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VAPOR-LOGIC
®
VERSION 6 INSTALLATION AND OPERATION MANUAL
Settings menu
The Settings menu is where system parameters
can be changed. This menu is used primarily
during initial installation, but can also be
used for making changes or adjustments as
needed during operation. Note that while all
parameters can be changed, many changes
also require a corresponding hardware
change. Vapor-logic firmware will warn you of
this during the setup process.
See Setup, beginning on Page 27, for more
information about the Settings menu.
When your system has a humidity or dew point transmitter, you can adjust
and control the set point through the touchscreen or Web interface using a
proportional, integral, and derivative (PID) control loop.
IMPROVES HUMIDIFIER RESPONSE TIME
With a PID loop, you can tune your system for maximum performance using the
proportional (Kp), integral (Ki), and derivative (Kd) gain terms.
Kp = Proportional gain factor
Ki = Integral gain factor
Kd = Derivative gain factor
These gain factors work in the following way: The overall demand in a PID
system is made up of three distinct parts—the proportional, the integral, and
the derivative. Each of these parts is calculated and then multiplied by its
corresponding gain factor. These gain factors are the setup variables you have
access to from the Settings menu. By making a gain factor larger, you increase
its overall influence on system demand. Once each PID component is multiplied
by its gain factor, all three terms are added together to determine the overall
demand percentage.
THE PROPORTIONAL TERM
The proportional term is the difference between the RH set point and the
actual humidity multiplied by the proportional gain. For example, with a Kp
of 80 and the actual humidity 5% below the RH set point, the proportional
contribution to the demand is:
5 × 80 × 0.085 = 33% (the 0.085 is an internal scalar used to increase the
usable span of Kp).
There is a problem with using only proportional gain to control the RH. In
almost all applications there is some constant load on the humidifier just
as there is a constant load on heating equipment. If the proportional term
is all that is used, the actual humidity must be less than the set point for the
humidifier to be on.
What happens is the humidifier finds a happy medium where the actual
humidity is something less than the set point, which allows the humidifier to
continue to run. This difference between the set point and the actual running
humidity level is called the droop. This droop can be corrected using the next
term, the integral.
PID tuning
OPERATION
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