Analytical Industries GPR-1500 A Series Trace PPM Oxygen Analyzer - Manual (Page 33)

Advanced Instruments, Inc
33
Sampling
GPR-1500-A Oxygen Transmitter requires a positive pressure to flow the sample gas across the sensor to
measure the oxygen concentration in a sample gas. If a positive pressure sample not available, see
Pressure & Flow section.
Procedure
Following calibration, the transmitter returns to the SAMPLE mode. From the Sample Mode,
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 transmitter. 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 sample input port.
3. 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 1-2 SCHF
is recommended
4. For sample gases under atmospheric or slightly negative pressure, an optional sampling pump is
recommended to push the sample the sensor housing. Generally, when using a pump, no pressure
regulation or flow control device is involved. However, a flow meter upstream of analyzer is
recommended to ensure that the sample flow is adequate.
5. Assure the sample is adequately vented for optimum response and recovery – and safety.
6. Allow the oxygen reading to stabilize for approximately 10 minutes at each sample point.
Note: To avoid erroneous oxygen readings and damage to the sensor, 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).
7. Assure there are no restrictions in the sample or vent lines
8. Avoid drawing a vacuum that exceeds 14” of water column pressure – unless done gradually
9. Avoid excessive flow rates above 5 SCFH which may generate backpressure on the sensor.
10. Avoid sudden releases of backpressure that can severely damage the sensor.
11. Avoid the collection of particulates, liquids or condensation on the sensor that could block the diffusion
of oxygen into the sensor.
Standby
The transmitter has no special storage requirements.
The sensor should remain inside of the sensor housing and connected to the electronics during storage
periods. Before turning the sample gas OFF, ensure that sample/bypass valve (if analyzer equipped) is at
the BYPASS position. This will keep the sensor isolated from ambient air and would be ready to use again
when required with very short down time. If the transmitter is not equipped with a sample bypass and a shut
off valve, allow a very low flow (less than 0.1 SCFH) of a low PPM gas flowing through the sensor. This will
ensure that air would not diffuse into the sensor housing and the sensor will remain purged and ready for a
sample gas analysis.
NOTE: Under isolated conditions, some oxygen will diffuse into the sample system/sensor housing and the
sensor out will slowly climb up but after 2-3 hours, it will reach a Plato, generally less than 400 PPM
Store the transmitter with the power OFF at a safe location and away from a direct heating source.
If storing for an extended period of time, protect the analyzer from dust, heat and moisture.