STULZ Ultra-Series Humidifier Controller
(August, 2013)
13
P/I- Proportional/Integral Control
4.1.3
The controller calculates proportional control output
signal(s) based on the analysis of sensor input signals,
which determines the amount of humidification needed (see
Figure 12).
Figure 12 - Control Logic
Signal 1 represents the return air humidity and is calculated
by the controller as a percentage value compared to the
maximum control set point value for input 1, taking into
account the prop band. Signal 1 is compared to the
maximum control set point value for input 1 resulting in a
control value that will be proportional to signal 1. Signal 2
represents the limit humidity and is calculated as a
percentage value for input 2 taking into account the prop
band. Signal 2 is compared to the maximum control set
point value for input 2 resulting in a control value that will be
proportional to signal 2. The control output signal to the
Humidifier(s) will be directly proportional to the combined
input signals by the following process:
Signal 1 x Signal 2
100
If input 2 is not used, the controller only works with
reference to signal 1. The effect of integral on the control
signal (Signal 1) has been neglected from the above
calculation for simplification. With integral control, the
added element of time is factored into the Humidifier output
algorithm. The integral value is used to gradually adjust the
proportional output when the calculated output does not
move the process variable closer to set point in a given
period of time. Decreasing the integral value decreases the
interval for the output corrections (speeding the rate of
adjustment). Increasing the integral value increases the
interval for corrections (slowing the rate of adjustment). The
P/I control factors are hard coded in the controller and
cannot be user adjusted.
