How do you replace the Aperture on the POM to reduce light from the lamp?

Procedure for reducing the photodiode voltage on a POM by replacing the light aperture with a smaller one on the lamp side of the measurement cell.

Technical Note No. 046

Replacing Aperture on POM to reduce light from lamp

Date: 4 April 2018

Authors: Craig Williford 

Overview:
This tech note describes the procedure for reducing the photodiode voltage on a POM 
by replacing the light aperture with a smaller one on the lamp side of the measurement 
cell.

Tools needed:

• Philips Screwdriver
• 7/64” Hex Ball end screwdriver
• 3/32” Hex Ball end screwdriver
• Exacto knife or similar (optional) 
                                                                                                        
  

Procedure:

1.0 Remove cover

• Using the 7/64” hex ball end screwdriver, remove 4 hex nuts on back of POM.
• Tilt back cover up as shown and unplug lamp.
  
  

2.0 Remove Nafion

Disconnect valve end of Nafion 

• Disconnect cell end of Nafion
  
  

• Disconnect cell exhaust line
  
  
• Pull out coil of Nafion
  
  3.0 Remove Scrubber
•  Disconnect normally open side of valve
  
• Disconnect inlet connection
  
• Disconnect normally closed side of valve
  

Pull out scrubber assembly

4.0 Remove pump connection

• Disconnect tubing from pressure sensor
  
• Disconnect elbow from pump
  
• Pull out tubing
  
  
  5.0 Remove cell mount screws
•  Use Philips head screwdriver to remove two screws holding temperature sensor 
  and voltage regulator to cell
  
• Use 3/32” hex ball screwdriver to remove three bolts holding cell to enclosure
  
  6.0 Remove cell
• Carefully disconnect the photodiode from the pcb
  
• Pull cell out
  
  
  
  7.0 Remove window retaining ring
  
  8.0 Remove aperture (if aperture is in place)
  
  
  
  9.0 Replace new Aperture
  
  
  10.0 Assemble in reverse order