Global parameters of control loops
(Original Document)
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At a Glance
Some parameters associated with control channels may be separated in three categories:
The Task parameter can be modified in the general parameters area of the configuration screen, whereas the execution and instrumentation parameters can be modified in the configuration area.
PLC Task
This table describes the PLC task parameter:
Parameter
Description
Task
The process control channels must be assigned to a PLC task, either MAST or FAST. The MAST task is selected by default. Select the FAST task if you wish to improve the sampling speed and execution priority.
Instrumentation Parameters
This table describes the instrumentation parameters for the process control loop:
Parameter
Description
Name
This name is included in the constants (%KW); it may be assigned to each loop. The name may consist of a maximum of eight characters.
Unit
This parameter, with a maximum of 6 characters, is included in the constants (%KW). These characters define the process control loop unit (Example: DEGREE).
Application ID
This parameter identifies the process control loop configuration. To check their authenticity, these application IDs may be compared to each other. They numerically represent the loop's configuration constants.
Any modification to parameters for the KP unit significantly affects the application ID. One should note, however, the following specificities of cascade and auto-selector loops:
  • cascade loop: Any modification to parameters for the KP unit on one of the loops (master or slave) is instantly reflected on this parameter for both loops. However, the application ID is modified only for the slave loop.
  • auto-selector loop: Any modification to parameters for the KP unit on one of the loops (main or auto-selector) is instantly reflected on this parameter for both loops. However, the application ID is modified only for the secondary loop.
Upper Scale
Lower Scale
These thresholds define the physical scale within which the loop controls the process. The upstream branch calculations (process value and setpoint) are both set to the same scale.
Note: the setpoint branch includes a scaling function which returns the variable scale range, as previously defined during setpoint input. This function is useful when process loops are chained together to form a cascade. By default, this scale must be identical to the physical scale defined by the loop.
Note: it is also possible to set the output branch to a specific scale.
"Command Order" double word
Use the Command Order double word to manage loop operation. It replaces the WRITE_CMD function. For the first 16 bits, this double word is identical to the process control loop status word.
Execution Parameters
This table describes the control loop execution parameters.
Parameter
Description
Sampling period
This is the loop controller's processing period, in automatic mode. The default value is 0.3 seconds. This value must be a modulo of the task period. Otherwise, the process control cyclical processing will default to the nearest modulo.
Example: T_MAST = 0.1 s, T_ECH = 0.124 s T_ECH true = 0.1 s
If
Then
the sampling period is less than the task period
the true sampling period is automatically fixed to that of the task period.
Period calculations are made taking into account the true value of T_ECH. If the task processing execution time exceeds the theoretical period, the error is reflected in the OVERRUN bit %S19.
Trigger method
The Process Control Loop can be triggered automatically