Analytical Industries GPR-1900 Series Trace PPB Oxygen Analyzer - Manual (Page 30)

Advanced Instruments Inc.
30
Sampling
GPR-1900 Oxygen Analyzer requires positive pressure to flow the sample gas by the sensor to measure the oxygen
concentration in a sample gas. See Sample System and Pressure & Flow at the beginning of Section 5 Operations. To assure
optimal performance: connect gas lines with metal tubing, quality compression type fittings to minimize leaks, follow pressure
and flow recommendations and avoid exposing the sensor to air and high oxygen concentrations for prolonged periods of time
(this does not include the 5 minutes it should take to air calibrate the analyzer once a week).
Note: Prematurely initiating the ZERO CALIBRATION procedure can cause the analyzer to display a negative reading in both
the ZERO and SAMPLE modes. Prematurely initiating the SPAN CALIBRATION procedure can cause erroneously high offsets and
inaccurate readings.
Procedure:
Following calibration the analyzer returns to the SAMPLE mode after 30 seconds.
1. Select the desired sampling mode - auto or if manual, the range that provides maximum resolution – as described above.
2. Use metal tubing to transport the sample gas to the analyzer.
3. The main consideration is to eliminate air leaks which can affect oxygen measurements above or below the 20.9% oxygen
concentration in ambient air - ensure the sample gas tubing connections fit tightly into the 1/8” male NPT to tube adapter,
and, the NPT end is taped and securely tightened into the mating male quick disconnect fittings which mate with the
female fittings on the analyzer
4. Assure there are no restrictions in the sample line.
5. For sample gases under positive pressure the user must provide a means of controlling the inlet pressure between 5-30
psig and the flow of the sample gas between 1-5 SCFH, a flow rate of 2 SCHF is recommended
6. For sample gases under atmospheric or slightly negative pressure an optional sampling pump is recommended to draw the
sample into the analyzer. Generally, no pressure regulation or flow control device is involved.
7. Caution: If the analyzer is equipped with an optional sampling pump and is intended for use in both positive and
atmospheric/slightly negative pressure applications where a flow meter valve is involved – ensure the valve is completely
open when operating the sampling pump. Refer to the Pressure & Flow section above.
8. Assure the sample is adequately vented for optimum response and recovery – and safety.
9. Allow the oxygen reading to stabilize for approximately 10 minutes at each sample point.
To avoid erroneous oxygen readings and damaging the sensor:
¾ Do not place your finger over the vent (it pressurizes the sensor) to test the flow indicator when gas is flowing to the
sensor. Removing your finger (the restriction) generates a vacuum on the sensor and may damage the sensor (voiding the
sensor warranty).
¾ Assure there are no restrictions in the sample or vent lines
¾ Avoid drawing a vacuum that exceeds 14” of water column pressure – unless done gradually
¾ Avoid excessive flow rates above 5 SCFH which generate backpressure on the sensor.
¾ Avoid sudden releases of backpressure that can severely damage the sensor.
¾ Avoid the collection of particulates, liquids or condensation collect on the sensor that could block the diffusion of oxygen
into the sensor.
¾ If the analyzer is equipped with an optional integral sampling pump (positioned downstream of the sensor) and a flow
control metering valve (positioned upstream of the sensor), completely open the flow control metering valve to avoid
drawing a vacuum on the sensor and placing an undue burden on the pump.
Standby
¾ The analyzer has no special storage requirements.
¾ The sensor should remain connected during storage periods.
¾ Store the analyzer with the power OFF.
¾ If storing for an extended period of time protect the analyzer, cable and sensor from dust, heat and moisture.