Mixes the gas sample with an equal volume of fresh air
Allows use of standard catalytic bead sensor to obtain readings from oxygen deficient atmospheres
As long as O2 concentration in sample exceeds 10%, the combustible gas sensor has enough oxygen to read accurately
Even when atmosphere contains 0 % oxygen, diluting with an equal volume of fresh air produces an O2 concentration of at least 10 % at the combustible sensor
Dilution Fitting Limitations
Amount of combustible gas in the sample is also diluted
Combustible and toxic gas readings must be doubled to obtain true concentrations
That means if a reading of 20 % LEL is obtained while the dilution orifice is being used, the true concentration is actually 40 % LEL!
Dilution Fitting Correction factors
If dilution adapter non-adjustable, may be necessary to calculate correction factor if dilution ratio varies from 50/50
Correction factor is reciprocal of percentage of difference between actual reading and expected value with adapter in place
Example:
When sensor exposed to 50% LEL gas, expected reading with adapter in place is 25% LEL
If actual reading is 20% LEL, the correction factor would be calculated as: 1 / (20% / 25%) = 1.25
Multiplying actual reading by correction factor provides corrected reading with adapter in place: 20% X 1.25 = 25%
Remember, need to double reading (multiply by 2) for true LEL concentration. (20% X 1.25) X 2 = 50% LEL
Dilution Adapter Readings for O2
Many applications require oxygen to be measured at same time as combustible gas readings are obtained from low oxygen environment.
Remove the adapter or block the dilution pore BEFORE taking readings for oxygen
If the adapter is left in place, or the dilution pore is unblocked, the sample will be diluted with fresh air containing 20.9% oxygen
Make sure to allow time for sensor readings to stabilize fully after removing the adapter or blocking the dilution pore BEFORE recording the readings
Thermal Conductivity Sensors
Sensor contains two beads on opposite arms of balanced Wheatstone Bridge circuit
Neither bead receives a catalyst coating
Reference bead isolated from the air being monitored in a sealed chamber, while active bead exposed to atmosphere being sampled
Detection depends on "air conditioning" effect of high concentrations of gas on the active bead
Use of Oxygen Readings to Determine High Range Concentrations of Combustible Gas
At high levels of gas, oxygen concentration drops
Amount of gas inversely proportional to oxygen concentration
Volume percent oxygen used to calculate and display volume percent methane
