Cooling Stage - Ametek 241CE II User Manual

If any of these diagnostic checks fail, the Possible-Cell-Contamination ("w Dirty
Cell") SCode is generated and the Purging/Hold Stage is repeated. The Purg-
ing/Hold Stage will then be extended by a duration equal to the purge cycle
time (PTime). If not already done, you can also open the Bypass Valve (on the
analyzer backpan, Figure 2-1) to allow a very low purge flow rate (trickle purge)
to flow continuously through the Measuring Cell. This flow will be approxi-
mately 10 percent of the Purging/Hold Stage flow.
Since the analyzer uses only the Measuring Cell, sample gas, and Heatsink as
heat sources to warm the mirror, it is possible at the end of the Purging/Hold
Stage for the mirror temperature to be less than its High setpoint temperature.
This is a frequent occurrence when the purging time is short and the differ-
ence between the ambient temperature and the High setpoint temperature
of the mirror is minimal. When this occurs, the Cooling Stage is initiated and
the Stage-Time-Out ("w TimeOut") SCode and Purging/Hold-Stage-Time-Out
("w Hold TimeOut") XSCode are generated.

Cooling Stage

The Cooling Stage begins immediately after the Purging/Hold Stage is com-
plete. During this stage, the temperature of the mirror is decreased linearly at
the preset Fast Cooling Rate [FRate, default = 5 °C/minute (9 °F/minute)] from
its upper (High) setpoint temperature until the mirror temperature reaches a
preset temperature, typically 15 °C (27 °F) above the last determined HCDP
temperature of the sample gas. This value is set in the ApplicCFG : Above
menu. After this temperature is reached, the mirror is then cooled at the preset
Slow Cooling Rate [SRate, default = 2 °C (3.6 °F)] per minute – to its Low set-
point temperature, typically -30 °C (-22 °F).
In the initial measuring cycle after power-up or a system reset, the mirror is
cooled at the SRate for the entire stage.
The Low setpoint temperature should be lower than the HCDP temperature of
the sample gas but not more than 60 °C (140 °F) degrees below the ambient
temperature and never lower than -40 °C (-40 °F).
2-32 | 241CE II Hydrocarbon Dewpoint Analyzer
AMETEK does not recommend changing the Slow Cooling Rate
(SRate). This rate was tested at the factory for optimum HCDP dew-
point sensitivity.
PN 903-8797, Rev A