Kahn Optidew Bench Top, User Manual

Page: 39 / 88

Optidew User’s Manual
30 October 2019
OPERATION
4 OPERATION
4.1 Operating Cycle
Figure 24 Typical operating cycle
At initial switch-on, the instrument enters a DCC cycle for 2 minutes. During this time the
mirror is heated above the prevailing dewpoint to ensure that all condensate is driven
off the surface of the mirror. The degree of heating is determined by the configuration
of the ‘Type’ and ‘Setpoint’ parameters in the DCC menu (see section 3.2 for further
information).
The mirror is maintained at this temperature for the DCC period (default 4 minutes) or
2 minutes on switch-on. During the DCC process, Data Hold fixes the analog outputs
at the same value(s) as before DCC commenced. Data Hold typically lasts 4 minutes
from the end of a DCC cycle, or until the instrument has reached the dewpoint. This
procedure is in place to prevent any system which is connected to the outputs from
receiving a 'false' reading.
After the DCC period has finished, the measurement period commences, during which
the control system decreases the mirror temperature until it reaches the dewpoint. The
sensor will take a short amount of time to form a film of condensate and control on the
dewpoint. The length of this stabilization time depends upon the dewpoint temperature.
When the measurement is stable or tracking very slow changes in dewpoint, the Sensor
indicator in the Operational Status display will indicate ‘Control’. Note that at dry
dewpoints (below around -4°F/-20°C) the sensor may display ‘Control’ when the mirror
temperature is still slowly oscillating, always use the trend graph on the display as a
secondary indication.
The end of a DCC cycle re-sets the interval counter, meaning that another DCC will start
(by default) after 4 hours have elapsed. Once the measurement is stable, Data Hold will
release, and the analog outputs will resume their normal operation. At this point the
Status area of the Operational Status display will change to ‘Measure’.