Analytical Industries GPR-1800 IS ATEX Trace PPM Oxygen Transmitter - Manual (Page 8)

Advanced Instruments, Inc
8
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 1-5 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: 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.
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