Operating instructions

38
TP modulation
The standard form of modulation with an electric
humidifier is TP (time-proportioning) modulation.
With this type of modulation, the outputs are cycled
on and off at a certain rate to approximate humidifier
demand.
For example, if a VAPORSTREAM
®
humidifier has
four heat output stages (four contactors) and a
demand of 55%, two of the contactors will be
energized all of the time, one contactor will be
cycling on and off at a certain rate, and one contactor
will be off all of the time. The rate at which the third
contactor cycles is determined by the demand and the
TP cycle time. Continuing with our example, if we
have a TP cycle time of 60 seconds and a demand of
55%, the third contactor will be cycling at a rate of
12 seconds on and 48 seconds off.
To calculate the above example, imagine that each
contactor represents 25% of the output of the
humidifier. With a 55% system demand, we need two
full contactors plus 5/25 of a third contactor.
Therefore, two contactors will be full on and a third
contactor will be on for 5/25 of 60 seconds, or 12
seconds.
To minimize wear on the contactors that are cycling,
VAPOR-LOGIC
®
3
keeps track of the number of
cycles on all contactors and it will rotate the TP
cycling contactor through the stages to ensure that
they all get equal wear. In addition, no contactor will
ever have a cycle time of less than two seconds or
greater than two seconds less then the TP cycle time.
In other words, if a contactor needs to be on for less
than two seconds because of the way the math turns
out, the contactor will be energized for the minimum
two second period. Also, if a contactor needs to be
de-energized for less than 2 seconds, it will stay on.
This prevents quick cycling of the contactors and
extends their life. On a TP system with contactors,
the TP cycle time is user-adjustable and can be set
from 30 seconds to 99 seconds via the
VAPOR-LOGIC
3
keypad/display.
Operation:
TP modulation
Modulation types: TP modulation.
Operation