Analytical Industries GPR-3500 MO Portable Oxygen Analyzer - Manual (Page 11)

Advanced Instruments Inc.
11
Span Calibration
Span Calibration involves adjusting the transmitter electronics to the sensor’s signal output at a given oxygen standard. Maximum drift
from calibration temperature is approximately 0.11% of reading per °C. The frequency of calibration varies with the application
conditions, the degree of accuracy required by the application and the quality requirements of the user. However, the interval between
span calibrations should not exceed three (3) months.
Note: Regardless of the oxygen concentration of the standard used, the span calibration process takes approximately 10 minutes,
however, the time required to bring the analyzer back on-line can vary depending on a combination of factors and assume exposure to
a zero/purge/sample gas** with an oxygen content below the stated thresholds immediately after span calibration:
* Refer to analyzer specifications for comparable data on the Pico-Ion UHP and MS oxygen sensors.
Recommendations General:
¾ The interval between span calibrations should not exceed three (3) months.
¾ Initiate the DEFAULT ZERO and DEFAULT SPAN procedures before performing either a ZERO or SPAN CALIBRATION.
¾ Caution: Prematurely initiating the SPAN CALIBRATION function before the analyzer reading has stabilized can result in erroneous
readings. This is especially true when installing a new sensor that must adjust to the difference in oxygen concentrations. It should
take about 2 minutes for the sensor to equilibrate in ambient air from storage packaging.
¾ Always calibrate at the same temperature and pressure of the sample gas stream.
¾ For 'optimum calibration accuracy' calibrate with a span gas approximating 80% of the full scale range one or a higher range than
the full scale range of interest (normal use) to achieve the effect of “narrowing the error” by moving downscale as illustrated by
Graph A in the Accuracy & Calibration section.
¾ Calibrating with a span gas approximating 5-10% 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.
¾ Calibrating at the same 5-10% of the full scale range for measurements at the higher end of the range (example: calibrating an
Oxygen Purity Analyzer in air at 20.9% oxygen with the intention of measuring oxygen levels of 50-100%) results in the effect of
“expanding the error” by moving upscale as illustrated by Graph A and Example 1 in the Accuracy & Calibration section above 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.
Recommendations Air Calibration:
¾ Do not calibrate an analyzer employing the Pico-Ion UHP or MS sensor, or, an oxygen purity sensor with air.
¾ The inherent linearity of the galvanic fuel cell type oxygen sensor enables the user to calibrate any 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 – it is not necessary to recalibrate the analyzer with span gas containing a lower oxygen concentration.
¾ When installing or replacing a ppm or percent oxygen sensor.
¾ To verify the oxygen content of a certified span gas.