Analytical-industries GPR-2900 Series Oxygen Analyzer Manuel d'utilisateur télécharger pdf (Page 10)

Advanced Instruments Inc.

Air calibrate the analyzer (with the exception of Oxygen Purity Analyzers intended to measure elevated oxygen levels ranging

from 50-100% oxygen) when operating a percent analyzer, installing and replacing a ppm oxygen sensor, to verify the oxygen

content of a certified span gas or when a certified span gas is not available to calibrate a ppm analyzer (immediately following

air calibration reintroduce a gas with a low oxygen concentration to expedite the return to ppm level measurements).

Materials: Assemble the necessary zero, purge and span gases and optional components such as valves, coalescing or

particulate filters, and, pumps as dictated by the application; stainless steel tubing is essential for maintaining the integrity of

the gas stream for ppm and percentage range (above or below ambient air) analysis; hardware for mounting.

Temperature: The sample must be sufficiently cooled before it enters the analyzer and any optional components. A coiled 10

foot length of ¼” stainless steel tubing is sufficient for cooling sample gases as high as 1,800ºF to ambient.

Pressure & Flow: All electrochemical oxygen sensors respond to partial pressure changes in oxygen. The sensors are equally

capable of analyzing the oxygen content of a flowing sample gas stream or monitoring the oxygen concentration in ambient air

(such as a confined space such in a control room or an open area such as a landfill or bio-pond).

Sample systems and/or flowing gas samples are generally required for applications involving oxygen measurements at levels

other than ambient air and when the pressure exceeds ambient. In these situations, the use of stainless steel tubing and fittings

is critical to maintaining the integrity of the gas stream to be sampled and the inlet pressure must always be higher than the

pressure at the outlet vent which is normally at atmospheric pressure. The sensor is exposed to sample gas that must flow or

be drawn through metal tubing via 1/8” compression inlet and vent fittings, a stainless steel sensor housing with an o-ring seal

to prevent the leakage of air and stainless steel tubing.

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 indicator with an integral metering valve upstream of the sensor is recommended as a means of

controlling the flow rate of the sample gas. 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.

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 se

cond 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.

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Analytical-industries GPR-2900 Series Oxygen Analyzer Manuel d'utilisateur Page 10

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