Analytical-industries GPR-1600 Series Trace PPB Oxygen Analyzer Manuel d'utilisateur télécharger pdf (Page 7)

Advanced Instruments Inc.

Inlet Pressure: Analyzers designed for flowing samples under positive pressure or pump vacuum (for samples at atmospheric

or slightly negative atmospheres) that does not exceed 14” water column are equipped with bulkhead tube fitting connections

on the side of the unit (unless otherwise indicated, either fitting can serve as inlet or vent) and are intended to operate at

positive pressure regulated to between 5-30 psig although the rating of the fitting itself is considerably higher. Caution: If the

analyzer is equipped with an optional H2S scrubber, inlet pressure must not exceed 30 psig.

Outlet Pressure: In positive pressure applications the vent pressure must be less than the inlet, preferably atmospheric.

Flow Rate: Flow rates of 1-5 SCFH cause no appreciable change in the oxygen reading. However, flow rates above 5 SCFH

generate backpressure and erroneous oxygen readings because the diameter of the integral tubing cannot evacuate the sample

gas at the higher flow rate. The direction the sample gas flows is not important, thus either tube fitting can serve as the inlet or

vent – just not simultaneously.

A flow valve upstream (with flow indicator positioned downstream) of the sensor is recommended as a means of controlling the

flow rate of the sample gas, minimizing air leaks and produce optimum accuracy. A flow rate of 2 SCFH or 1 liter per minute is

recommended for optimum performance.

Caution: 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). To avoid generating a vacuum on the sensor (as described above) during operation, always select and install

the vent fitting first and remove the vent fitting last.

Application Pressure - Positive: A flow indicator with integral metering valve positioned upstream of the sensor is

recommended for controlling the sample flow rate between 1-5 SCFH. To reduce the possibility of leakage for low ppm

measurements, position a metering needle valve upstream of the sensor to control the flow rate and position a flow indicator

downstream of the sensor. If necessary, a pressure regulator (with a metallic diaphragm is recommended for optimum

accuracy, the use of diaphragms of more permeable materials may result in erroneous readings) upstream of the flow control

valve should be used to regulate the inlet pressure between 5-30 psig.

Caution: If the analyzer is equipped with a H2S scrubber as part of an optional sample conditioning system, inlet pressure

must not exceed 30 psig.

Application Pressure - Atmospheric or Slightly Negative: For accurate ppm range oxygen measurements, an optional

external sampling pump should be positioned downstream of the sensor to draw the sample from the process, by the sensor

and out to atmosphere. A flow meter is generally not necessary to obtain the recommended flow rate with most sampling

pumps.

Caution: If the analyzer is equipped with an optional flow indicator with integral metering valve or a metering flow control

valve upstream of the sensor - open the metering valve completely to avoid drawing a vacuum on the sensor and placing an

undue burden on the pump. If pump loading is a consideration, a second throttle valve on the pump’s inlet side may be

necessary to provide a bypass path so the sample flow rate is within the above parameters.

Recommendations 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 (thus 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 liquids or particulates on the sensor, they block the diffusion of oxygen into the sensor

- wipe away.

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.

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Analytical-industries GPR-1600 Series Trace PPB Oxygen Analyzer Manuel d'utilisateur Page 7

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