Teledyne 3000TB-XL - Trace oxygen analyzer - Manual (Page 76)

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Appendix Model 3000TB
­XL
Teledyne Analytical Instruments
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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.