AFS-G1
page 4
AFS-G1 K04/1019
5. Operating Principle
The Hygrostat AFS-G1 serves as a two-position controller to regulate relative
humidity indoors or in air ducts.
The humidity sensing element in the sensor comprises several strips of plastic
fabric, each with 90 fibres of 3 µm diameter. These plastic fibres undergo a
special process to acquire hygroscopic properties, meaning that they will absorb
and release humidity. The molecular structure of the fibres changes when they
absorb water, giving rise to a measurable change in length. The length of the
plastic fibres is thus a measure of the relative humidity.
The swelling effect, acting primarily in longitudinal direction, is transferred over a
suitable lever system to a microswitch with an extremely small changeover
movement.
The measuring element reacts quickly and accurately to the change in air
humidity. The setpoint is set with the setpoint button so that the microswitch is
actuated by the lever system when the humidity setpoint is reached.
The special treatment of the measuring element ensures that its hygroscopic
properties remain stable, and that is sensitivity is maintained until destroyed by
external influence. Regeneration found in conventional instruments is not
required, but is also not damaging.
The harp-shaped measuring element is protected by a perforated probe tube and
is open to the housing. The Hygrostat is designed for use in unpressurised
systems.
The humidity measuring equipment is designed with a perforated sensor tube.
The humidity and temperature measuring elements are located in the interior of
the sensor tube. The humidity measuring element is arranged axially and the
temperature measuring element is seated sideways at the top or bottom between
the perforation holes.
The measurement accuracy depends on the degree of pollution of the element.
The humidity measuring element, in particular, loses its hygroscopic properties if
the surface is covered with grease, soot, smoke deposits, paint, resinous
substances, etc. By cleaning the elements, their function can be reproduced, but
only if no damage is caused by acids, alkaline solutions or other aggressive
substances (see Maintenance).
