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Trace Oxygen Analyzer Maintenance
Teledyne Analytical Instruments 57
A.5 Application Notes
3000 SERIES ANALYZERS
APPLICATION NOTES ON RESTRICTORS,
PRESSURES, AND FLOW RECOMMENDATIONS
The 3000 series analyzers require reasonably regulated sample
pressures. While the 3000 analyzers are not sensitive to variations of
incoming pressure (provided they are properly vented to atmospheric
pressure) the pressure must be maintained to provide a useable flow rate
through the analyzer. Any line attached to sample vent should be ¼” or
larger in diameter.
FLOW RATE RECOMMENDATIONS:
A usable flow rate for a 3000 series analyzer is one which can be
measured on the flowmeter. This is basically 0.2 - 2.4 SLPM . The
optimum flow rate is 1 SLPM (mid scale). Note that response time is
dependent on flow rate; a low flow rate will result in slow response to
O
2
changes in the sample stream. The span flow rate should be the
approximately same as the sample flow rate.
CELL PRESSURE CONCERNS:
The sensors used in 3000 series analyzers are optimized to function
at atmospheric pressure. At pressures other than atmospheric the
diffusion rate of O
2
will be different than the optimum value. Higher
pressures will produce faster O
2
diffusion rates resulting in higher O
2
reading and shorter cell life. To use a 3000 series analyzer at a cell
pressure other than atmospheric, the analyzer must be calibrated with a
known calibration gas at the new cell pressure to adjust for the different
diffusion rate. Cell pressures below 2/3 atmospheric are not
recommended because they tend to cause excessive internal expansion
which may result in seal failure.
For operation at cell pressures other than atmospheric care must be
taken not to change the sample pressure rapidly or cell damage may
occur. For cell pressures above atmospheric, caution must be exercised
to avoid over pressuring the cell holder. (percent analyzers will require
some type of cell retainer to prevent the cell from being pushed out by
the pressure). For operation at pressures below atmospheric pressure a
suffix C (clamped) cell is required.