Analytical Industries GPR-1535 GB Trace PPM Oxygen Transmitter - Manual (Page 8)

Advanced Instruments Inc.
8
Installation Considerations
Gas Sample Stream: Ensure the gas stream or composition of the controlled atmosphere of the application is consistent with
the specifications and review the application conditions before initiating the installation. Consult the factory if necessary to
ensure the sample is suitable for analysis.
Expected Sensor Life: With reference to the publish specification located as the last page of this manual, the expected life of
all oxygen sensors is predicated on oxygen concentration (< 1000 ppm or air), temperature (77°F/25°C) and pressure (1
atmosphere) in “normal” applications. Deviations are outside the specifications and will affect the life of the sensor. As a rule of
thumb sensor life is inversely proportional to changes in the parameters.
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 or atmosphere must be controlled within the operating temperature parameters in section 4
Specifications. Note: Operating the sensor above the nominal specification of 25⁰C or 77⁰ F has an exponential affect on sensor
life, 2.5% per ⁰C.
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 a controlled atmosphere.
Sample systems and/or flowing gas samples are generally required for applications involving oxygen measurements or
calibration below ambient air to maintain the integrity of the sample. 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.
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 transmitter 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.