Trace Oxygen Analyzer | Appendix | |
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A-4 3000 SERIES ANALYZERS
APPLICATION NOTES ON RESTRICTORS,
PRESSURES, AND FLOW RECOMMENDATIONS
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 as to provide a useable flow rate trough the analyzer. Any line attached to sample vent should be 1/4 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 .2 - 2.4 SLPM . The optimum flow rate is 1 SLPM (mid scale). Note: response time is dependent on flow rate, a low flow rate will result in slow response to O2 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 O2 will be different than optimum value. Higher pressures will produce faster O2 diffusion rates resulting in higher O2 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 recom- mended because as 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 opera- tion at pressures below atmospheric pressure a suffix C ( clamped) cell is required.
RESTRICTION DEVICES:
For proper operation, all 3000 series analyzers require a flow restriction device. This device is typically a restrictor or a valve. This restriction device serves two functions in the sample path. The first function is to limit the flow rate of the sample through the analyzer. A restrictor is chosen to operate over a range of pressures and provide a useable flow rate over that range.
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