Analytical Industries GPR-1900 Series Trace PPB Oxygen Analyzer - Manual (Page 9)

Advanced Instruments Inc.
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Note 4: Calibrating with a span gas approximating 10% of the full scale range near the expected oxygen concentration of the
sample gas is acceptable but less accurate than ‘optimum calibration accuracy’ method recommended – the method usually
depends on the gas available. Calibrating at the same 10% of the full scale range for measurements at the higher end of the
range results in magnification of errors as discussed in Graph A and Example 1 and is not recommended. Of course the user can
always elect at his discretion to accept an accuracy error of +2-3% of full scale range if no other span gas is available.
Air Calibration: Based on the inherent linearity of the electrochemical galvanic fuel cell type oxygen sensor enables the user to
calibrate the analyzer with ambient air (20.9% oxygen) and operate the analyzer within the stated accuracy spec on the lowest
most sensitive range available with the analyzer – there is no need to recalibrate the analyzer with span gas containing a lower
oxygen concentration. Except for Oxygen Purity Analyzers intended to measure elevated oxygen levels ranging from 50-100%
oxygen, calibrating either a ppm or percent analyzer with ambient air on the CAL or 0-25% range meets the 80% criteria
discussed in Recommedation 2.
Recommendation 3: Air calibrate the analyzer (with the exception of Oxygen Purity Analyzers intended to measure elevated
oxygen levels ranging from 50-100% oxygen) when operating a percent analyzer, installing and replacing a ppm oxygen sensor,
to verify the oxygen content of a certified span gas or when a certified span gas is not available to calibrate a ppm analyzer
(immediately following air calibration reintroduce a gas with a low oxygen concentration to expedite the return to ppm level
measurements as per Note 3).