Operating Modes
The Cascade/Ratio, Auto, and Manual modes can be controlled by a user program when in Program control or by an operator interface when in Operator control. The Override and Hand modes have a mode request input that can only be controlled by a user program; these inputs operate in both Program and Operator control.
Operating Mode | Description |
Cascade/Ratio | While in Cascade/Ratio mode the instruction computes the change in CV. The instruction regulates CV to maintain PV at either the SPCascade value or the SPCascade value multiplied by the Ratio value. SPCascade comes from either the CVEU of a primary PID loop for cascade control or from the “uncontrolled” flow of a ratio-controlled loop. Select Cascade/Ratio mode using either OperCasRatReq or ProgCasRatReq: Set OperCasRatReq to request Cascade/Ratio mode. Ignored when ProgOper, ProgOverrideReq, ProgHandReq, OperAutoReq, or OperManualReq is set, or when AllowCasRat is cleared. Set ProgCasRatReq to request Cascade/Ratio mode. Ignored when ProgOper or AllowCasRat is cleared or when ProgOverrideReq, ProgHandReq, ProgAutoReq, or ProgManualReq is set. |
Auto | While in Auto mode the instruction computes the change in CV. The instruction regulates CV to maintain PV at the SP value. If in program control, SP = SPProg; if in Operator control, SP = SPOper. Select Auto mode using either OperAutoReq or ProgAutoReq: Set OperAutoReq to request Auto mode. Ignored when ProgOper, ProgOverrideReq, ProgHandReq, or OperManualReq is set. Set ProgAutoReq to request Auto mode. Ignored when ProgOper is cleared or when ProgOverrideReq, ProgHandReq, or ProgManualReq is set. |
Manual | While in Manual mode the instruction does not compute the change in CV. The value of CV is determined by the control. If in Program control, CV = CVProg; if in Operator control, CV = CVOper. Select Manual mode using either OperManualReq or ProgManualReq: Set OperManualReq to request Manual mode. Ignored when ProgOper, ProgOverrideReq, or ProgHandReq is set. Set ProgManualReq to request Manual mode. Ignored when ProgOper is cleared or when ProgOverrideReq or ProgHandReq is set. |
Override | While in Override mode the instruction does not compute the change in CV. CV = CVOverride, regardless of the control mode. Override mode is typically used to set a “safe state” for the PID loop. Select Override mode using ProgOverrideReq: Set ProgOverrideReq to request Override mode. Ignored when ProgHandReq is cleared. |
Hand | While in Hand mode the PID algorithm does not compute the change in CV. CV = HandFB, regardless of the control mode. Hand mode is typically used to indicate that control of the final control element was taken over by a field hand/auto station. Select Hand mode using ProgHandReq: Set ProgHandReq to request hand mode. This value is usually read as a digital input from a hand/auto station. |
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