Correction FactorsCorrection FactorsLEL & PIDLEL & PID

Paul TarterPaul TarterRegional Sales ManagerRegional Sales Manager

RAE SystemsRAE Systems

What is a Correction Factor?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

Catalytic LEL Sensor ResponseCatalytic 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.

Catalytic LEL Sensor ResponseCatalytic 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

LEL Correction FactorsLEL 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)

PID Correction FactorsPID Correction Factors

8

9

10

11

12

13

14

15

8.4

9.24 9.549.99 10.1 10.5

10.6611.3211.47

12.1

14.01

Ben

zene

ME

K

IPA

Eth

ylene

Acetic A

cid

Meth

yle

ne

chlo

ride

Carb

on

Te

t.

Carb

on

M

on

ox

ide

Styren

e

Oxy

gen

Ionization Potential

(eV)

11.7 eV Lamp

10.6 eV Lamp

Not Ionizable9.8 eV Lamp

CF Example: TolueneCF 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 ppmiso= 50 ppmtoluene

Question?Question?