Analytical Industries GPR-1200 MS ATEX Portable PPB Oxygen Analyzer - Manual (Page 19)

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Note: Satisfying users that the zero offset is reasonably acceptable for their application can be accomplished much
quicker. Unless the zero gas is contaminated or there is a significant leak in the sample connections, the analyzer
should read less than 10 ppm oxygen within 5 minutes after being placed on zero gas.
The maximum zero calibration adjustment permitted is 60% of the lowest full scale range available, which normally
is 1 ppm. Thus the maximum zero calibration adjustment or zero offset is 0.6 ppm oxygen. Accordingly, the
analyzer’s ZERO has not been adjusted prior to shipment because the factory conditions are different from the
application condition at the user’s installation.
Factory Default Zero:
The software will eliminate any previous span calibration adjustment and display the actual the signal output of the
sensor at a specified oxygen concentration.
For example, assuming a zero gas is introduced, the display will reflect an oxygen reading representing basically
the zero calibration adjustment as described above. This feature allows the user to test the sensor’s signal output
without removing it from the sensor housing.
Span Calibration
Maximum drift from calibration temperature is approximately 0.11% of reading per °C. Analyzer is calibrated at the
factory. However, in order to obtain reliable data, the analyzer must be calibrated at the initial start-up and
periodically thereafter. The maximum calibration interval recommended is approximately 3 months, or as
determined by the user’s application.
Calibration involves adjusting the analyzer electronics to the sensor’s signal output at a given oxygen standard, e.g.
a certified span gas with an oxygen content (balance nitrogen) approximating 80% of the next higher full scale
range above the intended measuring range is recommended for optimum accuracy, see Calibration and Accuracy.
Calibration with ambient or instrument air (20.9% or 209,000 ppm) is recommended when installing a new sensor
or when a certified gas is not available.
Factory Default Span
The software will set the SPAN adjustment based on the average oxygen reading (actually the sensor’s signal
output) at a specified oxygen concentration. For example, when a span gas is introduced, the micro-processor will
display an oxygen reading within +50% of the span gas value. This feature allows the user to test the sensor’s
signal output without removing it from the sensor housing.
Manual Span
The user must ascertain that the oxygen reading (actually the sensor’s signal output) has reached a stable value
within the limits entered below before entering the span adjustment. Failure to do so will result in an error.
Procedure:
This procedure assumes a span gas under positive pressure and is recommended for an analyzer without an
optional sampling pump, which if installed downstream of the sensor should be placed in the OFF position and
disconnected so the vent is not restricted during calibration.
1. Caution: To assure an accurate calibration, the temperature and pressure of the span gas must closely
approximate the sample conditions.
2. For calibration purposes, use of the AUTO SAMPLE mode is recommended. However, the user can select the
full scale MANUAL SAMPLE RANGE for calibration as dictated by the accuracy of the analysis required – for