Critical PID Performance Issues

Critical PID Performance Issues: Effects of Humidity and Contamination

• Condensation and contamination on lamp window and sensor surfaces can create surface conduction paths between sensing and counter electrodes
• Buildup of contamination provides nucleation points for condensation, leading to surface currents
• If present, surface currents cause false readings and / or add significant noise that masks intended measurement (sometimes called "moisture leakage")
• PID designs MAY require periodic cleaning of the lamp and detector to minimize the effects of contaminants and humidity condensation on PID readings

RAE "3D" PID Design

• Benefits:
  • Rapid response and clearing times
• Limitations:
  • Gap between window and electrodes increases "quenching" effect of water vapor on signal
  • Potential for drawing particulate contaminants into sensor
  • More ionic fragments left behind to be adsorbed onto electrodes and window
• Results:
  • Increased sensitivity to water vapor and humidity
  • Must clean lamp more frequently

Ion Science (BW) PID Design

• Benefits:
  • Design includes "fence electrode" to provide mechanical short circuit between sensing and counter electrodes
  • Electrodes housed in replaceable "stack"
  • Diffusion of molecules into and out of glow zone means less ionic fragments or particulates left behind
• Limitations:
  • Slightly slower response
  • Still vulnerable to H2O signal quenching
  • Operation at higher voltage increases vulnerability to EMI / RFI
• Results:
  • Reduced "moisture leakage" response due to humidity
  • Clean lamp less frequently

GfG PID Design

• Benefits:
  • No gap at all between electrodes and window
  • Diffusion of molecules into and out of glow zone means no ionic fragments or particulates left behind
• Limitations:
  • Slightly slower response
• Results:
  • Lower sensitivity to water vapor and humidity
  • Clean lamp less frequently

G460 PID Specifications

Target Gases:	VOCs and other gases with IP less than 10.6eV
Lamp Energy:	10.6eV
G460 PID Ranges	0.1 - 500 ppm (isobutylene) 0.5