Desiccant - Delta-T Devices AP4 User Manual

Hints and Tips
head printed circuit board. Try not to get rest of the circuit board wet. The electronics do
not like water. Leave it for a full day to dry out. Some chemicals are known to produce
permanent damage or a calibration shift in the RH sensor. Avoid all organic solvents and
their vapours, cigarette smoke, Sulphur dioxide and other sulphurous pollutants.

DESICCANT

Check the colour of the desiccant in the drying tube about once a week.
Recent AP4s are supplied with desiccant which is orange when dry and green when wet.
Note: Earlier AP4s had desiccant which changed from blue to pink when wet.
Please note that the current advice from the desiccant manufacturer is not to attempt to
regenerate the desiccant by heating, but to replace it.
They also say desiccant is damaged above 120°C
A 500 g pot of 2-5 mm beads of orange to green self-indicating silica gel is currently
supplied with each AP4. The amount used in the AP4 silica gel tube is about 16 g so the
pot may supply about 30 refills, if you store the pot in a dry place and close the lid
immediately after use.
In tropical high humidity environments, if you are changing the desiccant weekly, the
500 gm pot might last 6 months. But if you expose this to the high humidity, even for a
short period, the lifetime will be reduced.
In contrast, at Delta-T in the UK, our technical support people have a pot of desiccant,
used for occasional AP4 repairs, which is two years old and still good.
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