PRESERVATION OF BEER–LAMBERT LAW IN
OZONE CONCENTRATION MEASUREMENT
 A Hybrid Gas Sensor based on Infrared Absorption for
Indoor Air Quality Monitoring
 Absorbance Based Light Emitting Diode Optical
Sensors and Sensing Devices
 Led Driver Circuits
 Optical Fiber Notes

16. Thank you