Analytical-industries GPR-3100 Series Oxygen Purity Analyzer Manuel d'utilisateur télécharger pdf (Page 10)

Advanced Instruments Inc.

5 Operation

GPR-3100 Rev 2/05 3

Sample System:

The GPR-3100 is supplied with stainless steel flow housing, fittings and tubing along with an integral flow

meter to provide optimum percentage range oxygen measurements. As a rule of thumb, the sample must

be properly presented to the sensor to ensure an accurate measurement. For optimum accuracy the

overall performance is enhanced by an temperature controlled heater system that controls the

temperature around the sensor to eliminate drift and daily calibration requirements associated with

competitive analyzers.

Advanced Instruments Inc. offers a full line of sample handling, conditioning and expertise to meet your

application requirements. Contact us at 909-392-6900 or e-mail us at [email protected]

Controlling Pressure & Flow

All electrochemical oxygen sensors respond to partial pressure changes in oxygen. The inlet pressure

must always be higher than the pressure at the outlet vent which is normally at atmospheric pressure.

Despite the fact the oxygen reading is compensated for variations in barometric pressure (at the vent), it

is extremely critical for suppressed range measurements of 90-100% that backpressure be kept to an

absolute minimum. For this reason the analyzer is equipped with 1/8” inlet connections and ¼” vent

connections.

Flow Through Configuration:

The sensor is exposed to sample gas that must flow or be drawn through metal or plastic tubing, see

Application Pressure below, to the analyzer, through the analyzer’s internal sample system that includes

an o-ring sealed stainless steel sensor housing and finally is normally vented to atmosphere.

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. 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 1liter per minute is recommended for optimum performance.

Assure that the vent line is connected to a ¼” or larger tube and is vented to atmosphere, with the

magnification associated with the use of suppressed ranges even the slightest amount of backpressure

will adversely affect the oxygen reading.

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).

Application Pressure - Positive:

A flow indicator with an integral metering valve positioned upstream of the sensor is provided for

controlling the sample flow rate between 1-5 SCFH. If necessary, a pressure regulator (with a metallic

diaphragm is recommended to prevent high oxygen readings resulting from the use of diaphragms of

more permeable materials) upstream of the flow control valve should be used to regulate the pressure.

Application Pressure - Atmospheric or Slightly Negative:

For accurate percentage range measurements, a sample pump is should be positioned downstream of

the sample inlet to draw the sample from the process through the analyzer’s sample system and by the

sensor. A flow indicator with an integral metering valve positioned downstream of the sensor is necessary

to obtain the recommended flow rate between 1-5 SCFH. If pump loading is a consideration, a second

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Analytical-industries GPR-3100 Series Oxygen Purity Analyzer Manuel d'utilisateur Page 10

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