Dcc; Data Hold Phase - Michell Instruments Optidew User Manual

Optidew Series User's Manual
3.3.3

DCC

Dynamic Contamination Control (DCC) is a system designed to compensate for the loss
of measurement accuracy which results from mirror surface contamination.
During the DCC process the mirror is heated to approximately 20°C above the sensor
temperature to remove the condensation which has formed during measurement.
The surface fi nish of this mirror, with the contamination which remains, is used by
the optics as a reference point for further measurements. This removes the effect of
contamination on accuracy.
At switch-on, the system initiates a DCC to measure the surface condition of the mirror.
The status LED will be lit to indicate a DCC is in progress and the Channel 1 mA output
will be fi xed at 23 mA. The end of the DCC duration will result in the system resuming
automatic control of the mirror temperature and cooling the mirror surface to form
condensation. The instrument will be in DATA HOLD mode until the instrument has
settled on the dew point and the measurement is stable.
For more information about the operating cycle of the Optidew, and DATA HOLD mode
refer to Sections 3.4.2 and 3.4.4.
3.3.4

DATA HOLD Phase

During DATA HOLD, the level of the Channel 1 mA output is held and the Status Relay
and Status LED are energized and illuminated respectively, until the system has stabilized
onto the measured dew point. The DATA HOLD phase will fi nish when the following two
conditions are met:
• The minimum hold time has expired and
• The system is stable to within a specifi ed stability band
The minimum hold time is nominally set to 4 minutes, and generally, under most
conditions, the system will be stable within this time period. However, there may be some
conditions where the system may take longer to stabilize, so under these conditions
an adaptive hold algorithm takes over to determine when stability is reached. If, under
extreme conditions, the system fails to stabilize within the set stability band, the DATA
HOLD phase will terminate when the maximum hold time is reached.
When the DATA HOLD phase fi nishes - the Status LED will turn off, the Status Relay will
de-energize and the hold on Channel 1 mA output will be released. The system will now
be in its continuous measurement phase, where it will remain until the measurement
time has elapsed and the next DCC cycle initiates.
Michell Instruments
OPERATION
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