Analytical Industries GPR-3500 MO Portable Oxygen Analyzer - Manual (Page 16)

Advanced Instruments Inc.
16
Zero Calibration
In theory, the oxygen sensor produces no signal output when exposed to an oxygen free sample gas. However, the portable oxygen
purity analyzer will generate an oxygen reading when sampling oxygen free sample gas due to:
¾ Contamination or quality of the zero gas
¾ Minor leakage in the sample line connections
¾ Residual oxygen dissolved in the sensor’s electrolyte
¾ Tolerances of the electronic components
As mandated by the FDA, calibration requires the use of certified zero (99.9% nitrogen minimum purity) and span (99.2% oxygen
minimum purity). For optimum accuracy and to take advantage of the portable oxygen purity analyzers’ inherent accuracy of 0.1%,
perform the zero and span calibration before each certification. Otherwise calibrate every eight (8) hours.
Medical grade oxygen:
The FDA requires the use of certified gases for zeroing and calibrating analyzers used in certifying medical grade oxygen. Advanced
Instruments Inc. recommends zeroing and calibrating the analyzer before each certification.
The analyzer zero gas must be a certified cylinder of nitrogen with a minimum purity of 99.9%. Once the analyzer has been zeroed
(described below), calibrate (described below) with a certified cylinder of oxygen with a minimum purity of 99.2%.
Non-medical grade oxygen applications:
In non-medical grade oxygen applications the analyzer does not require zeroing before every calibration. It is recommended the
analyzer be calibrated at least monthly. In most cases nitrogen zero gas of 99% minimum purity and a span gas of 95-100% oxygen
purity is sufficient.
For the reasons above, it is not practical to zero a percent portable oxygen purity analyzer. Finding the true zero offset is not always
necessary particularly in the case of applications requiring higher level oxygen measurements because of the low offset value, normally
< 0.1 ppm, is not material to the accuracy of higher level measurements.
Caution: Prematurely zeroing the analyzer can cause a negative reading in both the ZERO and SAMPLE modes.
Default Zero:
The software will eliminate any previous zero 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.
Recommendation: Initiate the DEFAULT ZERO procedure before performing either a ZERO or SPAN CALIBRATION.
Procedure – Zero Calibration:
Refer to Span Calibration below for the detailed procedure. Differences include the displays illustrated below, substituting a suitable
zero gas for the span gas.
1. Access the MAIN MENU by pressing the MENU key.
2. Advance the reverse shade cursor using the ARROW keys to highlight CALIBRATE.
3. Press the ENTER key to select the highlighted menu option.
4. Advance the reverse shade cursor using the ARROW keys to highlight DEFAULT ZERO, to remove all previous adjustments.
5. Press the ENTER key to select the highlighted menu option.
6. Repeat to select ZERO CALIBRATE.
7. The following displays appear: