ControlMaster CM30, CM50 and CMF310
Universal process controllers,
1
/
4
,
1
/
2
DIN and fieldmount
6 Basic Level
IM/CM/ED–EN Rev. X
29
…Basic
Loop 1 (2) Control
On/Off Hysteresis
Sets the hysteresis value in engineering units.
Note
. Applicable only if
Control Type
is
On/Off
– see page 49.
Mode
Turns the
Autotune
functionality on or off. When set to
On
, an
Autotune
can be started from
the
Operator
level menus – see page 23.
Autotune
Autotune
is a user-activated feature that enables automatic setting of the controller
PID
parameters (see page 30) using an
'
at setpoint type
'
algorithm.
Autotune
changes the
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:
PV
PV
ON
OFF
Reverse Acting Control Output
Setpoint
Hysteresis
Value
Hysteresis
Value
Setpoint
Direct Acting Control Output
ON
OFF
A
B
C
D
SP
PV
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.