PID Configuration Dialog Box - Configuration Tab Overview
Use this tab to initially configure the PID instruction.
Parameters
PID Equation
Indicates the type of equation. A 1 indicates Dependent gains; 0 indicates Independent gains (.PE).
Use Independent when you want the three gain terms (P, I, and D) to operate independently. Use Dependent when you want an overall controller gain that affects all three gain terms (P, I, and D).
Control Action
Indicates the direction of control. Choose from the following.
- 0 means E=SP-PV
- 1 means E=PV-SP
Derivative Of
Indicates whether the derivative term in the PID equation acts on changes to the Process Variable (PV) or the Error value.
Loop Update Time
Enter the update time (.UPD) for the instruction (greater than or equal to 0).
CV High Limit
The maximum allowable value for the Control Variable. This is the maximum CV value the system can tolerate. The PID instruction does not output a CV that exceeds the High Limit.
In the PID configuration dialog box, the alarms bits are the fields on the right in the status area. There are eight status bits. These bits are within the .CTL member of the PID tag. These bits are described under PID Structure within the PID instruction.
CV Low Limit
The minimum allowable value for the Control Variable. This is the minimum CV value the system can tolerate. The PID instruction does not output a CV less than the Low Limit.
In the PID configuration dialog box, the alarms bits are the fields on the right in the status area. There are eight status bits. These bits are within the .CTL member of the PID tag. These bits are described under PID Structure within the PID instruction.
Deadband Value
The error range above and below the setpoint. Enter "0" to inhibit the deadband. If scaled, the deadband has the same scaled units as the setpoint.
The adjustable deadband lets you select an error range above and below the setpoint where output does not change as long as the error remains within this range. This deadband lets you control how closely the process variable matches the setpoint without changing the output. The deadband also helps to minimize wear and tear on your final control device.
No Derivative Smoothing
No Derivative Smoothing equals 1.
The derivative calculation is enhanced by a derivative smoothing filter. This first order, low pass, digital filter helps to minimize large derivative term spikes caused by noise in the PV. This smoothing becomes more aggressive with larger values of derivative smoothing. You can disable derivative smoothing if your process requires very large values of derivative gain (K
d
> 10, for example). To disable derivative smoothing, select the "No derivative smoothing" option on the Configuration tab or set the .NDF bit in the PID structure.No Bias Calculation
You can disable back-calculation of the .BIAS term by setting the .NOBC bit in the PID data structure. Be aware that if you set .NOBC true, the PID instruction no longer provides a bumpless transfer from manual to auto when integral control is not used.
No Zero Crossing for Deadband
Disables the PID from using zero-crossing. This causes the PID instruction to consider the error to be zero any time the process variable is within the deadband; otherwise, the PV is not considered in the deadband during the period after it enters the deadband range and before it crosses the SP.
PV Tracking
Indicates whether the setpoint tracks the PV in manual control mode for bumpless transfer to automatic control mode. A "1" indicates PV Tracking; "0" indicates no PV Tracking.
Cascade Loop
Indicates if this PID is part of a cascaded loop. A "1" indicates YES; "0" indicates NO.
Cascade Type
Indicates the type of loop if the PID is part of a cascaded loop; 1 indicates Master, 0 indicates Slave.
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