Analytical-industries GPR-1900 Series Trace PPB Oxygen Analyzer Manuel d'utilisateur télécharger pdf (Page 10)

Advanced Instruments Inc.

Installation Considerations

Gas Sample Stream: Ensure the gas stream composition of the application is consistent with the specifications and review the

application conditions before initiating the installation. Consult the factory if necessary to ensure the sample is suitable for

analysis.

Note: In natural gas applications such as extraction and transmission, a low voltage current is applied to the pipeline itself to

inhibit corrosion. As a result, electronic devices can be affected unless adequately grounded.

Contaminant Gases: A gas scrubber and flow indicator with integral metering valve are required upstream of the analyzer to

remove interfering gases such as oxides of sulfur and nitrogen or hydrogen sulfide that can produce false readings, reduce the

expected life of the sensor and void the sensor’s warranty if not identified at time of order placement. Installation of a suitable

scrubber is required to remove the contaminant from the sample gas to prevent erroneous analysis readings and damage to the

sensor or optional components. Consult the factory for recommendations concerning the proper selection and installation of

components.

Expected Sensor Life: With reference to the publish specification located as the last page of this manual, the expected life of

all oxygen sensors is predicated on oxygen concentration (< 1000 ppm or air), temperature (77°F/25°C) and pressure (1

atmosphere) in “normal” applications. Deviations are outside the specifications and will affect the life of the sensor. As a rule of

thumb sensor life is inversely proportional to changes in the parameters.

Optimum Accuracy: Determine if Zero Calibration is recommended for your application. If it is Zero Calibration should

precede Span Calibration and both should be repeated after the analyzer has been allowed to stabilize, typically 24-36 hours

after installation. For Span Calibration use 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.

Assuming the initial zero is performed according to the procedure described herein, the analyzer should not require Zero

Calibration again until the either the sensor is replaced or a change is made to the sample system or gas lines, and, it should

not require Span Calibration again for up to 3 months under “normal” application conditions as described in the published

specifications. One of the unique features of analyzers based on the electrochemical galvanic fuel cell type oxygen sensor is the

fact that it can be field calibrated at the user’s discretion to whatever standard of certified span gas the user elects to use.

Zero Calibration: In theory

, the oxygen sensor produces no signal output when exposed to an oxygen free sample gas. In

reality, expect the analyzer to generate an oxygen reading when sampling oxygen free sample gas due to contamination or

quality of the zero gas; minor leakage in the sample line connections; residual oxygen dissolved in the sensor’s electrolyte; and,

tolerances of the electronic components.

Zero calibration, see Determining True Zero Offset below, is recommended only

for online analyzers performing continuous

analysis below 5% of the lowest most sensitive range available with a ppm analyzer, e.g. analysis below 0.5 ppm on the 10 ppm

range, or below 0.1% (1000 ppm) with a percent analyzer. Note: Once the zero offset adjustment is made, zero calibration is

not required again until the sample system connections are modified, or, when installing a new oxygen sensor. As a result, zero

calibration is not practical and therefore not recommended for higher ranges or portable analyzers.

Determining True Zero Offset:

Allow the analyzer approximately 24 hours to stabilize with flowing zero gas as evidenced by a

stable reading or horizontal trend on an external recording device. Note: 24 hours is required to assure the sensor has

consumed the oxygen that has dissolved into the electrolyte inside the sensor while exposed to air or percentage levels of

oxygen. For optimum accuracy, utilize as much of the actual sample system as possible.

Span 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.

Recommendation:

Based on the inherent linearity of the galvanic oxygen sensor enables the user to calibrate the 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 – there is no need to recalibrate the analyzer with span gas containing a lower oxygen

concentration. Calibrating either a ppm or percent analyzer with ambient air (with the exception of Oxygen Purity Analyzers

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Analytical-industries GPR-1900 Series Trace PPB Oxygen Analyzer Manuel d'utilisateur Page 10

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