PID ROCKWELL
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Transcript of PID ROCKWELL
Copyright © 2011 Rockwell Automation, Inc. All rights reserved.
PID and PIDE Getting Started Guide for ControlLogix and CompactLogixBruce KyerRA Technical Support Engineer
Conference Call Information
US Dial 866-774-1453 Conference ID: 25089971
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 2
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 3
Agenda
1. Introduction
2. Parameter Overview
3. Demos
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 4
Adding the Ladder PID and Tags
• Enter the following for the ladder PID:
A backing tag of type PID for
internal storage
The tag that holds the PV value
The output tag that you’ll use to drive the process
(CV)
A Tag for operator manual control if desired, or leave
0 if not used
These are display values from PID backing tag
Set these three fields to zero if you don’t use them
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 5
Configuring the PID - Scaling Tab
Engineering units: This is what the setpoint is
specified in and what the status below uses.
Unscaled Min/Max: This should match the range
from the input card
The range the PID will use for its output
This is the range the Tieback tag will use
If you change while the processor is running, you
must uncheck this box once
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 6
Configuring the PID - Alarms Tab
• The PID has built-in alarming.– Can be used by the program to indicate that the PV is out of range.– Is not essential for PID operation - does not have to be used.
Specify alarm limit values if desired, or leave all 0 if
you don’t use.
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 7
Configuring the PID - Configuration Tab
Choose independent or dependent equation form.
This affects tuning.
Choose the Control Action
PV–SP or SP-PV
Choose Derivative of PV or Error
Enter the desired Loop Update Time
Enter Deadband value. Freezes CV when PV is “close enough”. Can save on valve wear or help stabilize system. Leave 0 if not used.
Additional Options
Enter a range to limit the CV to. Enter 100
and 0 for no limit
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 8
Configuring the PID - Tuning Tab
Setpoint is what the PID tries to drive the PV to.
Output bias, also known as feedforward, is directly added to the output.
Manual mode feeds the Tieback tag directly
to the PID output.
Enter the PID gains here. These numbers can be
adjusted to tune the loop.
Current values and status to monitor PID state.
Use Set Output to directly control the output when software manual is
checked.
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 9
Adding the Ladder PID - Timing
• The Ladder PID is not self-regulated (timed). – Needs to be regulated with Timer or Periodic Task, otherwise, output will be wild.– PID should only be executed as fast as process needs to conserve CPU resources.– The period at which the PID is scanned true should be filled into the Loop Update
Time. Programmer must make sure that this is filled in manually or update programmatically PID_Backing_Tag.UPD.
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 10
Adding a Function Block PIDE and Tags
• The Function Block PIDE Connect process measurement tag
Connect a tag for manual output
control
Set True for Program Control
Connect the process control tag
Set for the mode desired
Connect a tag for setpoint
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 11
Configuring the PIDE – EUs/Limits Tab
Specify the range for CVEU to use (the PIDE
output).
Engineering units. This is the range the PV and SP
use. The PV input is assumed to be in EU.
Make sure status says “OK”
Limits the CV and SP to a sub-range. Make sure this
is filled in after setting scaling. Typically, SP limit
is same as PV.
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 12
Configuring the PIDE – General Config Tab
Specify the gains.Usually best to leave mode periodic. In
that case, PIDE will regulate itself.
Choose control action and equation
type
More advanced settings, can normally
leave alone.
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 13
Demos
• PID
• PIDE
Copyright © 2011 Rockwell Automation, Inc. All rights reserved. 14
References
• Using the PIDE Instruction White Paper• Logix5000 Controllers Advanced Process Control Reference Manual• Logix5000 Controllers General Instructions Reference Manual• This presentation and the associated ACD example will be attached to
Knowledgebase ID 462378