Yokogawa Data Acquisition with PID Control CX2000 - Manual (Page 69)

1-57
IM 04L31A01-01E
Explanation of Functions
3
2
1
4
5
6
7
8
9
10
11
12
13
14
Auto Tuning
Auto tuning is a function that automatically measures the process characteristics and
automatically sets the optimum PID constant. When auto tuning is executed, the control
ouput is temporarily turned ON/OFF step-wise (see the following figure). From the
hunting period and amplitude of the PV that is generated, the optimum PID constant is
calculated and set. This method is called the limit cycle method. Auto-tuning is allowed
only during auto operation under PID control. In addition, for cascade control, auto
tuning on the primary loop is possible only when cascade operation is in progress.
Setpoint
Process
value
Control
output
Auto tuning on
PID control according to
the PID control determined
by auto tuning
Auto tuning ends
on the third hump.
Auto tuning in progress
OFF OFF
ON ON ON
Time
Target Setpoint during Auto Tuning Execution (Auto Tuning Point)
The auto tuning point can be limited in the range of 3 to 97% of the measurement span.
Auto tuning points are indicated below.
• When Zone PID is selected
Local operation
When specified group is in operation: SP specified by the SP number
When all groups are in operation: Midpoint of each reference point
Program operation or remote operation
When specified group is in operation: SP when auto tuning is executed
When all groups are in operation: Midpoint of each reference point
• When Zone PID is not selected
Local operation
SP specified by the SP number
Program operation or remote operation
SP when auto tuning is executed
(However, the secondary loop of cascade control is the SP specified by the SP
number)
Note
If auto tuning is executed when any of the loops set to program control enabled (includes the
case when program control is enabled on the primary loop of cascade control) is in program
operation, the progress of the program operation is temporarily paused. The time event and
segment time are prolonged by the amount of time the program operation is paused. The
program operation is resumed when auto tuning on all loops set to program control enabled is
complete. When program operation is temporarily paused, hole operation, advance operation,
and PV event are valid. However, wait operation is invalid.
1.12 Tuning