Analytical Industries GPR-3100 Series Oxygen Purity Analyzer - Manual (Page 27)

Advanced Instruments Inc.
5 Operation
GPR-3100 Rev 2/05 20
consume the oxygen that has dissolved into the electrolyte inside the sensor (while exposed to air or
percentage levels of oxygen).
However, finding the true zero offset (and waiting 24 hours) is not always necessary particularly in the
case of applications requiring higher level oxygen measurements. But, being absolutely precise and
correct requires time.
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 0.1% oxygen within 15 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%. Thus the maximum zero calibration adjustment or zero offset is 0.6% 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.
Accuracy due to manufacturer tolerances may result in a slight difference between the LCD display and
the analog output of the 4-20mA integrated circuit. However, the difference is less than 0.25% of range
and falls well below the specified accuracy of the analyzer.
Default Span:
Refer to Appendix A, 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, when a span gas
of say 21% is introduced, the display will reflect 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.
Default Zero:
Refer to Appendix A, 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
Refer to the Installing Span Gas and Calibration – General Guideline sections above.
Maximum drift from calibration temperature is approximately 0.11% of reading per °C. The GPR-3100
has been calibrated at the factory. However, in order to obtain reliable data, the analyzer must be
calibrated at installation (for optimum accuracy 24 hours after installation) and periodically thereafter
recommended every 3-4 months, or as determined by the user’s application. This involves calibrating the
analyzer electronics to the sensor’s signal output at a given oxygen standard, e.g. instrument air or a
certified span gas approximating 21% oxygen content.
Assuming the initial zero is performed according to the procedure described herein, the analyzer should
not require zeroing again until the either the sensor is replaced or a change is made to the sample
system or gas lines. In most cases, a zero gas of 99% nitrogen purity and a span gas of 95-100%
oxygen purity are sufficient. Following the initial zero and calibration, the analyzer should not require