Advanced Instruments GPR-2800 IS Manual
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Advanced Instruments, Inc25exposure to high O2 concentrations or air is significantly different if a sensor is being installed than if thesensor had been in-service at low oxygen levels for more than 1 week.Sensor Calibration atInstallIn-serviceCalibration% FuelCellAir to 0.1% < 30secondsAir to 0.05% <2minAir to 0.01 < 10minSimilarLess than 5 minThe above times assume the introduction of a zero gas (low level of oxygen in nitrogen) after spancalibration.For optimum accuracy, the O2 concentration of a span gas should be approximate 50-90% of the full scalerange of analysis or one range above the analysis range, e.g. 20.9% O2 on the 0-25% range. Conversely, ifthe recommended span gas is not available and air calibration is not an option, a span gas of the same fullscale range and near the anticipated analysis level (approximately 30-50% of full scale) is acceptable withthe understanding that the accuracy will suffer slightly.Use of span gas near 30% of the full scale range of measurements, at the higher end of the range has theeffect of “expanding the error” as illustrated by Graph A in Example 1 in the Accuracy section above.Prematurely initiating the SPAN CALIBRATION function (before the analyzer reading has stabilized) canresult in erroneous readings as follows:When purging an analyzer to lower ranges and calibrating with a span gas: If the oxygen reading reachesless than 2% of the intended calibration range, enter the value of the span gas. If the oxygen reading isgreater than 2% of the calibration range, add the O2 reading to the value of the span gas (the impact of theoffset on accuracy is minor but the addition allows the oxygen sensor to continue to purge down and avoidnegative readings after calibration.When installing a new oxygen sensor and calibrating with air, allow 2-3 minutes for the sensor to equilibratein ambient air from storage packaging. Failure to do so can introduce error in calibration.Zero CalibrationTypical offset from a %analyzer is less than 0.01%. Therefore, for most applications, a Zero calibration is notrequired. However, ZERO calibration feature has been provided to allow the user to precisely measureoxygen concentration at the very low levels (less than 0.05%). As described below, accomplishing eitherobjective places a degree of responsibility on the user.Determining the true offset requires the user to wait (see Online Recovery Time section) until the analyzerreading is no longer trending downward (best evidenced by a constant horizontal trend on an externalrecording device.The zero offset adjustments is limited to 50% of the most sensitive range of the analyzer. At factory,analyzer is QC tested to confirm that the maximum offset is less than 50% of the most sensitive rangeavailable. Should you observe a zero offset more than 50% of the lowest range, check sample system forany possible leaks, integrity of the zero gas and assure that the analyzer has been given enough time tostabilize on zero gas before initiating the “ZERO CALIBRATION”.Caution: If adequate time is not allowed for the analyzer to establish the true baseline and a ZEROcalibration is performed, the analyzer will in all probability display a negative reading in the sample modeafter a certain period of time. If a negative reading is seen, perform ZERO calibration again. |
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