ABB CM30 User Manual page 21

ControlMaster CM30 and CM50
Universal process controllers,
...Basic
Loop 1 (2) Control
On/Off Hysteresis
Mode
Autotune
IM/CM/ED–EN Rev. B
1 1
/ and / DIN
4 2
Sets the hysteresis value in engineering units.
Note. Applicable only if Control Type is On/Off – see page 39.
PV
ON
OFF
Reverse Acting Control Output
Turns the Autotune functionality on or off. When set to On, an Autotune can be started from
the Operator level menus – see page 16.
Autotune is a user-activated feature that enables automatic setting of the controller PID
parameters (see page 20) using an
controller output and then monitors the process response to calculate the optimum PID
settings. Autotune uses a relay-type function with hysteresis that initiates a controlled
oscillation in the process. New PID parameters are calculated and stored in the controller
automatically.
Note. To achieve the best results from Autotune, switch the controller to Manual control
mode (see page 6) and adjust the output until the PV is stable (close to the normal setpoint)
before initiating Autotune.
Autotune Operation
The Autotune sequence is shown in the following figure:
SP
PV
Setpoint
PV
Hysteresis
Value
ON
OFF
Direct Acting Control Output
'
at setpoint type
1 Set the first step value and dynamics required. For best
results, select the largest initial output step size that can
be tolerated by the process.
2 Autotune is enabled only if the control type is PID.
3 Start Autotune from the Operator menu.
4 Monitors a noise A and calculates a hysteresis
.
value
5 User-defined initial step in the output B. When the
process exceeds the hysteresis value the output is
stepped down.
6 Adjusts output amplitude automatically C so PV
disturbance is kept to minimum required.
7 When consistent oscillation is established D, the
Autotune process stops. Optimum settings are
calculated from the process dynamics monitored.
6 Basic Level
Hysteresis
Value
Setpoint
'
algorithm. Autotune changes the
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