Correction factors basics
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Correction FactorsCorrection FactorsLEL & PIDLEL & PID
Paul TarterPaul TarterRegional Sales ManagerRegional Sales Manager
RAE SystemsRAE Systems
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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
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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.
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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
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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)
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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
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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
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Question?Question?