Advanced Instruments, Inc.
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 of the two tube fitting connectors can serve as the inlet or vent.
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
1-2 SCFH or 0.4-1 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).
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. If necessary, a pressure regulator (pressure regulator
with a metallic diaphragm is recommended for optimum accuracy, the use 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 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 oxygen measurements, an optional external sampling pump should be positioned upstream
of the sensor to draw the sample from the process and push it through the sensor housing and out to
atmosphere. A flow meter is not necessary if the discharge of the sampling pump approximates the
recommended 1-2 SCFH flow rate.
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.
Delrin Senor Housing with sensor installed.
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