Advanced Instruments Inc.
Handling: Do not use force when using the switches, knobs or other mechanical components. Before moving your
analyzer be sure to disconnect the wiring/power cord and any cables connected to the output terminals of the analyzer.
Sample Pressure and 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 in a control room or an open area around a landfill or bio-pond). The following is applicable
to analyzers equipped with fuel cell type oxygen sensors.
Analyzers designed for in-situ ambient or area monitoring has no real sample inlet and vent. The sensor is exposed
directly to the sample gas and it is intended to operate at atmospheric pressure. The analyzer has a built-in pressure
sensor and the sensor output is automatically compensated for any atmospheric pressure changes.
Inlet Pressure: For the analyzers designed to measure oxygen in a flowing gas stream, the inlet sample pressure
must be regulated between 5-30 psig. Although the rating of the SS tubing and tube fittings/valves itself is considerably
higher (more than 100 psig), a sample pressure of 5-30 psig is recommended for ease of control of sample flow.
The analyzer equipped with a sample system has designated SAMPLE and VENT ports. Connect SAMPLE gas to
SAMPLE and the vent to the VENT ports only.
Caution: If the analyzer is equipped with an optional H2S scrubber, sample inlet pressure must not exceed
30 psig.
Outlet Pressure:In applications where sample pressure is positive, the sample must be vented to an exhaust
pipe at a pressure less than the inlet pressure so that the sample gas can flow through the sensor housing. Ideally, the
sample must be vented to atmospheric pressure.
Note: The sensor may be used at a slight positive pressure (e.g., when sample is vented to a common exhaust where
the pressure might be higher than 1 atmosphere). However, the pressure at the sensor must be maintained at all times
including during the span calibration. This may be accomplished by using a back-pressure regulator at vent line of the
analyzer. Caution: A sudden change in pressure at the sensor may result in the sensor electrolyte leakage.
Flow rates of 1-2 SCFH cause no appreciable change in the oxygen reading. However, flow rates above 5 SCFH may
generate a slight backpressure on the sensor resulting in erroneous oxygen readings.
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 a separate flow control valve and a
flow indicator is used, position flow control valve upstream of the sensor and position a flow indicator downstream of
the sensor. If necessary, a pressure regulator 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 % oxygen measurements, an
optional external sample pump may be used upstream of the sensor to push the sample across the sensor and out to
atmosphere. For PPM 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. However, if the sample pump can
pull/push more than 5 SCFH, a flow control must be used to control the sample flow. The flow control valve must be
positioned in such a way that it does not generate any vacuum on the sensor.
Caution: If the analyzer is equipped with a flow indicator with integral metering valve or a metering flow
control valve upstream of the sensor and the pump is installed downstream of sensor- open the metering
valve completely before turning the pump ON to avoid drawing a vacuum on the sensor and placing an
undue burden on the pump.
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