IR Analyzers Flashcards
What components would be found in an IR absorption analyzer of the single-beam design
1) Chopper
2) Wideband detector
3) Heated filament lamp
4) Salt windows
Which NDIR technique requires you to know the process composition in advance and be aware of all potential interferences?
Positive filtering technique as you need to know what gas to place in the filter cell
What chemical is used in positive-filtering NDIR analyzers to mitigate overlapping absorbance between the CO2 and water?
Isobutane
What is the main advantage of FTIR analysis over the NDIR techniques?
It can quantify every chemical in a substance as it produces a complete absorbance spectrum
How is a TDL superior to the NDIR techniques?
The laser used in a TDL analyzer allows it to have a very narrow band of detection which helps eliminate interferences
Chemiluminescence is a method used to monitor NOx, which includes both NO and NO2. To determine the amount of NO in the sample, the analyzer directly measures __________.
Visible EMR
What is the major difference between the NO mode and NOx mode of the analyzer?
NOx mode has to run through a catalytic converter in order to convert NO2 into NO using a heated metal reactant.
What are common maintenance activities for chemiluminescence analyzer systems?
1) Replace blocked filters
2) Clean blocked capillaries
3) Rebuild or replace the vacuum pump
4) Replace charcoal scrubber
What types of substances can absorb IR radiation?
Substances that have 2 or more covalently bonded heteronuclear atoms
Other than wavelength, what other term is used to specify IR energy?
Wave number (unit/cm)
When a substance absorbs IR energy, what is the effect on the substance?
IR changes the vibration or rotation with the bonds between atoms
What information can be obtained using a DIR analyzer?
Qualitative analysis
List six main components of a DIR analyzer.
1) Continuous multi-wavelength IR source
2) Reference cell with non-IR absorption gas
3) Sample cell containing IR absorbing sample
4) Rotating chopper that selects reference and sample IR beams
5) Monochromator that separates IR wavelengths
6) Non-specific IR detector
What is the significance of dirty sample cell windows in the two different NDIR designs?
Single beam analyzer can compensate for the dirty cell as the reference beam also passes through the sample cell
Dual beam analyzer can not compensate for the dirty cell windows as the reference beam does not pass through the dirty sample cell
What design (component) allows a DIR dual-beam analyzer to use a single IR source? What
is the advantage of this over using 2 sources?
A concave mirror that makes sure the 2 beams are of equal intensity
What is the commercial name for a tightly wound coil of wire that is a common IR source?
Nichrome = Nickel Chromium Alloy
Describe how wide-band detectors differ from differential detectors and what the effect of IR
energy is on each type
Wide-band detectors: respond to any IR source and undergo a change in electrical properties
Differential detectors: respond only to a target gas that is in the cell. Due to the heating effects of IR the cells undergo a pneumatic change
What is the purpose of positive filtering and which NDIR design implements it?
Positive filtering removes interfering IR wavelengths from the sample beam which is used in a dual-beam NDIR design.
What is the purpose of negative filtering and which NDIR design implements it?
Negative filtering reduces effects of ALL interfering IR absorbing gasses and is used in a single-beam design
In negative filtering, what can be found in the reference filter cell and the measurement filter cell?
Reference filter cell: High concentration of IR absorbing target gas
Measurement cell: non-IR absorbing gas
In what filtering technique is the intensity of measurement filter is inversely proportional to sample concentration?
Negative filtering
What must be done to condition extracted samples for analysis by dual beam NDIR analyzers?
1) reduce dew point by removing water vapour
2) Remove particulate matter
Which analyzer configuration is ideally suited for in-situ stack gas analysis and why?
Gas Filter Correlation (GFC-single beam negative filtering) because:
1) They are more sensitive than the double-beam
2) They measure and correct for the background of all IR absorbing interferences in the stack gas
3)They can handle the in situ conditions and do not require a sample cell.
