The Lead Compensator block attempts to remove some of the dynamics of a control loop. This process results in forward-looking predictions and speeds up controller responses. The effect is similar to adding derivative action to the controller. Lead compensation is incorporated into most zone temperature control processes where oversized or nonlinear valves might be applied. The Lead Compensator block only exists within a Control Sequence or Control Activity within a Control Sequence.
The Lead Compensator primitive provides the following reliability values: Reliable, Input Out of Range, or Math Error. The Present Value retains its previous value on Math Error. The block remains Reliable if the Input is not Reliable (ignores unreliability of the input).
The following table describes the inputs and outputs of the Lead Compensator logic block.
|
Name |
Data Type |
Exposed for Connection by Default |
Description |
Default Value |
|---|---|---|---|---|
|
Inputs |
||||
|
Count |
Float |
Yes |
Indicates the number of executions performed by the PID. This value is used to ensure that this block only runs its execute method when the PID that drives the block runs. |
0.0 |
|
Input |
Float |
Yes |
Provides an input to this logic block from the connected PID. This input is referred to as u k in the equations defined in the Present Value description. If the input is less than the Low Limit, the Low Limit value is used. If the input is greater than the High Limit, the High Limit value is used. |
0.0 |
|
High Limit |
Float |
Yes |
Indicates the maximum value the Lead Compensator Present Value can assume. If the High Limit is set to a value less than the Low Limit, the block’s reliability is set to Input Out of Range and the logic continues to use the last reliable pair of values. See the Low Limit description for the behavior when High Limit equals Low Limit. |
100.0 |
|
Low Limit |
Float |
Yes |
Indicates the minimum value that the Lead Compensator Present Value can assume. The Low Limit must be less than or equal to the High Limit. If the Low Limit is set to a value greater than the High Limit, the block’s reliability is set to Input Out of Range, the logic sets the Present Value to the Low Limit, and behaves the same as if the limits are equal. If the Low Limit is set to the same value as the High Limit, the logic sets the Present Value to this value. These inputs may be equal, therefore, the block’s Reliability is not set to Input Out of Range. |
0.0 |
|
Time Constant |
Float |
Yes |
Indicates the time constant of the process being controlled. This value usually comes from a PID Pre-Processor. |
900 |
|
Outputs |
||||
|
Present Value 1 |
Float |
Yes |
Provides an output from the Lead Compensator logic block, calculated by the following equations:
|
0.0 |
|
Properties |
||||
|
Actual Period |
Float |
N/A |
Indicates the length of time since the last execution of this block. |
1.0 second |
|
Lambda |
Float |
N/A |
Indicates the value used by the block. See the equations defined in the Present Value description. |
0.8758 |
|
Last Input |
Float |
N/A |
Indicates the input at the time of the last execution of this block. This value is the same as the Input on the first execution of this block on startup, or on an enable after a disable. |
0.0 |
|
Last Output |
Float |
N/A |
Indicates the output at the time of the last execution of this block. This value is the same as the Input on the first execution of this block on startup, or on an enable after a disable. |
0.0 |
