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Calibration Procedures Teledyne API – T101 Operation Manual
164
6.1.2. 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 H
2
S measuring devices, zero air
should be similar in composition to the sample gas but devoid of H
2
S, hydrocarbons, and
Sulfur dioxide (SO
2
).
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.
6.1.3. GAS STANDARDS
Span gas is specifically mixed to match the chemical composition of the gas being
measured at about 90% of the desired full measurement range. For example, if the
measurement range is 500 ppb, the span gas should have an H
2
S concentration of about
450 ppb.
We strongly recommend that span calibration is carried out with bottled, calibrated H
2
S
or SO
2
span gas, although it is possible to use a permeation tube such as that included in
the IZS valve option. Span gases should be certified to a specific accuracy to ensure
accurate calibration of the analyzer. Typical gas accuracy for calibrated span gases is 1 or
2 %. H
2
S and SO
2
standard gases should be mixed in nitrogen.
6.1.4. PERMEATION TUBES
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 recommend the use of certified H
2
S gases for accurate calibration.
NOTE
Applications requiring US-EPA equivalency do not allow permeation devices to be used as
sources of span gas for calibration of the analyzer where EPA equivalency is required,
such as SO
2
monitoring.
07266B DCN6485