TM_i-BX(-N)_NC05_00_06_20_EN
MEHITS S.p.A.
●
TECHNICAL MANUAL
Version NC05 - Translation of the Original Instructions
68
9
ANNEXES
9.1
PID REGULATION
The Nadisystem software includes the PID regulator, which allows the regulation of the inverter compressor.
The graph below shows the operating logic of a PID control:
+
Setpoint
I
t
t
d
e
K
0
)
(
P
D
)
(
t
e
K
p
dt
t
de
K
d
)
(
Process
Error
Output
-
This type of control involves three types of action:
•
P
roportional action
•
I
ntegral action
•
D
erived action
The values of the three types of action can be modified to change the effects of the controlled output variable and therefore the effects on the
regulation 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.
In i-BX(-N) units the regulation parameters can be found in the Service menu. The regulation is of the P+I type and the involved parameters are 0506,
0509 and 0512.
The machine regulation (cool or heat) is a function of the temperature value read by the system exchanger output probe.
Below are a few guidelines concerning the effect of each action.
9.1.1
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 Kp (also known as proportional gain) calculated with this formula:
𝐾
𝑝
=
100
𝐵
𝑝
Where Bp is the value of the proportional band defined by one of the following parameters:
•
0507 and 0510 for the regulation of the heat and cool temperature
•
0513 for the regulation of the DHW temperature
The proportional band Bp defines the maximum error capable of bringing the proportional action to 100%.
A low Bp 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 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
(Decreases)
Constant
(Increases)
Promptness of
response
Overshoot
Balancing time
Error at full
power
Stability
Bp
Kp
Increases
Increases
Decreases (slightly)
Decreases
Worsens
9.1.2
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.
