Effective Use of PID Features for Loop Performance and

Optimization Greg McMillan CDI Process & Industrial

Hector Torres Solutia Inc.

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Presenters

Greg McMillan Principal Consultant Email: Greg.McMillan@Emerson.com 33 years Monsanto-Solutia Fellow 2 years WU Adjunct Professor 8 years DeltaV R&D Contractor BS Engineering Physics MS Control Theory Hector Torres Senior Process, Control Engineer

Specialist Email: hhtorr@solutia.com 16 years Solutia Inc. Six Sigma Black Belt BS Control Theory MS industrial Engineering

Key Benefits

DeltaV PID options and parameters can: – Provide maximum disturbance rejection – Minimize setpoint overshoot and rise time – Eliminate limit cycles – Reduce valve maintenance – Coordinate loops for consistency and minimal interactions – Increase process efficiency – Increase feed rates – Protect equipment – Protect Environment – Enable wireless control – Enable analyzer control

PID Features Covered

PID options and parameters: – Anti-Reset Windup (ARW) and Output Limits – Auto Tuner and Adaptive Controller – Dynamic Reset Limit – Structure – Integral Deadband – Nonlinear Gain – Feedforward – Output Tracking – Setpoint Filter – Setpoint Rate Limits – PIDPlus

Application Examples Given

PID Features exemplified by following applications: – Fast generic continuous loop with nonlinear valve – Slow bioreactor batch loop with integrating response – Fast generic batch loop with integrating response – Valve with backlash and stick-slip – Surge valve open loop backup – Conductivity and pH kicker – Valve position control for prime movers, chillers, & reactors – Wireless control – Analyzer control

ARW and Output Limits

ARW limits set equal output limits for precise valves For Digital Valve Controllers (DVC) & Fisher valves

– ARW & Out Lo Lim = 0%, ARW & Out Hi Lim = 100%

For pneumatic positioners & on-off heritage valves – Lo Lim = -5%, Hi Lim = 105% – ARW set inside output limits to get thru zone of ineffective

valve response (stick-slip, shaft windup, & poor sensitivity)

Auto Tuner and Adaptive Control

Set PV filter before tuning – Set PV filter time large enough to keep PID output fluctuations from

noise within control valve deadband (e.g. < 0.25%) – Insure PV filter time < 0.1x current reset time (sec)

Make output step big enough to see process response – Use output step size > 0.2x PID Gain – Use output step size > 4x backlash and stick-slip – Use Structure with Proportional Action on Error

Use auto tuner for initial settings at operating point – Check “Integrating Processes” and 3 cycles for slow processes (use

near-integrating process approximation to speed up test) Setup adaptive tuner regions

– Use Out as state parameter for nonlinear valve – Use PV as state parameter for nonlinear process (e.g. pH)

Nonlinear Valve Auto Tuning

click on PID tag and then Tune

Check box for near integrating process approx

Nonlinear Valve Adaptive Tuning

Process gain is approximately proportional to flow for

equal percentage flow characteristic

Nonlinear Valve Model Viewing

Identification Out Limit that sets deadzone low output limit should be set approximately equal to valve deadband and stick-slip near closed position

Nonlinear Valve Learning Setup

Nonlinear Valve Simulate Tests

Click on margin plot to see tuning and simulation response

Bioreactor Adaptive Control

External-Reset Feedback Gain

E-R is external reset (e.g. secondary %PVs) Dynamic Reset Limit

Σ

%SP β

derivative

∗

∗

∗ ∗ ∗

Rate

∆

∆

γ

%COp

filter

filter

%PV filter Filter Time = α ∗ Rate Time

Σ

filter

Filter Time = Reset Time

E-R

Positive Feedback

All signals are % of scale for PID algorithm

Out1

Out2

Σ

∆

P FF

D

Feedforward

filter Σ

P

FF

D

Filter Time = Reset Time

Back out positive feedback of Feedforward (FF) and

ISA Standard Form of Proportional (P) and Derivative (D) modes

with β and γ factors

∗

−

+

−

+

∆ +

−

+ −

P = (β −1) ∗ Gain ∗ %SP

PID Structure Options

(1) PID action on error (β = 1 and γ = 1) (2) PI action on error, D action on PV (β = 1 and γ = 0) (3) I action on error, PD action on PV (β = 0 and γ = 0) (4) PD action on error, no I action (β = 1 and γ = 1) (5) P action on error, D action on PV, no I action

(β = 1 and γ = 0) (6) ID action on error, no P action (γ = 1) (7) I action on error, D action on PV, no P action (γ = 0) (8) Two degrees of freedom controller

(β and γ adjustable 0 to 1)

(1) PID action on error

Fastest response to rapid (e.g. step) SP change by

– Step in output from proportional mode – Spike in output from derivative mode can

be made more like a bump by decreasing gamma factor (γ <1)

– Zero deadtime from deadband, resolution limit, & stiction

Burst of flow may affect other uses of fluid

Operations do not like sudden changes in output

Fast approach to SP more likely to cause overshoot

Setpoint filter & rate limits eliminate step & overshoot

(2) PI action on error, D action on PV

Slightly slower SP response than structure (1) – Still have step from proportional mode – Spike or bump from derivative mode eliminated

Decrease in SP response speed is negligible if – Output hits output limit due to large SP change or PID gain – Rate time is less than total loop deadtime – Alpha factor is increased (α > 0.125) (rate filter increased)

Setpoint filter & rate limits eliminate step & overshoot Most popular structure choice

(3) I action on error, PD action on PV

Provides gradual change in output for SP change Slows down SP response dramatically Eliminates overshoot for SP changes Used for bioreactor temperature and pH SP changes

(overshoot is much more important than cycle time) Used for temperature startup to warm up equipment Generally not recommended for secondary loops

Effect of Structure on SP Response for Self-Regulating Process

Setpoint filter could have eliminated overshoot

Structures 2, 3 and 8

β and γ SP weighting factors are adjusted to balance fast approach & minimal overshoot for SP response

Simpler method is setting SP filter time = reset time

Structure (8) Two Degrees of Freedom

(4 - 5) No Integral action

Used if integral action adversely affects process

Used if batch response is only in one direction

Must set bias (output when PV = SP) Highly exothermic reactors use structure 4

because integral action and overshoot can cause a runaway

– 10x reset time (Ti > 40x deadtime) to prevent runaway

Traditionally used on Total Dissolved Solids (TDS) drum and surge tank level control because of slow integrating response and permissibility of SP offset.

– Low controller gain (Kc) cause slow rolling oscillations due to violation of inequality for integrating process. The following inequality

is commonly violated since Ki (integrating process gain) is extremely small on most vessels (Ki < 0.00001 %/sec/%).

iic KTK /2≥∗

Typical Batch Temperature

01020304050607080

1 51 101 151 201 251 301 351 401

Time (min)

degr

ees

C

Setpoint PV CO%

Batch temperature response in a single ended temperature control. Integral action causes overshoot.

Batch Temperature (new tuning)

0.05.0

10.015.020.025.030.035.040.045.0

1 51 101 151 201 251 301 351 401

Time (min)de

gree

s C

Setpoint PV CO%

Batch temperature response in a single ended temperature control. PD on error. No I action.

(6 -7) No Proportional Action

Predominantly used for valve position control (VPC)

– Parallel valve control (VPC SP & PV are small valve desired & actual position, respectively, & VPC out positions large valve)

– Optimization (VPC SP & PV are limiting valve desired & actual position, respectively, & VPC out optimizes process PID SP)

– VPC reset time > 10x residence time to reduce interaction

– VPC reset time > Kc∗Ti of process PID to reduce interaction

– VPC tuning is difficult & too slow for fast & large disturbances

Better solution is dynamic reset limit & SP rate limits

Valve position control increases precision and rangeability

Effect of Structure on SP Response for Integrating Process

Setpoint Filter and Feedforward

Process

Measurement

Feedforward Summer

Control Valve

Measurement

Feedback Controller

AI

AO

SP

PV

OUT

Disturbance

setpoint feedforward

Filter

setpoint filter time is simply equal to feedback controller reset time

Feedforward is the most common advanced control technique used. Often the feedforward signal is a flow or speed for ratio control that is corrected by a process PID (e.g. temperature, pH, or composition)

• Blend composition control - additive/feed (flow/flow) ratio • Column temperature control - distillate/feed, reflux/feed, stm/feed, &

bttms/feed (flow/flow) ratio • Combustion temperature control - air/fuel (flow/flow) ratio • Drum level control - feedwater/steam (flow/flow) ratio • Extruder quality control - extruder/mixer (power/power) ratio • Heat exchanger temperature control - coolant/feed (flow/flow) ratio • Neutralizer pH control - reagent/feed (flow/flow) ratio • Reactor reaction rate control - catalyst/reactant (speed/flow) ratio • Reactor composition control - reactant/reactant (flow/flow) ratio • Sheet, web, and film machine direction (MD) gage control - roller/pump

(speed/speed) ratio • Slaker conductivity control - lime/liquor (speed/flow) ratio • Spin line fiber diameter gage control - winder/pump (speed/speed) ratio

Feedforward Applications 1

Feedforward Applications 2

Feedforward is most effective if the loop deadtime is large, disturbance speed is fast & size is large, feedforward gain is known, feedforward measurement & dynamic compensation are accurate

Dynamic compensation is used so the feedforward signal arrives at same point at same time in process as upset

– Compensation of feedforward delay > feedback delay is not possible Feedback correction is essential in industrial processes

– While technically, the correction should be a multiplier for a change in slope and a bias for a change in the intercept in a plot of the manipulated variable versus independent variable (independent from this loop but possibly set by another PID or MPC), a multiplier creates scaling problems for the user, a multiplier introduces a nonlinearity in vessels and columns (non plug flow equipment), and bias errors are bigger than span errors in measurements. For these and other reasons the correction of most feedforward signals is done via a bias

– Correction must have enough positive & negative range for worst case

Feedforward gain can be computed from a material or energy balance & explored for different setpoints and conditions from a plot of the controlled variable (e.g. composition, conductivity, pH, temperature, or gage) vs. ratio of manipulated to independent variable (e.g. feed) but is often based on operating experience

– For concentration and pH control, the flow/flow ratio is valid if the changes in the composition of both the manipulated and feed flow are negligible.

– For column and reactor temperature control, the flow/flow ratio is valid if the changes in the composition and temperature of both the manipulated and feed flow are negligible.

– For reactor reaction rate control, the speed/flow is valid if changes in catalyst quality and void fraction and reactant composition are negligible.

– For heat exchanger control, the flow/flow ratio is valid if changes in temperatures of coolant and feed flow are negligible.

– For reactor temperature control, the flow/flow ratio is valid if changes in temperatures of coolant and feed flow are negligible.

– For slaker conductivity (effective alkali) control, the speed/flow ratio is valid if changes in lime quality, void fraction, and liquor composition are negligible.

– For spin or sheet line gage control, the speed/speed ratio is valid only if changes in the pump pressure and the polymer melt quality are negligible.

Feedforward Applications 3

Feedforward gain is a ratio for most load upsets Feedforward gain is inverse of open loop gain for SP feedforward

– open loop gain is dimensionless product of manipulated variable gain, process variable gain, and measurement variable gain

Feedforward action is in same direction as feedback action for upset but is in opposite of control action for SP feedforward

Feedforward delay & lag adjusted to match delay & lag, respectively in upset path so feedforward correction does not arrive too soon

Feedforward lead is adjusted to compensate for lag in manipulated variable path so the feedforward correction does not arrive too late

The actual and desired feedforward ratio should be displayed along with the bias correction by the process PID

Feedforward Applications 4

Integral Deadband

Will stop limit cycles from deadband and backlash – Reduces valve packing, trim, & seal wear and piston o-ring wear

IDEADBAND setting must be greater than largest limit cycle PV excursion on either side of setpoint

For integrating process or stick-slip or resolution limit – Integral deadband must be set in every PID – Integral deadband must be set in DVC when integral enabled

For self-regulating process & backlash (deadband) – Integral deadband does not have to be set in single loop PID if DVC has

integral deadband when integral enabled – Integral deadband must be set in primary PID for cascade control

Limit cycle amplitude is highly variable – Backlash & stick-slip varies with position and age – Process gain varies with output, PV, and time

Better solution is PIDPlus with threshold sensitivity limit – Threshold sensitivity limit screens out noise as not valid PV update

Nonlinear Gain

Used to reduce cycling around SP from hi process gain (7 pH)

Used to ignore noise at SP Used to reduce interactions Used in surge tank level control Better solution is adaptive tuner

and signal characterizer

Output Tracking for SP Response

“Head-Start” logic for startup & batch SP changes: – For SP change PID tracks best/last startup or batch final

settling value for best/last rise time less total loop deadtime – Closed loop time constant is open loop time constant (λf =1) – Not as fast as Bang-Bang (PID OUT is not at output limit)

“Bang-Bang” logic for startup & batch SP changes: – For SP change PID tracks output limit until the predicted PV

one deadtime into future gets within a deadband of setpoint, the output is then set at best/last startup or batch final settling value for one deadtime

– Implementation uses simple DT block (loop deadtime) to create an old PV subtracted from the new PV to give a delta PV that is added to new PV to create a PV one deadtime into future

– Works best on slow batch and integrating processes

Output Tracking for Protection 1

“Open Loop Backup” to prevent compressor surge: – Once a compressor gets into surge, cycles are so fast & large

that feedback control can not get compressor out of surge – When compressor flow drops below surge SP or a precipitous

drop occurs in flow, PID tracks an output that provides a flow large enough to compensate for the loss in downstream flow for a time larger than the loop deadtime plus the surge period.

“Kicker” to prevent RCRA violation: – An excursion < 2 pH or > 12 pH for even a few sec can be a

recordable RCRA violation regardless of downstream volume – When an inline pH system PV approaches the RCRA pH limit

the PID tracks an incremental output (e.g. 0.25% per sec) opening the reagent valve until the pH sufficiently backs away

“Kicker” for evaporator conductivity

AO SP_Rate_DN and SP_RATE_UP used to insure fast getaway and slow approach

Output Tracking for Protection 2

Output Tracking for Protection 3

Feedback Action

Open Loop Backup

Output Tracking for Protection 4

Mixer

Attenuation Tank

AY

AT

middle selector

AY splitter

AT

FT

FT

AT

AY

AT AT AT

AY

AT AT AT

Mixer

AY

FT

Stage 2 Stage 1

middle selector

Waste middle selector RCAS RCAS

splitter

AY Filter

AY ROUT Kicker AC-1 AC-2

MPC-2 MPC-1

RCRA pH Kicker

Optimization of pH filter and kicker increment saved $50K in reagent costs

Evaporator Conductivity Kicker

Conductivity spike

WBL Flow Kicker

Setpoint Filter

PID SP filter reduces overshoot enabling fast tuning – Setpoint filter time set equal reset time

PID SP filter coordinates timing of flow ratio control – Simultaneous changes in feeds for blending and reactions – Consistent closed loop response for model predictive control

PID SP filter sets closed loop time constant PID SP filter in secondary loop slows down cascade

control system rejection of primary loop disturbances – Secondary loop must be > 4x faster than primary loop

Primary PID must have dynamic reset limit enabled

Setpoint Rate Limits

AO & PID SP rate limits minimize disruption while protecting equipment and optimizing processes – surge valve fast opening and slow closing – VPC fast recovery for upset and slow approach to optimum

AO SP rate limits minimize interaction between loops – Less important loops are made 10x slower than critical loops

PID driving AO SP or secondary PID SP rate limit must have dynamic reset limit enabled

PIDPlus Features 1

Positive feedback implementation of reset with external-reset feedback (dynamic reset limit)

Immediate response to a setpoint change or feedforward signal or mode change

Suspension of integral action until change in PV

Integral action is the exponential response of the positive feedback filter to the change in controller output for the time interval since last update

Derivative action is the PV or error change divided by the time interval since the last update multiplied by the gain and rate time

PID integral mode is restructured to provide integral action to match the process response in the elapsed time (reset time set equal to process time constant)

PID derivative mode is modified to compute a rate of change over the elapsed time from the last new measurement value

PID reset and rate action are only computed when there is a new value

If transmitter damping is set to make noise amplitude less than communication trigger level, valve packing and battery life is dramatically improved

Enhancement compensates for measurement sample time suppressing oscillations and enabling a smooth recovery from a loss in communications further extending packing -battery life

+

+

+

+

Elapsed Time

Elapsed Time

TD

Kc

Kc

TD

http://www2.emersonprocess.com/siteadmincenter/PM%20DeltaV%20Documents/ Whitepapers/WP_DeltaV%20PID%20Enhancements%20for%20Wireless.pdf

Link to PIDPlus White Paper

PIDPlus Features 2

PIDPlus Flow Setpoint Response

Traditional PID Sensor PV

Enhanced PID (PIDPlus) Sensor PV

Traditional PID Wireless PV

Enhanced PID (PIDPlus)

Wireless PV

Traditional PID Sensor PV

Enhanced PID (PIDPlus) Sensor PV

PIDPlus Flow Load Response

Enhanced PID (PIDPlus) Sensor PV

Traditional PID Sensor PV

PIDPlus Flow Failure Response

Enhanced PID (PIDPlus) Sensor PV

Traditional PID Sensor PV

PIDPlus pH Setpoint Response

Traditional PID Sensor PV

Enhanced PID (PIDPlus) Sensor PV

PIDPlus pH Load Response

Traditional PID Sensor PV

Enhanced PID (PIDPlus) Sensor PV

PIDPlus pH Failure Response

PID PV

PID Output

Enhanced PID Traditional PID

Limit Cycles from Valve Stick-Slip

PIDPlus Stops Limit Cycles

The PID enhancement for wireless (PIDPlus) offers an improvement wherever there is an update time in the loop. In the broadest sense, an update time can range from seconds (wireless updates and valve or measurement sensitivity limits) to hours (failures in communication, valve, or measurement). Some of the sources of update time are: – Wireless update time for periodic reporting (default update rate) – Wireless measurement trigger level for exception reporting (trigger level) – Wireless communication failure – Broken pH electrode glass or lead wires (failure point is about 7 pH) – Valve with backlash (deadband) and stick-slip (resolution) – Operating at split range point (no response & abrupt response discontinuity) – Valve with solids, high temperature, or sticky fluid (plugging and seizing) – Plugged impulse lines – Analyzer sample, analysis cycle, and multiplex time – Analyzer resolution and threshold sensitivity limit

To completely stop a valve limit cycle from backlash or stick-slip, measurement updates must not occur due to noise

PIDPlus Benefits Beyond Wireless 1

Enhanced PID executes for a change in setpoint, feedforward, or remote output to provide an immediate reaction based on PID structure

The improvement in control by the enhanced PID is most noticeable as the update time becomes much larger than the 63% process response time (defined in the white paper as the sum of the process deadtime and time constant). When the update time becomes 4 times larger than this 63% process response time ( 98% response time frequently cited in the literature), the feedforward and controller gains can be set to provide a complete correction for changes in the measurement and setpoint. – Helps ignore inverse response and errors in feedforward timing – Helps ignore discontinuity (e.g. steam shock) at split range point – Helps extend packing life by reducing oscillations and hence valve travel

Since enhanced PID can be set to execute only upon a significant change in user valve position, this PID as a valve position controller offers less interaction and cycling for optimization of unit operations by increasing reactor feed, column feed or increasing refrigeration unit temperature, or decreasing compressor pressure till feed, vent, coolant, and/or steam, valves are at maximum good throttle position.

http://www.modelingandcontrol.com/2010/08/wireless_pid_benefits_extend_t.html http://www.modelingandcontrol.com/2010/10/enhanced_pid_for_wireless_elim.html

http://www.modelingandcontrol.com/2010/11/a_delay_of_any_sorts.html

Website entries on Enhanced PID (PIDPlus) Benefits

PIDPlus Benefits Beyond Wireless 2

Key Features for VPC

Feature Function Advantage 1 Advantage 2

Direction Velocity Limits

Limit VPC Action Speed Based on Direction

Prevent Running Out of Valve

Minimize Disruption to Process

Dynamic Reset Limit

Limit VPC Action Speed to Process Response

Direction Velocity Limits

Prevent Burst of Oscillations

Adaptive Tuning Automatically Identify and Schedule Tuning

Eliminate Manual Tuning

Compensation of Nonlinearity

Feedforward Preemptively Set VPC Out for Upset

Prevent Running Out of Valve

Minimize Disruption

Enhanced PID (PIDPlus) Suspend Integral Action until PV Update

Eliminate Limit Cycles from Stiction &

Backlash

Minimize Oscillations from Interaction &

Delay

VPC for Small and Big Valve

Small valve provides precision and big valve gives rangeability

Examples of Optimization by VPC Optimization VPC PID PV VPC PID SP VPC PID Out

Minimize Prime Mover Energy

Reactor Feed Flow PID Out

Max Throttle Position Compressor or Pump Pressure SP

Minimize Boiler Fuel Cost

Steam Flow PID Out Max Throttle Position Boiler Pressure SP

Minimize Boiler Fuel Cost

Equipment Temperature PID Out

Max Throttle Position Boiler Pressure SP

Minimize Chiller or CTW Energy

Equipment Temperature PID Out

Max Throttle Position Chiller or CTW Temperature SP

Minimize Purchased Reagent or Fuel Cost

Purchased Reagent or Fuel Flow PID Out

Min Throttle Position

Waste Reagent Or Fuel Flow SP

Minimize Total Reagent Use

Final Neutralization Stage pH PID Out

Min Throttle Position

First Neutralization Stage pH PID SP

Maximize Reactor Production Rate

Reactor or Condenser Temperature PID Out

Max Throttle Position Feed Flow or Reaction Temperature SP

Maximize Reactor Production Rate

Reactor Vent Pressure PID Out

Max Throttle Position Feed Flow or Reaction Temperature SP

Maximize Column Production Rate

Reboiler or Condenser Flow PID Out

Max Throttle Position Feed Flow or Column Pressure SP

Maximize Ratio or Feedforward Accuracy

Process Feedback Correction PID Out

50% (Zero Correction)

Flow Ratio or Feedforward Gain

54

Liquid Reactants (Jacket CTW) Liquid Product Optimization

TT 1-4

TC 1-3

TC 1-4

AT 1-6

LY 1-8

FY 1-6

FT 1-2

FC 1-2

reactant A

reactant B

CAS

residence time calc

CAS

ratio calc

AC 1-6

makeup

return

LY 1-8

FY 1-6

reactant A

reactant B

residence time calc LT

1-8 TT 1-3

LC 1-8

CAS

ratio calc

product

vent FT 1-1

FC 1-1

FC 1-1 CAS

ZC1-4 OUT

ZC 1-4

FC 1-7

FT 1-7

PT 1-5

PC 1-5

FT 1-5

CTW

ZC1-4 is an enhanced PID VPC

Valve position controller (VPC) setpoint is the maximum throttle position. The VPC should turn off integral action to prevent interaction and limit cycles. The correction for a valve position less than setpoint should be slow to provide a slow approach to optimum. The correction for a valve position greater than setpoint must be fast to provide a fast getaway from the point of loss of control. Directional velocity limits in AO with dynamic reset limit in an enhanced PID that tempers integral action can achieve these optimization objectives.

55

Liquid Reactants (Jacket CTW) Gas & Liquid Products Optimization

TT 1-4

TC 1-4

AT 1-6

LY 1-8

FY 1-6

FT 1-2

FC 1-2

reactant A

reactant B

residence time calc

CAS

ratio calc

AC 1-6

makeup

return

LY 1-8

FY 1-6

reactant A

reactant B

CAS

residence time calc LT

1-8

LC 1-8

CAS

ratio calc

product

FT 1-1

FC 1-1

FC 1-7

FT 1-7

CAS

TC 1-3

TT 1-3

product

PC 1-5

FT 1-5

W

PT 1-5

TT 1-10

TC 1-10

ZC 1-4

ZC 1-10

ZC 1-5

ZY 1-1

FC1-1 CAS

ZY1-1 OUT

low signal selector

ZC-10 OUT

ZC-4 OUT

ZC-5 OUT

ZY-1 IN1

ZY-1 IN2

ZY-1 IN3

CTW

ZC1-4, ZC-5, & ZC-10 are enhanced PID VPC

56 56

Innovative PID System to Optimize Ethanol Yield and Carbon Footprint

AT 1- 4

AC 1- 4

DC 2- 4

SC 1-4

FT 1- 5

FC 1- 5

AY 1- 4

Corn

NIR-T

Production Rate Enhanced PID

DT 2- 4

Slurry Solids Enhanced PID

DX 2- 4

Feedforward

FT 1- 6

FC 1- 6

Backset Recycle

Dilution Water

XC 1- 4

XY 1- 4

Average Fermentation Time Enhanced PID

Fermentable Starch Correction

Slurry Tank 1

Slurry Tank 2

Coriolis Meter

setpoint

DY 2- 4

Lag and Delay

RCAS

Predicted Fermentable Starch

Business Results Achieved Batch cycle time & startup time reduction

– PID structures 1 & 2, SP feedforward, & output tracking for Bang-Bang logic to speed-up SP response

Valve life cycle cost reduction – Integral deadband & PIDPlus to reduce valve dither

Equipment and environmental protection – Dynamic reset limit & AO SP rate limits to ensure slow approach to

normal operating point & fast getaway for abnormal conditions – Output tracking for open loop backup & kicker for fast recovery

Process variability reduction – Dynamic reset limit & PID SP filter & rate limits for max upset rejection

with min SP overshoot & consistent blending & parallel train response – Dynamic reset limit & AO SP rate limits for interaction reduction – PIDPlus for smooth analyzer & wireless control & for failure recovery – PIDPlus for robustness in feedforward timing correction

Process efficiency and capacity improvement – PIDPlus for more effective valve position control – PIDPlus for more effective analyzer & batch end point control – Dynamic reset limit & SP rate limits to ensure slow approach to

optimum operating point & fast getaway for abnormal conditions

Summary

The role of the PID is expanding from basic control into advanced regulatory control with the ability to provide quick optimization solutions by innovative use of key PID features, such as dynamic reset limit & PIDPlus

Tuning is simplified in that the same tuning used for disturbance rejection can be used for SP response, coordination of loops, optimization of loops, and loops where significant measurement update delay has been introduced by wireless devices & analyzers

Feedback? Questions?

Where To Get More Information

Greg McMillan, “What is the Key PID Feature for Basic and Advanced Control”, Control Talk Blog, 4-26-2012

– http://community.controlglobal.com/content/what-key-pid-feature-basic-and-advanced-control

Greg McMillan and Hector Torres, “Effective use of Key PID features”, ISA Automation Week 2012

Greg McMillan and Hunter Vegas, 101 Tips for a Successful Automation Career, ISA, 2012