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2 Operational Theory2 Operational Theory
2 Operational Theory2 Operational Theory
2 Operational Theory
Model 356WModel 356W
Model 356WModel 356W
Model 356W
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Teledyne Analytical Instruments
lyte is equal to the water vapor pressure in the sample gas. If the humidity
of the sample is too low, water will evaporate from the electrolyte, drying
the cell. If the sample humidity is too high, water will condense out into the
electrolyte, flooding the cell.
The sample is humidified by bubbling it through water in the humidifier
column just before it enters the cell. The humidifier column is in the same
heated compartment as the cell and so is held at the same temperature. The
water in the column, however, is cooled by evaporation into the sample gas.
Thus, the sample gas will normally have a humidity that is too low for
equilibrium with the cell. It is assumed here, of course, that since the cell
component is heated above ambient temperature, the sample gas is less than
saturated at the compartment temperature when it enters the analyzer.
The humidity of the sample is increased to be in equilibrium with the
cell electrolyte by heating the water in the humidifier column. The humidifer
heater is in the base of the column, and the amount of heating is adjusted
with the humidity control that is located on the panel of the control unit.
The amount of heating required depends on the sample flow rate, the
sample humidity, and the specific heat of the sample. The correct adjust-
ment for the operating conditions of any particular installation is obtained by
checking the cell electrolyte level periodically and replenished when neces-
sary according to the instructions in Section 4.2.3:
Cell Installation
.
The humidifier column also contains baffles to stop water from splas-
hing up into the line to the sample cell at high flow rates.
2.3 Flow System2.3 Flow System
2.3 Flow System2.3 Flow System
2.3 Flow System
The analyzer flow system is shown schematically in Figure 2-1. It
includes a needle valve for adjusting the sample flow rate, a flowmeter to
indicate the sample flow required for calibration, the humidifier, the measur-
ing cell, and an automatic level control system for the water in the humidi-
fier.
As can be seen from Figure 2-1, the sample enters the humidifier
column against the pressure of a water column from the base of the humidi-
fier to the water level in the reservoir, which is approximately 4 inches.
This determines the minimum sample pressure at which any sample can flow
through the analyzer. In practice, the sample pressure must be somewhat
greater than this in order to have an adequate flow rate.
The automatic level control in the humidifier column is accomplished
by connecting the sample outflow from the cell to the bottom of the reser-