Analytical Industries GPR-1200 MS ATEX Portable PPB Oxygen Analyzer - Manual (Page 9)

9
Pressure & Flow
All electrochemical oxygen sensors respond to partial pressure changes in oxygen. The inlet pressure must always
be higher than the pressure at the outlet vent which is normally at atmospheric pressure.
The sensor is exposed to sample gas that must flow or be drawn through the analyzer’s internal sample system.
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.
A flow control valve upstream of the sensor controls the flow rate of the sample gas which is displayed by the flow
indicator downstream of the sensor. 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).
Positive Pressure Applications:
If the sample pressure is greater than 30 psig an external pressure regulator (optional) is required upstream of the
analyzer to control of sample flow. A pressure regulator with a metallic diaphragm is recommended to prevent high
oxygen readings that could result from the use of diaphragms constructed of more gas permeable materials.
If other optional sample system components such as coiled metal tubing (samples must be cooled to at least 35-
40º C for continuous use), coalescing filters, scrubbers, etc. are required install the pressure regulator after the
coiled tubing and before the other components and the analyzer. Note: A scrubber requires a flow valve upstream
for optimum efficiency and response time and that the analyzer flow valve is opened completely.
Atmospheric or Slightly Negative Pressure Applications:
For accurate high ppb and/or low ppm range measurements, an optional sample pump is required downstream of
the analyzer to draw the sample through the analyzer. The vacuum drawn on the analyzer and sensor should not
exceed 4” of water.
Caution: Use of pump downstream of the sensor requires the flow control valve upstream of the sensor be
completely opened to avoid drawing excessive vacuum on the sensor, which can damage the sensor.
If pump over-loading (due to the limitation of low flow rate of the sample gas) is a consideration, a second throttle
valve on the pump’s inlet side may be necessary to provide a bypass path, as illustrated below, to prevent the
pump from over-loading and over-heating while maintaining the required sample flow rate within the above-
mentioned parameters.
Standard Bypass Sample System
The GPR-1200MS Portable 0-1 ppm Oxygen Analyzer is equipped with a bypass sample system featured below:
1. Manufacturer supplies the analyzer with the sensor it was qualified with.
2. Isolate the sensor during transport and maintenance intervals and extend sensor life.
3. Isolate the sensor from exposure to high oxygen levels during upset conditions and extend sensor life.
4. Purge the high oxygen levels or air trapped in the sample system following a process upset, changing sample
gas lines or connecting span gas lines.
5. Increase productivity by complimenting the recovery capability of the sensor to reduce downtime.