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Gas Detection 101Gas Detection 101
Paul TarterPaul Tarter
South Central Regional ManagerSouth Central Regional Manager
RAE SystemsRAE Systems
AgendaAgenda
Wheatstone Bridge LEL SensorWheatstone Bridge LEL Sensor
ElectrochemicalElectrochemical
Photo-ionizationPhoto-ionization
Wheatstone Bridge Catalytic Bead Wheatstone Bridge Catalytic Bead LEL SensorsLEL Sensors
Wheatstone bridge catalytic bead Wheatstone bridge catalytic bead LEL sensorsLEL sensors
Catalytic “Hot Bead” combustible sensorCatalytic “Hot Bead” combustible sensor Detect combustion gas by catalytic oxidationDetect combustion gas by catalytic oxidation When exposed to gas oxidation reaction When exposed to gas oxidation reaction
causesbead to heatcausesbead to heat Requires oxygen to detect gasRequires oxygen to detect gas
Developed by Dr. Oliver Johnson 1926-1927 of Developed by Dr. Oliver Johnson 1926-1927 of Standard Oil Co. of CA ( now Chevron)Standard Oil Co. of CA ( now Chevron)
Virtually EVERY combustible gas monitor today is Virtually EVERY combustible gas monitor today is derived form this designderived form this design
Variously Called “Wheatstone Bridge” or “Catalytic Variously Called “Wheatstone Bridge” or “Catalytic Bead” sensorsBead” sensors
Wheatstone bridge catalytic bead Wheatstone bridge catalytic bead sensor is like an electric stovesensor is like an electric stove
•One element has a catalyst and one doesn’t•Both are turned on low•The element with the catalyst “burns” gas at a lower level and heats up•As this is a combustion process a minimum of 12-16% oxygen is required•The hotter element has more resistance and the Wheatstone Bridge measures the difference in resistance between the two elements
Catalytic LEL Sensor ResponseCatalytic LEL Sensor Response
When a LEL monitor is When a LEL monitor is calibrated to a gas (i.e. calibrated to a gas (i.e. methane) it always methane) it always thinks it is seeing thinks it is seeing methane.methane.
Like a truck that is Like a truck that is designed to use a designed to use a specific size of tirespecific size of tire
That size tire is That size tire is calibrated to the calibrated to the speedometer.speedometer.
Catalytic LEL Sensor ResponseCatalytic LEL Sensor Response
If your monitor If your monitor calibrated for methane calibrated for methane is exposed to gasolineis exposed to gasoline
It would be like putting It would be like putting a different size tire on a different size tire on that truck and not that truck and not adjusting the adjusting the speedometer.speedometer.
It will still show a It will still show a speed, but it will not be speed, but it will not be accurateaccurate
Catalytic LEL ResponseCatalytic LEL Response
LEL sensors are typically calibrated for methane gas.LEL sensors are typically calibrated for methane gas. The LEL of methane is 5%.The LEL of methane is 5%. When the meter reads 100% in a methane environment, When the meter reads 100% in a methane environment,
there is 5% methane by volume in the room.there is 5% methane by volume in the room.
Propane = 1.82Propane = 1.82 Hexane = 2Hexane = 2 Turpentine = 2.9Turpentine = 2.9 Acetone = 2.2Acetone = 2.2 Ammonia = 0.8Ammonia = 0.8 Phosphine = 0.26Phosphine = 0.26
Electrochemical (EC) SensorsElectrochemical (EC) Sensors
EC sensors are available in a variety of gases.EC sensors are available in a variety of gases. OxygenOxygen Carbon monoxideCarbon monoxide Hydrogen sulfideHydrogen sulfide ChlorineChlorine AmmoniaAmmonia Sulfur dioxideSulfur dioxide Hydrogen chlorideHydrogen chloride Hydrogen cyanideHydrogen cyanide Nitrogen dioxideNitrogen dioxide Many othersMany others
Electrochemical (EC) SensorsElectrochemical (EC) Sensors
Most are electrochemical sensors with Most are electrochemical sensors with electrodes (two or more) and chemical electrodes (two or more) and chemical mixture sealed in a sensor housing.mixture sealed in a sensor housing.
The gases pass over the sensor The gases pass over the sensor causing a chemical reaction within the causing a chemical reaction within the sensor.sensor.
Electrical charge is created which Electrical charge is created which causes a readout to be displayed.causes a readout to be displayed.
Photoionization Detectors (PID)Photoionization Detectors (PID)
Can detect a wide variety of gases in small Can detect a wide variety of gases in small amountsamounts
Will not indicate what materials are Will not indicate what materials are presentpresent
Can identify potential areas of concern Can identify potential areas of concern and possible leaks or contaminationand possible leaks or contamination
PID TechnologyPID Technology
Technology uses an ultraviolet (UV) Technology uses an ultraviolet (UV) lamp to ionize any contaminants in the lamp to ionize any contaminants in the air.air.
When contaminant particles become When contaminant particles become ionized, they carry an electrical charge ionized, they carry an electrical charge which can be read.which can be read.
Gas that is sampled must have Gas that is sampled must have ionization potential (IP).ionization potential (IP).
What Does a PID Measure?What Does a PID Measure?
8.4
9.24
9.54
9.99
10.1
10.5
10.66
11.32
11.41
12.1
14.01
0 10.6
Styrene
Benzene
MEK
Vinyl Chloride
IPA
Ethylene
Acetic acid
Methylene Chloride
Carbon tetrachloride
Oxygen
Carbon monoxide
What Does a PID Measure?What Does a PID Measure?
Organics:Organics: AromaticsAromatics
BenzeneBenzene Ethyl benzeneEthyl benzene TolueneToluene Xylene Xylene
Ketones & aldehydesKetones & aldehydes AcetoneAcetone MEKMEK AcetaldehydeAcetaldehyde
Amines & amidesAmines & amides Diethyl amine Diethyl amine
Chlorinated hydrocarbons Chlorinated hydrocarbons Trichloroethylene (TCE)Trichloroethylene (TCE)
Sulfur compoundsSulfur compounds MercaptansMercaptans Carbon disulfideCarbon disulfide
Unsaturated hydrocarbonsUnsaturated hydrocarbons BButadieneutadiene Isobutylene Isobutylene
AlcoholsAlcohols Ethanol Ethanol
Saturated hydrocarbonsSaturated hydrocarbons ButaneButane OctaneOctane
InorganicsInorganics Ammonia Ammonia Arsine Arsine
What PIDs Do Not MeasureWhat PIDs Do Not Measure
RadiationRadiation AirAir
NitrogenNitrogen OxygenOxygen Carbon monoxideCarbon monoxide Water vaporWater vapor
ToxicsToxics Carbon monoxideCarbon monoxide Hydrogen cyanideHydrogen cyanide Sulfur dioxideSulfur dioxide
Natural gasNatural gas Methane Methane Ethane Ethane
AcidsAcids Hydrochloric acidHydrochloric acid Hydrofluoric acidHydrofluoric acid Nitric acidNitric acid
OthersOthers FreonsFreons Ozone Ozone
Questions??Questions??