How do OPL and transmission affect TDLS readings?

Video FAQ

How do OPL and transmission affect TDLS measurements?

How does a TDLS work?

• Laser emitting light on one side and a detector receiver on the other side
• Molecules absorb light when the frequency of light matches the frequency of the intramolecular bonds
• Light absorbance is related to the concentration of the molecule being measured 

What affects laser transmission? 

1. Proper Alignment
2. Physical barriers
   • i.e particulates, condensation on the window, etc..            

What is Optical Path Length?

• Distance between the laser and detector 
  • Note: Process nozzles are not included in OPL due to their purge

How is TDLS measurement calculated?

• Concentration of molecule / OPL = Average concentration across the process 

What are the benefits of a longer OPL?

1. More molecules being absorbed creating a stronger absorption single
2. Less susceptible to noise
3. Improve accuracy

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