Correction factors are scaling factors used to calibrate gas detection sensors to specific gases. They allow sensors to be calibrated using inexpensive surrogate gases instead of the target gas. For catalytic LEL sensors, correction factors adjust the sensor reading to compensate for differing sensor responses to different gases. Correction factors are provided for common gases like acetone, ethanol, gasoline, and propane to calibrate LEL sensors accurately for those gases. PID sensors also require correction factors since their response depends on a gas's ionization potential, with factors given for gases like benzene, methylene chloride, and carbon monoxide.

1. Correction Factors LEL & PID Paul Tarter Regional Sales Manager RAE Systems

2. What is a Correction Factor? Correction Factor (CF) is a measure of the sensitivity of the LEL/PID sensor to a specific gas CFs are scaling factors, they do not make a LEL/PID sensor specific to a chemical, they only correct the scale to that chemical. Correction Factors allow PID calibration on cheap, non-toxic “surrogate” gas . Ref: RAE handout TN-106/TN-156

3. Catalytic LEL Sensor Response When a LEL monitor is calibrated to a gas (i.e. methane) it always thinks it is seeing methane. Like a truck that is designed to use a specific size of tire That size tire is calibrated to the speedometer.

4. Catalytic LEL Sensor Response If your monitor calibrated for methane is exposed to gasoline It would be like putting a different size tire on that truck and not adjusting the speedometer. It will still show a speed, but it will not be accurate

5. LEL Correction Factors LEL Correction Factors Acetone 2.2 CF Ethanol 1.7 CF Gasoline 2.1 CF Jet Fuel JP-4,-5,-8 3.4 CF Propane 1.6 CF (RAE Systems TN-156)

6. PID Correction Factors 8 9 10 11 12 13 14 15 8.4 9.24 9.54 9.99 10.1 10.5 10.66 11.32 11.47 12.1 14.01 Benzene MEK IPA Ethylene Acetic Acid Methylene chloride Carbon Tet. Carbon Monoxide Styrene Oxygen Ionization Potential (eV) 11.7 eV Lamp 10.6 eV Lamp Not Ionizable 9.8 eV Lamp

7. CF Example: Toluene Toluene CF with 10.6eV lamp is 0.5 so PID is very sensitive to Toluene If PID reads 100 ppm of isobutylene units in a Toluene atmosphere Then the actual concentration is 50 ppm Toluene units 0.5CF x 100 ppm iso = 50 ppm toluene

9. Question?