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Calibration Procedures Teledyne API - T100 UV Fluorescence SO2 Analyzer
186
9.1.1.1. ZERO AIR
Zero air is similar in chemical composition to the Earth’s atmosphere but scrubbed of all
components that might affect the analyzer’s readings. For SO
2
measuring devices, zero
air should be similar in composition to the sample gas but devoid of SO
2
and large
amounts of hydrocarbons, nitrogen oxide (NO) and with a water vapor dew point
≤ -15°
C.
Devices such as the API Model 701 zero air generator that condition ambient air by
drying and removal of pollutants are available. We recommend this type of device for
generating zero air.
9.1.1.2. SPAN GAS
Span gas is specifically mixed to match the chemical composition of the gas being
measured at about 80% of the desired full measurement range. For example, if the
measurement range is 500 ppb, the span gas should have an SO
2
concentration of about
400 ppb.
Span gases should be certified to a specific accuracy to ensure accurate calibration of the
analyzer. Typical gas accuracy for SO
2
gases is 1 or 2 %.
If using a secondary dilution source with zero air through a calibrator, then use a
bottle of SO
2
balanced nitrogen.
If calibrator and zero air source are not available, then use a bottle of SO
2
balanced
air.
Teledyne API offers an IZS option operating with permeation devices. The accuracy of
these devices is about ±5%. Whereas this may be sufficient for quick, daily calibration
checks, we strongly recommend using certified SO
2
span gases for accurate calibration.
IMPORTANT
IMPACT ON READINGS OR DATA
Applications requiring US-EPA equivalency do not allow permeation
devices to be used as sources of span gas for calibration of the analyzer.
9.1.1.3. CALIBRATION GAS STANDARDS AND TRACEABILITY
All equipment used to produce calibration gases should be verified against standards of
the National Institute for Standards and Technology (NIST). To ensure NIST
traceability, we recommend acquiring cylinders of working gas that are certified to be
traceable to NIST Standard Reference Materials (SRM). These are available from a variety
of commercial sources.
Table 9-1: NIST-SRM's Available for Traceability of SO
2
Calibration Gases
NIST-SRM
4
TYPE
NOMINAL
CONCENTRATION
1693a
1694a
1661a
Sulfur dioxide in N
2
Sulfur dioxide in N
2
Sulfur dioxide in N
2
50 ppm
100 ppm
500 ppm
06807C DCN6650