30.14.2.2 PID Monitor
In Monitor Step, for PID instructions used on the Logic screen,
you can check the operation of PID values. You can also change each
parameter.
Target PID Variable
Select the PID variable that you want to monitor.
List of PID Adjustments
You can input values and adjust the PID while referring to the
graph.
Graph Display
The PID instruction values are displayed in a graph that can be
monitored.
Graph
You can specify the details of the graph. Click and the settings
dialog box appears.
Displayed Items
Select the check box to display [Current Value], [Target Value],
[Output Value], [Output Invalidity Range], or [Output Range].
Graph Display Range
Specify [Upper Limit], [Lower Limit] and [Width] for the graph
display range.
Update
The graph must be updated with the values specified for the PID
adjustment.
Undo
Return to the state before PID adjustment values were input.
PID Adjustments
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Items
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Value
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Setpoint (SP)
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Specify the target value. Enter values for the minimum and
maximum output. The range for input depends on the PID instruction
output settings. For details, refer to the PID instructions.
 Chapter 31 Logic
Instruction List
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Tieback (TB)
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Specify a value for output during power off. The range for input
depends on the PID instruction output settings. For details, refer
to the PID instructions.
Chapter 31 Logic
Instruction List
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Proportional Constant
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Specify the proportion for comparison control. A larger value
means that the target value will be reached sooner. A smaller value
means the set point will be approached more gradually, resulting in
reduced overshooting. The setting range is from 0.01 to 100.00. For
details about proportional constants, see the next page.
Proportional Operation (P)
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Integral Calculus Time
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Specify the intervals between integral calculations. The setup
range is from 0.00 to 3000.00 seconds. For details about integral
calculus time, see the following.
Integral
Operation (I)
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Differential Calculus Time
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Specify the intervals between differential calculations. The
setup range is from 0.00 to 3000.00 seconds. For details about
differential calculus time, see the following.
Derivative Operation (D)
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Processing Deadband Range
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Specifies the range in which the PID operation does not run. The
deviation in the settings range is "0", and the processing deadband
range is based on +/- from the Set Point. The settings range from 0
to (maximum output value -minimum output value) / 2.
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Bias
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The value specified here is added to the output value for
operation. The settings range from the minimum output value to the
maximum output value.
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Sampling
Frequency
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Specify the sampling frequency for the PID operation. The
frequency depends on the scan time and the PID instruction is
operated in the scan after the specified frequency. The settings
range from operation frequency to 65535 (ms).
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Proportional Operation (P)
Calculate the operation volume (output value) proportionate to
the deviation (deviation between the set point and current value).
The formula for the relation between deviation (E) and operation
volume (CV) is as follows.
CV = KP x E
(KP is the proportional gain.)
When the deviation is fixed, the proportional action is as
follows.
The operation volume changes within the range of 0 to 4095
(initial value). As KP increases, the operation volume
proportionate to the deviation increases and the correcting action
is strengthened. This proportional action causes offset (residual
deviation).
Integral Operation (I)
Continuously change the operation volume (output value) to
eliminate any deviation (deviation between the set point and
current value). Doing so can eliminate the offset from the
proportional action.
Once deviation is caused in the integral action, the operation
volume of the action changes to the operation volume of the
proportional action. The time required for the change is called the
"integral calculus time." The time is indicated as TI. A smaller TI
results in a stronger integral action.
If the deviation is fixed, the integral action is as
follows.
Use integral action as "PI action" combined with the
proportional action or as "PID action" combined with the
proportional and derivative action." You cannot use integral action
alone.
Derivative Operation (D)
Add the operation volume (output value) proportionate to any
deviation (deviation between the set point and current value) to
eliminate deviation. Doing so prevents the control target from
drastically changing due to an external disturbance.
Once deviation has occurred in the derivative action, the
operation volume of the action changes to the operation volume of
the integral operation. The time required for the change is called
the "differential calculus time" and is indicated as TD.
A larger TD results in stronger derivative action.
If the deviation is fixed, the derivative action is as
follows.
Use derivative action as "PD action" combined with the
proportional action or as "PID action" combined with the
proportional action and integral action. You cannot use derivative
action alone.
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