EN 14792 - Oxides of Nitrogen by Chemiluminescence Flashcards
What is the principle of chemiluminescence?
EN 14792
- Based on reaction of NO with O3
- Reaction leaves NO2 molecules in excited state, emitting light radiation
- Amount of radiation is proportional to amount of NO in sample gas
- Radiation filtered by an optical filter and converted to electric signal by a photomultiplier tube.
BS EN 14792
Should the filter upstream of the sample line be heated?
EN 14792
Yes
EN 14792
What temperature must the gas be conditioned to?
EN 14792
Outlet temperature of ≤ 4°C
EN 14792
What is allowable for the zero check following zero and span gas calibration?
EN 14792
No significant change on the zero reading
EN 14792
What is the allowable deviation on the pre-test zero and span gas line checks?
EN 14792
< 2% of the span gas value
EN 14792
What specification of zero gas is required?
EN 14792
Nitrogen containing insignificant concentration of Nitrogen Oxides
EN 14792
What specification of span gas is required?
EN 14792
NO or NO / NO₂ mix
(Expanded uncertainty ≤ 2%)
EN 14792
What must the concentration of the span gas be for regulatory work?
EN 14792
Approximately at the half hourly ELV or 50 to 90% of the analyser range
EN 14792
What is maximum allowable analyser response time?
EN 14792
200 seconds to reach 90% of the range
EN 14792
What is the maximum allowable sample residence time?
EN 14792
< 60 seconds
EN 14792
What is the allowable lack of fit (linearity) and how often must the analyser be checked for lack of fit?
EN 14792
≤ 2% checked at least once a year
EN 14792
What is the allowable uncertainty at a 95% confidence interval?
EN 14792
± 10% of the daily ELV
EN 14792
How often must a NO₂ loss check be performed?
EN 14792
Every 3 months
EN 14792
What % of the NO₂ must the NOx converter be capable of converting to NO?
EN 14792
≥ 95%
EN 14792
What is a major source of cross interference in chemiluminescence analysers?
EN 14792
Carbon dioxide, particularly in the presence of water vapour due to quenching.
EN 14792