Mohd Rashidi Salim

Incident Angle Approach to Sensitivity Enhancement for Ozone Sensor

The design and mathematical model of a reflective type optical gas sensor is presented. Light source is radiated at an incident angle for 10 cm gas cell with an internal diameter of 0.4 cm. At an incident angle of 1o, optical path length obtained is 342.7886 cm, at 27o incident angle, optical path length is 10.4926 cm and at an incident angle of 28o, optical path length is 9.9631 cm. The model is most efficient at lower incident angles, precisely between (1o and 27o). Effects of variation in diameter and length of gas cell are also demonstrated.

Pressure Dependence of Ozone Absorption Cross Section

Accurate value of absorption cross section is required for correct measurement of ozone concentration. Measurement of ozone has been done at different altitude and pressure. However, previous work has failed to establish significant relation between pressure and ozone absorption cross section. Therefore, this work aims to establish relation between pressure and maximum ozone absorption cross section via spectralcalc.com gas cell simulator. Simulation results show maximum absorption cross section 1.148×10-21 m2 molecule-1 and maximum absorption wavelength 255.442 nm are independent of pressure changes from 0.1 atm to 3.0 atm. Thus, measurement of ozone concentration at maximum absorption wavelength is strongly recommended due to negligible pressure dependence.

Sensitivity and response time of an ozone sensor

The use of optical retro-reflectors in improving the sensitivity and response time of an optical sensor based on optical absorption spectroscopy for the measurement of ozone gas is presented. Two optical retro-reflectors are employed in the design of a 30cm and 20 cm absorption gas cells. Our analysis shows that, in the 30cm gas cell, a sensitivity of 0.0451ppm and 0.0901ppm is achievable while in the 20cm gas cell we can achieve a sensitivity value of 0.0681ppm. However these sensitivity values are dependent on the optical density of the sensor. In general gas cell with wider diameters has potentials for a faster response time.

Investigation of the effect of inlet radius on the response time of a transmission type ozone sensor

The effect of inlet radius of a transmission type optical gas cell on its response time is reported. Six gas cells of varying lengths, and internal radius of 0.32cm were considered at first and then other internal diameters were also investigated afterwards. The effect of inlet radius is easily discernible at all velocities considered; however it is more pronounced at lower flow rates. At a velocity of 16.79cm/s of ozone gas, and for a target sensing time of ≤ 0.5 seconds; we observed that the inlet radius requirements for gas cells of varying lengths and varying internal diameters is not the same for a specific target sensing speed. The length and the internal radius of a gas cell are proportional to its inlet radius.