Ametek 241CE II User Manual page 21

From the Filterblock Assembly, the gas passes through a Flow Restrictor and
then through a flame arrestor before entering the Measuring Cell, where the
sample is measured using the chilled-mirror technique. It then leaves the Cell
and passes through another flame arrestor, a pressure regulator, and a 1 PSIG
check valve on its way back to the Filterblock Assembly and then to the Vent
Line, which vents the used sample gas to atmosphere or to an approved low
pressure (<50 PSIG) flare header.
The sample system consists of:
Component
Sample Probe
Sample Line
Check Valve
Filterblock Assembly
Flow Restrictor
Flame Arrestor Fittings
Measuring Cell
Mirror
RTD
Mirror Support
TEC Assembly
PN 903-8797, Rev A
Function
Extends into the process gas line to obtain a representative sample. Contains
an Isolation Valve to isolate the sample system from the process gas line.
Transports the sample gas to the analyzer at a temperature above its dew-
point.
Prevents gas flow reversal in the Filterblock if the sample pressure drops sud-
denly. This will prevent damage to the Membrane Filters.
The Filterblock Assembly contains two (2) Membrane Filters and a coalescing
filter. Each filter stage has its own Flow Restrictor to provide liquid drainage
and a fast loop to the common Vent Line.
Flow restrictors control the flow rate of the sample gas and balance any pres-
sure drops within the sample system and Measuring Cell. Never operate the
analyzer without the Flow Restrictors in place.
One flame arrestor connects the analyzer to a dry "purge" gas supply (typically
N2) via the Cooler Housing.
Two (2) flame arrestors are used on the Measuring Cell for the gas Sample
Inlet and Outlet.
The Measuring Cell contains the mirrors, LEDs, phototransistors, Thermo-
electric Cooler (TEC), resistive temperature device (RTD) used to measure the
sample gas. These and other Cell components include:
The integral element is the mirror, which has two planed surfaces that are
exposed to the sample gas inside the Measuring Cell. One of these surfaces is
a rough, black surface used to detect hydrocarbon condensation. The other is
a polished, reflective surface used to detect water condensation.
The placement of the mirror surfaces at the top of the gas sample chamber al-
lows excess liquid formed on the mirror to fall away from the light paths. This
prevents the build-up of liquids on the mirror surfaces. Any liquid that falls
from the mirror and doesn't vaporize upon contacting the warmer Measur-
ing Cell wall is swept from the Measuring Cell during the Purging/Hold Stage
through the sample outlet located at the bottom of the Measuring Cell.
Located within the mirror, near the two planed surfaces, is a resistance tem-
perature device (RTD) which is used by the Microcontroller board to monitor
and control mirror temperature.
The mirror is mounted in a plastic support plate that has good mechanical
strength for containing the pressurized sample gas and has poor thermal
conductivity for thermally isolating the mirror.
The lower surface of the Thermoelectric Cooler (TEC) Assembly is in close
thermal contact with the upper surface of the mirror. The upper surface of
the Cooler Assembly is in close thermal contact with the lower surface of the
Heatsink.
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