ENVI
®
Control
31
1.8.4.7.9
Integral rate
This parameter in the ENVI is the time in seconds that the boiler control calculates the deviation
from setpoint and responds to drive the output towards setpoint.
The I-term is the integration factor as it applies to the ENVI. Every second the error between sensor
input and setpoint is added to the sum of errors. This sum, divided by the I-term and
added to the output power generated by the P-factor as described above. So if the sensor
input stays below the setpoint this internally calculated sum increases and therefore the
SUM divided by I-term increases so the PID output increases. If you increase this value the
input of this sum of errors reduces and the system becomes slower.
For example: With an Integral rate at the default setting of 50 and a header setpoint of 140
°
:
If the header temperature is at 130
° (
10
°
below SP
) the integral rate of adjustment
will add 0.2
°
to the setpoint.
10
(degrees below setpoint) ÷
50
(Integral rate) =
0.2
The ENVI control will add 0.2
°
to the setpoint making the effective setpoint
140.2
°
(By changing the effective setpoint in the logic, this increases the action towards
setpoint)
Integral rate continues to adjust the control output in accordance with both the size of the deviation
from setpoint and the time it lasts to bring the process to setpoint regardless of load
1.8.4.7.10 Der time {Derivative time}
Derivative time setting in the ENVI control serves as a bias setting for the Proportional band.
If the Derivative time setting is at the default setting of 128 or above, the proportional band is below
the setpoint. See figure 2 on page 30.
If the Derivative time setting is at the alternate setting of 0 up to 127, the proportional band is
symmetrical around the setpoint. See figure 1 on page 30
.
1.8.4.7.11 Cyc lmt incrmnt {Cycle limit increment}
Each time a starting or stopping of a boiler is detected, a cycle limit increment is added to the
switch boiler counter. Every minute of cycle run time this counter is decreased by one (1). Only if
the switch boiler counter value is below Cycle limit max can boilers be switched on or off. This
feature prevents the boilers from short cycling, leading to increased boiler lifespan.
1.8.4.7.12 Cycl limit max {Cycle limit max}
This parameter is the maximum amount of time allowed for the boiler to short cycle based on the
cycle limit increment parameter and the switch boiler counter value. Once the switch boiler counter
