8.3 Desiccant
To prevent liquid water from coming in contact with any electronics, the internal humidity must
be maintained at non-condensing levels. The CSAT3BH has an on-board relative humidity sensor
that continuously monitors the humidity inside the enclosure. This humidity ranges between 0
and 100%. As temperature decreases, the capacity of air to hold water also decreases, and the
relative humidity will increase even if no additional water has been introduced into the closed
system. As the relative humidity approaches 100%, condensation will begin to form on the
internal surfaces. Other electronic components, however, are not equipped with sensors and,
therefore, the user must implement some maintenance plan in which desiccant changeout is
either done as routine maintenance or by routine checks of the indicator card inside the
enclosure.
The CSAT3BH has a cavity to hold a replaceable desiccant canister that removes water from the
air (see
(p. 86)). Water molecules will unavoidably ingress into the electronics over
time, so the internal humidity of the CSAT3BH head should periodically be checked. This can be
done automatically with a data logger if the data logger program uses the
CSAT3BMonitor()
instruction in
CRBasic Editor
, or manually by connecting a CSAT3BH to a computer using the USB
cable and then launching the
Device Configuration Utility
. Under the Settings Editor tab of the
utility, there is secondary tab for Real-Time Data, where the internal humidity measurement will
be displayed along with various other measurements.
If monitoring shows the internal humidity of the CSAT3BH rising above 50%, including during
nighttime cooling cycles, the desiccant should be replaced with canisters that can be purchased
from Campbell Scientific. The small canister holds desiccant and is installed on the underside of
the anemometer block inside the brass screw cap (see
(p. 86)). Use a large flat-
headed screwdriver to unscrew the cap and remove the canister. Replace the old canister with an
unused one.
The new canister should appear blue in color. A pink-hued canister indicates that moisture has
been absorbed, and the canister should be discarded and replaced with a new one. When
replacing the brass screw cap, ensure the cap is tightened until the head of the screw is flush with
the housing and the o-ring cannot be seen.
NOTE:
Replacement desiccant canisters are shipped in a vacuum-sealed bag. The bag should not be
opened until the canisters are to be inserted into the anemometer block.
Desiccants are shipped with an expiration date. The expiration date reflects the date by which the
desiccant should be properly installed in the instrument.
CSAT3BH Three-Dimensional Heated Sonic Anemometer
85
