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5. Examples and applicative notes
5.10.4. Auto-Tuning
Enabling the Auto-Tuning function blocks the settings of the
PID parameters.
There are two types: continuous and one-shot.
Continuous Auto-Tuning constantly measures system oscil-
lations, immediately searching for PID parameter values that
reduce the current oscillation. It does not act if the oscilla-
tions drop to values below 1.0% of the Proportional Band.
It is interrupted if the setpoint changes and automatically re-
sumes with a constant setpoint.
The calculated parameters are not latched if the device swi-
tches off, if it goes into manual, or if the configuration code is
disabled.
The controller resumes with the parameters programmed be-
fore enabling Auto-Tuning.
The calculated parameters are latched when the function,
enabled from digital input or key
One-shot" Auto-Tuning can be started manually or automa-
tically. It is useful for calculating PID parameters when the
system is around the setpoint.
"One-shot" Auto-Tuning produces a change in the control
output up to a maximum of ± 100% of current control power
(limited with H.P.HI...H.P.LO for heat and with C.P.HI...C.P.LO
for cool) and evaluates the effects in time overshoot.
The calculated parameters are latched. It starts manually via
digital input or via Tuning key after an undershoot/overshoot.
It starts automatically (with error band of 0.5%) when the
PV-SP error goes beyond the set band (programmable at
0.5%,1%, 2%, 4% of full-scale).
Attention! At power-on or after a setpoint change,
automatic start is inhibited for a time equal to five
times the integral time (with minimum of 5 minu-
tes). The same time has to pass after running "One-
shot" Auto-Tuning.
5.10.5. Examples of tuning
The two diagrams below show the time change in the moni-
tored value and the change in the controlled tuning output.
•
PV = Process variable
•
SP + cSPo = cooling setpoint
•
cSPo = C.SP (HI.SCL - LO.SCL) / 100
•
C.PB = Proportional cooling band
•
SP = heating setpoint
•
H.PB = Proportional heating band
C.PB
SP + cSPo
SP
H.PB
+100%
0%
-100%
146
, is disabled.
PV
Time
tempo
Tuning output only with proportional action in case of pro-
portional 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 superimposed on cooling band.
5.10.6. Heat/Cool tuning with relative gain
For this tuning mode (enabled on the PID menu with para-
meter 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
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.
80208G_MHW_650-1250-1350_01-2017_ENG
PV
Time
tempo
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