Ametek 241CE II Operator's Manual page 23

From the Filterblock Assembly, the gas passes through a Flow Restric-
tor 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 pres-
sure 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
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
dewpoint.
Prevents gas flow reversal in the Filterblock if the sample pressure
drops suddenly. This will prevent damage to the Membrane Filters.
The Filterblock Assembly contains (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 pressure 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 N ) via the Cooler Housing.
2
Two flame arrestors are used on the Measuring Cell for the gas
Sample Inlet and Outlet.
The Measuring Cell contains the mirrors, LEDs, phototransistors,
Thermoelectric 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 allows 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 Measuring 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
temperature 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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