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TM_s-MEXT_ME28relC_00_12_19_EN
21
ANNEXES
21.1
PID ADJUSTER CONTROL PARAMETERS
The EVOLUTION+ software is equipped with some PID adjusters for controlling:
•
Cold request
•
Humidifier
The graph below shows the operating logic of a PID control:
This type of control involves three types of action:
•
Proportional action
•
Integral action
•
Derived action
The values of the three types of action can be modified to change the effects on the controlled output variable (inverter frequency, valve opening, steam production, fan
speed, etc.) and, therefore, the adjustment itself.
The default parameters of the controller allow sufficiently precise and rapid adjustment within the response times. However, in certain cases it may be necessary to make
certain changes depending on the required result of the adjustment.
The parameters can all be set under the "Regulations" menu, which can be accessed by entering the "Service" password.
For the default values, see the parameters table.
Below are a few guidelines concerning the effect of each action.
21.1.1
Proportional Action
The proportional action sets a basic control action for what is currently happening. The value of this action is proportional to the error, i.e. the deviation of the measured unit
in relation to the setpoint.
This action is defined using the proportional constant K
Where B
is the value of the proportional band defined by one of the following parameters:
p
•
P20.18 (for temperature adjustment)
•
P20.21 (for humidity adjustment)
The proportional band B
defines the maximum error capable of bringing the proportional action to 100%.
p
A low B
value can therefore cause an extreme reaction even when there are slight variations in the error, while a high value ensures little variation of the control variable
p
even when there are serious errors.
The following table shows the reactions on the system caused by the decrease of the proportional band and resulting increase of the proportional constant.
Parameter
Constant
(Decreases)
(Increases)
B
K
p
p
21.1.2
Integral Action
The integral action is an action of control on the basis of what has happened in the past. The value of this action is proportional to the sum of the errors of the previous
moments.
This action is defined using the integral constant K
T
is the value of the integral time defined by one of the following parameters:
i
•
P20.05 (for the adjustment of direct expansion units with on/off compressor or chilled water units)
•
P20.06 (for the adjustment of direct expansion units with inverter compressor)
•
P20.22 (for humidifier adjustment)
•
P20.95 (for the adjustment of direct expansion units with compressors with delivery air adjustment active and Free Cooling).
The following table shows the reactions on the system caused by the decrease of the integral time and resulting increase of the integral constant.
Technical manual
+
Setpoint
∑
Error
-
Figure 21-1: PID operating control logic
(also known as proportional gain) calculated with this formula:
p
Promptness of
response
Increases
(also known as integral gain) calculated with this formula:
i
P
K
e
) (t
p
t
I
∑
Process
K
e
(
)
d
t
0
de
) (
t
D
K
d
dt
100
��
=
��
��
��
Overshoot
Balancing time
Increases
Decreases (slightly)
��
��
��
=
��
��
��
123
Output
Error at full power
Decreases
TRANSLATION OF THE ORIGINAL INSTRUCTIONS
Stability
Worsens
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