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INSTRUCTIONS FOR INSTALLATION AND USE.
4.4.2. P
-
ROPORTIONAL
INTEGRAL CONTROL
inserting an integral action into the control system. The integral action time, 1IT,
determines the speed of cancellation of the error, but a high speed (1IT low) may be
the cause of overshoot and instability in the response. The integral part normally acts
within the proportional band, but this area of action may be reduced in terms of
percentage by lowering the integral action reset 1AR. The response overshoot is thus
decreased. The integral control is cancelled when the temperature goes outside the
area of action of the integral part. With 1IT=0 the integral control is disabled.
4.4.3. P
-
ROPORTIONAL
INTEGRAL
controlled by a PI controller may be reduced by inserting a derivative action in the
control. The derivative action is greater the faster the temperature variation within the
time unit. A controller with a high derivative action (1DT high) is extremely sensitive to
small temperature variations and can make the system instable. With 1DT=0 the
derivative control is disabled.
4.5. M
. Following a sensor malfunction,
ALFUNCTIONING
of the parameter 1PF.
CAUTION: when programming the hysteresis 1HY or the proportional band 1PB, it is advisable to consider the number of switchovers
that the relay will carry out and, if necessary, adapt the cycle time in order to limit the frequency of switchover.
5. AUTO-TUNING
5.1. B
. Before starting the auto-tuning procedure, ensure that the output has been set with PID control, the proportional
EFORE STARTING
band has the sign corresponding to the required mode of operation (heating/cooling) and that the set point has been fixed at the required
value. The auto-tuning procedure is divided into two parts. In the first part, the operator has to characterise the process to be controlled
by fixing the cycle time. In the second, the controller acquires the responses of the system to certain stresses for efficient adaptation of
the control parameters.
5.2. S
TARTING THE FUNCTION
PID mode (1Y=PID), 1CT starts to blink on the display. Press
displayed simultaneously. Using
first phase the auto-tuning function may be quit by pressing key
30 seconds without touching the keyboard.
5.3. A
CQUISITION OF RESPONSES
temperature value appear alternately on the display. If there is a power failure during this phase, the next time the instrument is
switched on, after the initial internal self-test phase, it continues the auto-tuning function. To manually abort the auto-tuning function
without modifying the control parameters, keep button
Upon successful completion of auto-tuning, the controller updates the value of the control parameters and starts to control.
5.4. E
. If the auto-tuning procedure is unsuccessful, an indication of the error that has caused the failure blinks on the display:
RRORS
timeout error 1: the controller has not succeeded in bringing the system temperature within the proportional band. Temporarily
increase the set point with control in the heating mode and vice versa in the cooling mode, then restart the procedure.
timeout error 2: the auto-tuning procedure has not finished within the maximum set time (1000 cycle times). Restart the auto-tuning
procedure and set a higher cycle time.
temperature over range: after having checked that the error has not been caused by a sensor malfunction, temporarily decrease
the set point with control in the heating mode and vice versa in the cooling mode and then restart the procedure.
To erase the error indication and return to the normal mode, press the key
5.5. C
ONTROL IMPROVEMENT
to reduce overshoot, decrease the integral action reset 1Ar;
to increase the response speed of the system, decrease the proportional band 1Pb; caution: doing this makes the system less stable;
All manuals and user guides at all-guides.com
. The steady-state error is cancelled by
-
. Response overshoot in a system
DERIVATIVE CONTROL
. To access the auto-tuning function, keep the keys
+
or
, change the cycle time to characterise the dynamics of the process to be controlled. In this
SET
. The keyboard is disabled throughout the whole acquisition phase, while
. If the resulting control is unsatisfactory, proceed as follows:
appears on the display and the output is controlled according to the value
+
to confirm selection of the channel; the current parameter value is
SET
. The acquisition phase starts upon pressing the keys
pressed for 3 seconds.
.
Overshoot
1SP
1PBx1AR%
integral control
Process
action area
temperature
Time
Figure 4 Proportional-Integral Control (PI) in heating mode
Overshoot
1SP
Process
temperature
Time
Figure 5 Proportional-Integral-Derivative Control (PID)
in heating mode
pressed for 3 seconds. If the output is in the
and the measured
1PB
1PB
+
or after
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