1-8 | Model 241CE II Hydrocarbon Dewpoint Analyzer
Heatsink Absorbs heat from the Mirror during the Cooling Stage. The heat is
then transferred to the atmosphere through the Heatsink ns. During
the Warming Stage, the Heatsink serves as a passive source of heat
by using the surrounding ambient temperature to heat the mirror.
Optical Systems The Model 241CE II Analyzer employs two Optical Systems in its
Measuring Cell:
• One detects hydrocarbon condensation on the rough, black surface.
• One detects water condensation on the smooth, reective surface.
(This water dewpoint measurement is for internal use only, used for
compensation in the calculation of HCDP measurements.)
For each optical system, light from a light-emitting diode (LED) is
directed to a mirror surface through a Polycarbonate Window. The
optic-path windows are truncated cones and thus will remain seated
rmly even with high-pressure gas samples in the Measuring Cell.
The placement of the optic-path windows and Phototransistors are not
symmetric, as suggested by Figure 1-3. These elements are located,
by design, so that when condensation occurs – either hydrocarbon on
the rough surface, or water on the smooth surface – the intensity of
light at the respective phototransistor increases. This arrangement is
possible because of the dierent wetting properties of the two types of
liquids.
O-ring The gas sample chamber is formed by the Mirror Support and the
cavity machined within the aluminum cylinder. The gas seal between
the two parts is created by an o-ring.
Sample Inlet/Outlet The Sample Gas Inlet and Outlet channels are simply bored through
the aluminum cylinder. Both the Sample Inlet and Outlet connections
contain ame arrestors.
Pressure Regulator Used to adjust the sample gas ow rate. This regulator is labelled
“Flow Adjustment” on the analyzer backpan.
Purge Air (Gas) The purge air (gas) supply creates a dry atmosphere within the
Thermoelectric Cooler (TEC) compartment to prevent ice from forming,
which can damage the cooler.
Purge/Shut In Solenoid Valve Controls the ow of the sample gas. At the start of the Purging/Hold
Stage, the solenoid valve is opened to allow the sample gas to purge
through the Measuring Cell. At the end of the Purging/Hold Stage, the
solenoid valve is closed to stop the ow and to enable the Measuring
Cell to equilibrate to the process stream pressure.
Relief Valve The overpressure Relief Valve, which is set to release at 13.8 BARG
(200 PSIG), prevents the solenoid valve from becoming over-
pressurized (attaining full line pressure) in the case of a failure of the
pressure regulator.
Bypass Valve The Bypass Valve allows a small ow rate during the measuring cycle.
The ow rate through the bypass is approximately one-tenth of the
Purge/Hold Stage cycle ow (called a “trickle purge”).
Vent Line Vents the used sample gas to atmosphere or to an approved low
pressure (<50 PSIG) are header
.
Electrical Leads The analyzer is controlled by a single Microcontroller board which,
along with the power supplies and other electronic components,
is contained in an enclosure separate from the Measuring Cell
Assembly (Figure 1-4). Communication between the Microcontroller
board and the Measuring Cell Assembly is via Electrical Leads which
pass through the Measuring Cell seal mounting assembly. The
Microcontroller monitors the mirror temperature, controls the mirror
cooling rate, adjusts the brightness level of the LEDs, monitors the
light intensities at the phototransistors, controls the sample valve, and
determines whether a dewpoint is detected.
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