15
5.1 Auto Calibration (AutoCal)
The
AutoCal
facility uses the fact that each sensor is designed and manufactured
to give no further increase in response when it reaches its maximum moisture
level.
For example
a SDHmini with a full scale value of 0 °C dewpoint will read
0 °C dewpoint when exposed to a gas with this moisture concentration and will
continue to read 0 °C dewpoint as the moisture concentration rises above 0 °C
dewpoint.
The SDHmini can therefore be adjusted to read 0 °C dewpoint on any gas with a
moisture concentration wetter than 0 °C dewpoint, ambient air for instance, thus
setting the span to match the original calibration.
NOTE:
For instruments with a dewpoint range above 0 °C, e.g. the Blue range, -80 to +20 °C,
please refer to section
5.2 Calibration Setpoint (CalSet)
.
Select
AutoCal
from the
Configuration Menu
.
Please ensure that the inlet and outlet valves are open to
atmosphere.
Extend the desiccant head on the instrument (as illustrated on
the instrument screen) noticing that the value of the full scale
moisture level has already been automatically preselected as a
target of 0 °C. You may need to lift the head two to three times
to allow ambient air through to the chamber, ensuring inlet
and outlet are unrestricted. Press .
The SDHmini will display a moving bar until it assesses that
the sensor has stabilised (please allow up to ten minutes for
this to occur).
The SDHmini will now display the full scale value of the unit,
either -20 °C or 0 °C depending on the sensor range.
Close the desiccant head when instructed to do so and press
.
