Process Restart Inhibit (PRI)
This information applies to the CompactLogix 5380P and ControlLogix 5580P controllers.
Use the Process Restart Inhibit (PRI) instruction for Large Motor (PRI) instruction to prevent large motors from starting repeatedly. The high starting current for a large motor causes heating. Continual starts or start attempts in a short period overheat the motor windings and damage the motor.
The PRI instruction provides a rule-based state model for restarts. Do not use the instruction to model or monitor heating and replace sensor-based motor monitoring devices. Use the instruction to avoid overstressing a motor.
Available Languages
Ladder Diagram
Function Block Diagram
Structured Text
PRI (PRI tag);
Operands
IMPORTANT:
Unexpected operation may occur if one of the Cold or Hot timers are set to 0.
Configuration Operands
Operand | Type | Format | Description |
|---|---|---|---|
PlantPAx Control | P_RESTART_INHIBIT | tag | PRI structure |
P_RESTART_INHIBIT_INPUT Structure
Public members are standard (visible) Tag members that are programmatically accessible. Private (hidden) members are used in HMI faceplates and are not programmatically accessible. Private members are listed in separate tables after public members.
Public Input Members | Data Type | Description |
|---|---|---|
EnableIn | BOOL | Enable Input - System Defined Parameter
Default is true. |
Inp_Stopped | BOOL | 1 = Equipment is confirmed stopped. Default is false. |
Inp_Starting | BOOL | 1 = Equipment is confirmed starting, indicating a start attempt. Default is false. |
Inp_Running | BOOL | 1 = Equipment is confirmed running. Default is true. |
Cfg_ThreeColdStarts | REAL | Time within which three starts are allowed if cold (hr) Default is 0.5. |
Cfg_FirstFailCold | REAL | Time for cold motor to wait after 1st start failure before ready to start (hr) Default is 0.5. |
Cfg_SubseqFailCold | REAL | Time for cold motor to wait after 2nd and subsequent start failure before ready (hr) Default is 4.0. |
Cfg_FirstFailHot | REAL | Time for hot motor to wait after 1st start failure before ready to start (hr) Default is 0.5. |
Cfg_SubseqFailHot | REAL | Time for hot motor to wait after 2nd and subsequent start failure before ready (hr) Default is 4.0. |
Cfg_HotRestartOK | REAL | Time for hot motor to run so it can immediately restart after stop (hr) Default is 1.0. |
Cfg_RestartHot | REAL | Time for hot motor to wait after stop if stopped before Hot Restart OK time (hr) Default is 1.0. |
Cfg_HotToCold | REAL | Time for a stopped hot motor to become cold (hr) Default is 16.0. |
Inp_InitializeReq | BOOL | 1 = Request to initialize the instruction. The instruction is normally initialized in instruction first run. Use this request when reinitialization is needed. The instruction clears this operand automatically.
Default is true. |
Public Output Members | Data Type | Description |
|---|---|---|
EnableOut | BOOL | Enable Output - System Defined Parameter |
Val_MinToReady | DINT | Minutes yet inhibited before ready to start (for display as countdown mmm:ss). |
Val_SecToReady | DINT | Seconds yet inhibited before ready to start (for display as countdown mmm:ss). |
Sts_bFdbk | SINT | Device feedback: 0 = None/Multiple/Unknown, 1 = Stopped, 2 = Starting, 3 = Running. |
Sts_State | SINT | State number for highlighting state diagram on HMI. See Instruction Help or state diagram in reference manual. |
Sts_Ready | BOOL | Permissive for equipment to start: 1 = Ready to start, 0 = Not ready, inhibit starting. |
Sts_Err | BOOL | 1 = Error in configuration: invalid time. Valid = 0.0 to 596.52 hours. |
Sts_Initialized | BOOL | 1 = Instruction is initialized. Use Inp_InitializeReq to reinitialize. |
Operation
The PRI instruction provides these capabilities:
- Provides a rule-based state model for restarts and is not intended to model or monitor the motor heating.
- Display of the time before ready state; the time is displayed in minutes and seconds and is configurable. The ready state is also displayed independently of the time.
- Ready status is determent by the cold ready to start time (First start) and the hot ready to start time.
- The cold ready to start time will be determent by the cold first fail time and the cold subsequent fail time.
- The hot ready to start time will be determent by the hot first fail time, the cold subsequent fail time and the hot restart delay time.
Configuration of Strings for HMI
Configure strings for HMI faceplates and for the
Logix Designer
configuration dialog box. The strings are set to extended properties of tag items. Configure the strings in the Logix Designer
application only. - Description
- Label for graphic symbol
- Display Library for HMI Faceplate call-up
- Instruction name
- Area name
- URL link
Implementation
This illustration shows normal implementation with the input condition mapped to Inp_Running, Inp_Starting, and Inp_Stopped on a separate branch.
This illustration shows the implementation with the input condition mapped to the PRI instruction using the rung-condition-in. When the rung-condition-in is false (EnableIn is false) the instruction executes normally. To use the rung-condition-in mapping method, set Inp_Running to 1, its default value.
Monitor the PRI Instruction
Use the operator faceplate from the PlantPAx library of Process objects for monitoring.
Affects Math Status Flags
No.
Major/Minor Faults
None specific to this instruction. See Index Through Arrays for array-indexing faults.
Execution
Ladder Diagram
Condition/State | Action Taken |
|---|---|
Prescan | Rung-condition-out is cleared to false. |
Instruction first run | The instruction executes normally. |
Rung-condition-in is false | Set rung-condition-out to rung-condition-in. |
Rung-condition-in is true | Set rung-condition-out to rung-condition-in. The instruction executes. |
Postscan | Rung-condition-out is cleared to false. |
Function Block Diagram
Condition/State | Action Taken |
|---|---|
Prescan | EnableOut is cleared to false. |
Instruction first run | See Instruction first run in the Ladder Diagram table. |
Instruction first scan | See Instruction first run in the Function Block Diagram table. |
EnableIn is false | EnableOut is cleared to false. |
EnableIn is true | EnableOut is set to true. The instruction executes. |
Postscan | EnableIn and EnableOut bits are cleared to false. |
Structured Text
In Structured Text, EnableIn is always true during normal scan. Therefore, if the instruction is in the control path activated by the logic it will execute.
Condition/State | Action Taken |
|---|---|
Prescan | See Prescan in the Function Block Diagram table. |
Instruction first run | See Instruction first run in the Function Block Diagram table. |
EnableIn is true | See EnableIn is true in the Function Block Diagram table. |
Postscan | See Postscan in the Function Block Diagram table. |
Example
In this example, tag A100_MR_001 is the motor value monitored by the PRI instruction.
Inp_Running is connected to the Motor Running status tag (A100_MR_001.Sts_Running) that comes from the Sts_Running output of the P_Motor instruction instance for this motor (A100_MR_001). Inp_Starting is connected to the Motor Starting status tag (A100_MR_001.Sts_Starting) that comes from the Sts_Starting output of the P_Motor instruction instance for this motor (A100_MR_001). Inp_Stopped is connected to the Motor Stopped status tag (A100_MR_001.Sts_Stopped) that comes from the Sts_Stopped output of the P_Motor instruction instance for this motor (A100_MR_001).
Finally, PRI_01 is the output tag that will indicate the status of A100_MR_001 with appropriate delays and number of running and starts/attempts based on whether the motor is allowed to start again.
Ladder Diagram
Function Block Diagram
Structured Text
PRI_01.Inp_Stopped := A100_MR_001.Sts_Stopped;
PRI_01.Inp_Starting := A100_MR_001.Sts_Stopped;
PRI_01.Inp_Running := A100_MR_001.Sts_Running;
PRI(PRI_01);
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