Teledyne 6200E - Sulfides Analyzer - Manual (Page 158)

Calibration Procedures Model 6200E Instruction Manual
158 M6200E Rev: A1
7.1.2. 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.
7.1.3. 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.
7.1.4. Permeation Tubes
Teledyne Analytical Instruments 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 SO2 monitoring.