LI-COR LI-6400, Manual

Page: 221 / 846

Environmental Control
Humidity Control
Using the LI-6400 7-7
Pressing
enter
with no entry will retain the target variable. Entering a value
will change back to fixed target mode.
Variable targets are a powerful tool, but do have a possible limitation when
combined with AutoPrograms. See
AutoPrograms and the Control Man-
ager on page 25-19.
Humidity Control
Humidity control in the LI-6400 is done by a combination of two mecha-
nisms:
1 Incoming humidity
The mechanism for controlling incoming humidity is manual: the amount of
incoming air that is routed through desiccant is set by the adjust valve on the
top of the desiccant tube, allowing incoming humidities to range from ambi-
ent to dry. (You could also moisten the air - see
Humidifying Incoming Air
on page 4-50).
2 The flow rate of air through the chamber
The flow of air through the chamber is controlled by the software, either by
controlling pump speed (CO
2
mixer not installed) or diverting excess flow
(CO
2
mixer installed).
The Operational Envelope
The manual bypass control defines the operating envelope within which the
automatic flow controls can operate. By forcing more of the flow through the
desiccant, the operating window (upper and lower limits of humidity) de-
creases; when less air is forced through the desiccant, the window increases
(Figure 7-8).