Advanced Instruments Inc.
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 the atmosphere or into a pipe at atmospheric pressure.
Note: The sensor may be used at a slightly 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 remain constant at
all times including during the span calibration. This may be accomplished by using a back-pressure regulator at the
vent line of the analyzer. Caution: A sudden change in pressure at the sensor may result in the sensor electrolyte
leakage.
Flow rates of 1-5 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:
The GPR-1200P is equipped with
integral sample pump. The pump is capable of pulling sample from atmosphere to a pressure down to 40 inches of
water column. For analyzer without a sample pump, external sample pump may be deployed. However, user must
ensure that by using external pump, the intrinsic safety of the analyzer is not compromised.
Positioning of a Sampling Pump:
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 valve 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.
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.
Moisture & Particulates:
Installation of a suitable coalescing or particulate filter is required to remove
condensation, moisture and/or particulates from the sample gas to prevent erroneous analysis readings and damage to
the sensor or other optional components. Moisture and/or particulates do not necessarily damage the sensor. However,
collection of moisture/particulate on the sensing surface can block or inhibit the diffusion of sample gas into the sensor
resulting in a reduction of sensor signal output – and the appearance of a sensor failure. Consult the factory for
recommendations concerning the proper selection and installation of optional components.
Moisture and/or particulates generally can be removed from the sensor by opening the sensor housing and
either blowing on the sensing surface or gently wiping or brushing the sensing surface with damp cloth.
Caution: Minimize the exposure of PPM sensors to air during this cleaning process. Air calibration followed
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