Carel k.Air, User Manual, Page: 57 / 192

57
Functions k.air +030220981 rel. 1.2 - 01.12.2020
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100%
0%
St
Reg_var
Request (%)
Diff_1
D1
100%
A
0%
St
Reg_var
Request (%)
Diff_1
Diff_2
D2
30220980_156_R01
Key
Request Request
Reg_var Control variable
A Off set
St Set point
Diff _1/2 Diff erential 1/2
Fig. 9.k Fig. 9.l
Note :
the examples use the term diff erential, while gain (kp) is used in the sett. The relationship is diff erential=100/kp.
If the fi rst device has a lower limit “Lim1” for the activation request, it will be activated as shown in Fig. L1. Similarly for the
second device, shown in Fig. L2.
30220980_157_R01
100%
0%
St
Reg_var
Request (%)
Diff_1
L1
Lim1
100%
A
Lim2
0%
St
Reg_var
Request (%)
Diff_1
Diff_2
L2
30220980_158_R01
Key
Request Request
Reg_var Control variable
Lim1 Minimum activation limit for
device 1
A Off set
St Set point
Diff _1/2 Diff erential 1/2
Lim2 Minimum activation limit for
device 2
Fig. 9.m Fig. 9.n
Sequence control if devices not available
If there are two devices that can be activated to meet a request and the fi rst is not available, the request is sent to the second.
If in the meantime the fi rst device becomes available again, the second is kept active and the fi rst is activated at 100% output.
This makes the response faster.
9.5.3 Incremental P I D
Incremental PID is the most common control mode on k.air. It is used for a single point control and is based on a PID controller
designed to avoid variations in the output in the event of variations to the set point.
Typically, the output is always limited between a minimum and maximum control value.
The incremental PID is used in the following algorithms:
• Dehumidifi cation control
• Humidifi cation control
• Fan fl ow or pressure control
• Control for auxiliary loop
• Supply limit control
• etc.
For each control point, the following are typically available:
• kp, proportional gain (diff erential = 100/kp)
• ti, integral time
• td, derivative time
• minimum and maximum control limits.
9.5.4 D ead band
For all types of control, where the dead band is confi gured and if the control probe reading is inside the dead band, the probe
continues to be controlled, but the output is not modifi ed. When the signal moves outside of the dead band, the output is in-
creased, or decreased, without sudden variations.
30220980_173_R01
100%
0%
Set
B
Req
NZ/2 diff
Key
Req Request
Set Set point
NZ. Dead band
Alarm Alarm
diff Diff erential
B
Control probe
Fig. 9.o