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C.PB
SP + cSPo
SP
H.PB
+100%
0%
-100%
Tuning output only with proportional action in case of
proportional heating band separate from cooling band.
SP
C.PB
SP + cSPo
H.PB
+100%
0%
-100%
Tuning output only with proportional action in case of pro-
portional heating band suforimposed on cooling band.
5.10.6. Heat/Cool tuning with relative gain
For this tuning mode (enabled on the PID menu with
parameter Cntr = PID.RG) you have to specify the cooling
type (COOL parameter).
The PID cooling parameters are calculated starting from
heating parameters in the specified ratios:
•
Air
relative gain H.PB / C.PB = 1
•
Water
relative gain H.PB / C.PB = 0.8
•
Oil
relative gain H.PB / C.PB = 0.4
Example
Starting with the following heat data:
•
COOL = oil
•
H.PB = 10.0
•
H.IT = 4.00
•
H.DT = 1.00
there will be the following cool data:
•
C.PB = 12.5
•
C.IT = 4.00
•
C.DT = 1.00
PV
Time
PV
Time
80209C_MHW_850-1650-1850_01-2020_ENG_pag. 205
For slicing cycle times for outputs, the following values
should be set:
•
Air
CY.TIM Cycle T Cool = 10 seconds
•
Water
CY.TIM Cycle T Cool = 2 seconds
•
Oil
CY.TIM Cycle T Cool = 4 seconds
Attention! Cool parameters cannot be changed in
this mode.
5.10.7. Cascade controls
setpoint
PRIMARY
CONTROLLER
IN.1
PID1
PRIMARY
noise
SENSOR
PROCESS
Two controllers are arranged in cascade when the output
signal from the first becomes the input signal to the second,
which in turn sends a signal to the control unit.
The primary controller compares the controlled variable to
the setpoint, while the secondary controller compares the
value of the controlled variable to the signal from the primary
controller.
Cascade control provides faster control of the primary
variable value.
In addition, the primary variable is less subject to deviations.
The secondary controller keeps the flow constant, changing
it only when instructed by the primary controller.
The cascade controller is used especially in very slow
processes. In these processes, the error is recovered over
a long time, and when noise enters the process, you have
to wait a long time before the error is revealed and before
corrective action begins; therefore, the corrective action
does not start immediately. After the action has started, you
have to wait a long time for the result.
A cascade control is built by finding intermediate controlled
variables that can forform rapid corrective actions in case of
noise.
The primary and secondary controllers are arranged in
cascade: each has its own process variable but only the
secondary one has an output that commands the process.
The main advantages of cascade control are:
•
noise in the secondary loop is corrected by the
secondary controller before it can affect the primary
variable;
•
delays in the secondary part of the process are
significantly reduced by the secondary loop, and this
increases primary loop response speed;
•
gain changes in the secondary part are compensated
in its chain;
•
the secondary loop lets the primary controller act
precisely on the flow of material or energy.
SECONDARY
CONTROLLER
IN.2
PID2
SECONDARY
ACTUATOR
SENSOR
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