Interactive Exploration of Process Control Improvement · Interactive Exploration of Process Control Improvement Jack Ahlers ... Reflux Drum Lc, Vc_out Reflux L_R Distillate product

Interactive Exploration of Process Control Improvement

Jack Ahlers - Process Control Specialist

Greg McMillan - Principle Consultant

Presenters

Jack Ahlers

Greg McMillan

Introduction

An online process control lab is used to provide an interactive

exploration and quantification of process control improvements to

get the most out of your PID

Demos of PID solutions via online process control labs show how

to reduce process variability and improve setpoint response

– Dynamic Reset solution for slow valves and secondary loops

– PIDPlus solution for

• Wireless Measurements

• Failed Measurements

• Analyzers with Sample Systems

• Valve Backlash and Stick-slip

– Smart Bang-Bang Logic solution for batch and startup sequences

– Deadtime Compensation solution for high process deadtime

Online Process Control Labs -Free Access to Virtual Plants

Visit http://www.processcontrollab.com/to Create Valuable New Skills

Free State of the Art Virtual Plant

Not an emulation but a DCS (SimulatePro)

Independent Interactive Study

Structural Changes “On the Fly”

Advanced PID Options and Tuning Tools

Enough variety of valve, measurement, and process dynamics to study 90% of the process industry’s control applications

Learn in 10 minutes rather than 10 years

Online Performance Metrics

Standard Operator Graphics & Historian

Control Room Type Environment

No Modeling Expertise Needed

No Configuration Expertise Needed

Rapid Risk-Free Plant Experimentation

Deeper Understanding of Concepts

Process Control Improvement Demos

Sample Lessons (Recorded Deminars)

http://www.processcontrollab.com/

The Opportunities Beyond Operator Training Systems

Dynamic simulations offer the opportunity to explore, quantify, demonstrate, detail, and prototype process control improvements (PCI)

However, the investment in software and time to learn and develop simulations typically limits the creation of models to specialists who have significant simulation and DCS expertise.

Process deadtime, measurement dynamics, and valve response is often not modeled (not understood by traditional process simulation software suppliers)

The emulation of the basic and advanced control capability in a DCS by process simulation software is unrealistic

What is needed is a virtual plant that uses the actual DCS with all of its capability and uses dynamics of all parts of the process and automation systems in a friendly control room environment by the use of the DCS operator interface

The virtual plant should be useable by any one who wants to learn the best of the practical control technologies for the process industry and to find, demonstrate, estimate, and convince people of the benefits of process control improvement

– Automation Engineers

– Local Business Partners

– Process Engineers

– Students

– System Integrators

– Suppliers

PCI and OTS Virtual Plants

Virtual

Process

Virtual

Sensors

Virtual

Valves

Virtual

DCS

Virtual

Process

Virtual

Sensors

Virtual

Valves

Virtual

I/OActual

DCS

Traditional

Process

Simulators

MiMiC

PCI

MiMiC

OTS

DeltaV

SimulatePro

DeltaV

ProPlus

Virtual Plant Essentials

Feed 1

Feed 2

Condenser

Cooling water Fcw

Reflux Drum

Lc, Vc_out

Reflux L_R

Distillate product L_D

CW Out

V_DA_VD1

A_Vlv1

Reboiler

A_v

L_B + V_B

V_B

Buttom product L_B

Heating steam

HE condensate

Side withdraw 2

Side withdraw 1

Heavy liquid L_HvLiq

Vnt

V_D1

DeltaV Simulate Product Family

MiMiC Simulation Software

Top Ten Things You Don’t Want to Hear in a Project Definition Meeting

(10) I don’t want any smart instrumentation talking back to me

(9) Let’s study each loop to see if the valve really needs a positioner

(8) Lets slap an actuator on our piping valves and use them for

control valves

(7) We just need to make sure the control valve spec requires the

tightest shutoff

(6) What is the big deal about process control, we just have to set the

flow per the PFD

Top Ten Things You Don’t Want to Hear in a Project Definition Meeting

(5) Cascade control seems awfully complex

(4) The operators can tune the loops

(3) Let’s do the project for half the money in half the time

(2) Let’s go with packaged equipment and let the equipment supplier

select and design the automation system

(1) Let’s go out for bids and have purchasing pick the best deal

Online Process Control Labs - Demo

Objective – Show access to virtual plant

Activities:– Go to http://www.processcontrollab.com/

– Look at Overview (PDF File)

– Look at How to Connect screen

– Show Request Access to a Virtual Plant (VP)

– Make a Remote Desktop connection to the assigned VP

– Click on DeltaV Operate

– Put all of the Process Control Labs in the Run mode

– Click on Trend Chart icon and open up charts for the Labs

– On Main DeltaV Operate screen discuss the Restore button

– In the Process Control Lab website show Help screen

– In the Process Control Lab website show Instructions screen

– Minimize screens and in FlexLock select Logoff Window


Unifying Concepts

“It is all about management of change” – Intentional change (setpoints)

– Unintentional change (disturbances)

– 90% of process control improvements involve the following concepts:• Delay

• Speed

• Gain

• Sensitivity-Resolution

• Backlash-Deadband

• Nonlinearity

• Noise

• Oscillations

• Resonance

• Attenuation

• Optimum

We will cover delay, speed, and gain since these are most prevalent limiting concepts

Checkout Deminar #9 “Process Control Improvement Primer” for other concepts

http://www.modelingandcontrol.com/2010/09/review_of_deminar_9_-_process.html




Delay “Without deadtime I would be out of a job” Fundamentals

– A more descriptive name would be total loop deadtime. The loop deadtime is the amount of time for the start of a change to completely circle the control loop and end up at the point of origin. For example, an unmeasured disturbance cannot be corrected until the change is seen and the correction arrives in the process at the same point as the disturbance.

– While process deadtime offers a continuous train of values whereas digital devices and analyzers offer non continuous data values at discrete intervals, these delays add a phase shift and increase the ultimate period (decrease natural frequency) like process deadtime.

Goals– Minimize delay (the loop cannot do anything until it sees and enacts change)

Sources– Pure delay from deadtimes and discontinuous updates

• Piping, duct, plug flow reactor, conveyor, extruder, spin-line, and sheet transportation delays• Digital devices - scan, update, reporting, and execution times (0.5*DT)• Analyzers - sample processing and analysis cycle time (1.5*DT)• Sensitivity-resolution limits• Backlash-deadband

– Equivalent delay from lags• Mixing • Column trays • Heat transfer surfaces• Thermowells• Electrodes • Transmitter damping and signal filter settings

Speed (Rate of Change)

“Speed kills - (high speed processes and disturbances and low speed control systems can kill performance)”

Fundamentals– The rate of change in 4 deadtime intervals is most important. By the end of 4

deadtimes, the control loop should have completed most of its correction. Thus, the short cut tuning method (Deminar #6) is consistent with performance objectives.

Goals– Make control systems faster and make processes and disturbances slower

Sources– Control system

• PID tuning settings (gain, reset, and rate)

• Slewing rate of control valves and velocity limits of variable speed drives

– Disturbances• Steps - Batch operations, on-off control, manual actions, SIS, startups, and shutdowns

• Oscillations - limit cycles, interactions, and excessively fast PID tuning

• Ramps - reset action in PID

– Process• Mixing in volumes due to agitation, boiling, mass transfer, diffusion, and migration

Gain

“All is lost if nothing is gained” Fundamentals

– Gain is the change in output for a change in input to any part of the control system. Thus there is a gain for the PID, valve, disturbance, process, and measurement. Knowing the disturbance gain (e.g. change in manipulated flow per change in disturbance) is important for sizing valves and feedforward control.

Goals– Maximize control system gains (maximize control system reaction to change) and

minimize process and disturbance gains (minimize process reaction to change).

Sources– PID controller gain – Inferential measurements (e.g. temperature change for composition change in

distillation column) – Slope of control valve or variable speed drive installed characteristic (inherent

characteristic & system loss curve)– Measurement calibration (100% / span). Important where accuracy is % of span– Process design– Attenuation by volumes (can be estimated)– Attenuation by PID (transfer of variability from controlled to manipulated variables)

Time (seconds)

% Controlled Variable (CV)

or

% Controller Output (CO)

DCO

DCV

qo tp2

Kp = DCV / DCO

0.63*DCV

CO

CV

Self-regulating process

open loop

negative feedback time constant

Self-regulating process gain (%/%)

Response to change in controller output with controller in manual

observed

total loop

deadtime

toor

Maximum speed

in 4 deadtimes

is critical speed

Self-Regulating Process Open Loop Response

Time (seconds)qo

Ki = { [ CV2 / Dt2 ] - [ CV1 / Dt1 ] } / DCO

DCO

ramp rate is

DCV1 / Dt1

ramp rate is

DCV2 / Dt2

CO

CV

Integrating process gain (%/sec/%)

Response to change in controller output with controller in manual% Controlled Variable (CV)

or


observed

total loop

deadtime

Maximum speed

in 4 deadtimes

is critical speed

Integrating Process Open Loop Response

Response to change in controller output with controller in manual

qo t’p2

Noise Band

Acceleration

DCV

DCO

1.72*DCV

Kp = DCV / DCO

Runaway process gain (%/%)

% Controlled Variable (CV)

or


Time (seconds)observed

total loop

deadtimerunaway process

open loop

positive feedback time constant

For safety reasons, tests are

terminated after 4 deadtimes

t’oor

Maximum speed

in 4 deadtimes

is critical speed

Runaway Process Open Loop Response

tp1 qp2 tp2Kpvqp1

tc1 tm2 qm2 tm1 qm1Kcvqctc2

Kc Ti Td

Valve Process

Controller Measurement

Kmvtvqv

KLtLqL

Load Upset

DCV

DCO

DMVDPV

PID

Delay Lag

Delay Delay Delay

Delay

Delay

Delay

Lag Lag Lag

LagLagLag

Lag

Gain

Gain

Gain

Gain

Local

Set Point

DDV

First Order Approximation: qo @ qv + qp1 + qp2 +

qm1 + qm2 + qc + tv + tp1 + tm1 + tm2 + tc1 + tc2

%

%

%

Delay => Dead Time

Lag =>Time Constant

Ki = Kmv * (Kpv / tp2 ) * Kcv

100% / span

Loop Block Diagram(First Order Approximation)

DCO = change in controller output (%) DCV = change in controlled variable (%) DDV = change in disturbance variable (%) Eo = open loop error (%) - step disturbance EL = load (%) - lagged disturbance Kc = controller gain (dimensionless) Ki = integrating process gain (%/sec/% or 1/sec) Kp = process gain (dimensionless) also known as open loop gain Rv = slew rate of control valve (%/sec) MV = manipulated variable (engineering units) PV = process variable (engineering units) Dt = change in time (sec) Dtx = PID execution time (sec) qo = total loop dead time (sec) tf = filter time constant (sec) tm = measurement time constant (sec) tp2 = primary (large) self-regulating process time constant (sec) t’p2 = primary (large) runaway process time constant (sec) tp1 = secondary (small) process time constant (sec) Ti = integral (reset) time setting (sec/repeat) Td = derivative (rate) time setting (sec) To = oscillation period (sec) l = Lambda (closed loop time constant or arrest time) (sec)

Nomenclature

Practical Limit to Loop Performance

o

cp

x EKK

E **+

=)1(

1

o

cp

fxi

i EKK

tTE *

*

+D+=

t

Peak error decreases as the controller gain increases but is essentially the

open loop error for systems when total deadtime >> process time constant

Integrated error decreases as the controller gain increases and reset time decreases

but is essentially the open loop error multiplied by the reset time plus signal

delays and lags for systems when total deadtime >> process time constant

Peak and integrated errors cannot be better than ultimate limit - The errors predicted

by these equations for the PIDPlus and deadtime compensators cannot be better

than the ultimate limit set by the loop deadtime and process time constant

i

c

o

v

T

K

E

R

Valve slew rate (Rv)

limits effective

speed of tuning

Ultimate Limit to Loop Performance

o

po

ox EE *

+=

)( tq

q

o

po

oi EE *

+=

)(

2

tq

q

Peak error is proportional to the ratio of loop deadtime to 63% response time

Integrated error is proportional to the ratio of loop deadtime squared to 63% response time

For a sensor lag (e.g. electrode or thermowell lag) or signal filter that is much larger

than the process time constant, the unfiltered actual process variable error can be

found from the equation for attenuation

The PIDPlus enhancement for measurement delay and the

addition of a DT block for compensation of process deadtime

can achieve the ultimate limits to loop performance !

Peak and Integrated Error Check List

Disturbance Speed and Attenuation

oL EeE Lo *-=-

)1(/tq

f

oof

TAA

t *=

2*

Effect of load disturbance lag (tL) can be estimated by replacing the open loop error

with the exponential response of the disturbance during the loop deadtime

The attenuation of oscillations van be estimated from the expression of the Bode plot

equation for the attenuation of oscillations slower than the break frequency where (tf) is

the filter time constant, electrode or thermowell lag, or a mixed volume residence time

For biological processes the load disturbance lag (tL) can be so slow (e.g. days),

temperature control is a non-issue for a well designed coolant system

Implied Deadtime from Slow Tuning

)(5.0 oi qlq +*=

Slow tuning (large Lambda) creates an implied deadtime where the loop performs

about the same as a loop with fast tuning and an actual deadtime equal to the

implied deadtime (qi)

Money spent on improving measurement and process dynamics

(e.g. reducing measurement delays and process deadtimes)

will be waste if the controller is not tuned faster to take

advantage of the faster dynamics

You can prove most any point you want to make in a comparison

of control system performance, by how you tune the PID.

inventors of special algorithms as alternatives to the PID

naturally tend to tune the PID to prove their case.

“Advanced Control Algorithms; Beware of False Prophecies”

http://www.modelingandcontrol.com/FunnyThing/

http://www.modelingandcontrol.com/FunnyThing/

Effect of Implied Deadtime onAllowable Digital or Analyzer Delay

In this self-regulating process the original process delay (dead time) was 10 sec.

Lambda was 20 sec and the sample time was set at 0, 5, 10, 20, 30, and 80 sec (Loops 1 - 6)

The loop integrated error increased slightly by 1%*sec for a sample time of 10 sec which corresponded to a

total deadtime (original process deadtime + 1/2 sample time) equal to the implied deadtime of 15 seconds.

http://www.modelingandcontrol.com/repository/AdvancedApplicationNote005.pdf

sample time = 0 sec

sample time = 5 sec

sample time = 10 sec




http://www.modelingandcontrol.com/repository/AdvancedApplicationNote005.pdf

Fastest Practical PID Tuning Settings(Practical Limit to Loop Performance)

op

p

cK

Kq

t

**=

24.0

oiT q*= 2 1d pT t=

For runaway processes:

For self-regulating processes:

oi

cK

Kq*

*=1

5.0oiT q*= 4 1d pT t=

oi

cK

Kq*

*=1

6.0

oiT q*= 40 1d 2 pT t*=

For integrating processes:

op

p

cK

Kq

t

**=

2'6.0

oi

cK

Kq*

*=1

4.0

Near integrator (tp2 >> qo):

oiT q*= 5.0

Near integrator (t’p2 >> qo):

Deadtime dominant (tp2 << qo):

0d =T

Effect of Tuning Speed Oscillatory Disturbance

1

Ultimate

Period

1

1Faster

Tuning

Log of Ratio of

closed loop amplitude

to open loop amplitude

Log of ratio of

disturbance period

to ultimate period

no attenuation

of disturbances

resonance (amplification)

of disturbances

amplitude ratio is

proportional to ratio of

break frequency lag to

disturbance period

1

no better than manual worse than manual improving control

Fast Valve and Fast Cascade Demo

Objective – Show access to cascade loop lab setup and how to make load upsets to see response for fast valve and fast cascade

Activities:– Show access to Cascade Loop Lab02 user interface

– Show access to PID faceplate and detail

– Show access to “Process History View” trend chart

– Click on secondary PID faceplate and put secondary PID in AUTO mode

– Make load change to show secondary response by putting secondary PIDmomentarily in manual and changing its output (e.g. 50% to 60%)

– Click on any block in block diagram to access Detail for parameters that will be changed in these demos via tabs for PID, process, and valve

– Put secondary PID in CAS mode and click on primary PID faceplate

– Make load change to show cascade response by putting primary PID momentarily in manual and changing its PID output (e.g. 50% to 60%)

Note: AC1-1 is primary PID and AC1-2 is secondary PID

Volume Booster with Integral Bypass(Furnace Pressure and Surge Control)

Signal from

Positioner

Air Supply from

Filter-Regulator

Air Loading

to Actuator

Adjustable Bypass

Needle Valve

Booster and Positioner Setup(Furnace Pressure and Surge Control)

Port A

Port B

Supply

ZZ

ZZ

ZZ

Z

Control Signal

Digital Valve Controller

Must be functionally

tested

before commissioning!

1:1

Bypass

Volume

Booster

Open bypass just

enough to ensure

a non-oscillatory

fast response

Air Supply

High Capacity

Filter Regulator

Increase air line size

Increase connection size

Terminal Box

Slow Valve Demo

Objective – Show response of secondary PID to slow valve for

small and large upsets

Activities:

– First look at Demo for fast valve and fast secondary loop

– Click on any block in block diagram – Click on Control Valve tab

– Change Slew Inc and Slew Dec of valve from 100%/sec to 1%/sec

– Click on secondary PID faceplate and put secondary PID in AUTO mode

– Make small load change to show response by putting secondary PID

momentarily in manual and changing its PID output (e.g. 50% to 52%)

– Make large load change to show response by putting secondary PID


Ramping Response of Actuator for a Large Step or a Large Actuator

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4 5 6 7 8 9 10

Time (sec)

Str

oke

(%

)

Multiply time by 10 for large actuator

without volume booster

Exponential Response of Actuator for a Small Step or a Small Actuator

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 1 2 3 4 5 6 7 8 9 10

S

tro

ke

(%

)

Time (sec)

Slow Valve DemoDynamic Reset Limit Enabled

Objective – Show response of secondary PID with Dynamic

Reset Limit to slow valve

Activities:

– First look at Demo for slow valve

– Click on any block in block diagram – Click on PID tab

– Enable Dynamic Reset Limit for secondary PID

– Make large load change to show response by putting secondary PID


Positive Feedback Implementation of Integral Mode with Dynamic Reset Limit

S

*

SP

b

D proportional

derivative

*

Gain

*

** *

Rate

D

D

g

CO

filter

filter

CV filter

Filter Time =

a * Rate Time

S

filter

Filter Time =

Reset Time

ER is external reset

(e.g. secondary PV)

Dynamic Reset Limit

ER

Positive

Feedback

Slow Secondary Loop Demo

Objective – Show response of self-regulating primary PID to slow

secondary loop for small and large upsets

Activities:

– First look at Demo with dynamic reset limit for slow valve

– Click on any block in block diagram – Click on Control Valve tab

– Change valve Slew Inc and Slew Dec from 1%/sec to 100%/sec

– Click on PID tab and disable Dynamic Reset Limit for secondary PID

– Click on Process tab and increase secondary Lag 2 Inc and Lag 2 Dec from

2 to 10 sec

– On secondary PID detail, increase reset time from 2 to 10 sec

– Put secondary PID is in CAS mode

– Click on primary PID faceplate and detail

– Make small load change to show response by putting primary PID


– Make large load change to show response by putting primary PID


Cascade Control Benefit (self-regulating process)

qi / qo= 0.6

(ti / to)

qi / qo= 1.0

ti = inner loop process time constant

to = outer loop process time constant

qi = inner loop process deadtime

qo = outer loop process deadtime

Improvement significantly greater

(ratio of peak errors much smaller)

for integrating and runaway

primary processes

Slow Secondary Loop DemoDynamic Reset Limit Enabled

Objective – Show response of self-regulating primary PID with

Dynamic Reset Limit to slow secondary loop

Activities:

– First look at Demo for slow secondary PID

– Click on any block in block diagram – Click on PID tab

– Enable Dynamic Reset Limit for primary PID

– Make large load change to show response by putting primary PID


PIDPlus Solution - Algorithm

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 sensitivity limit, 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

PIDPlus Benefit DemoFast Secondary (Flow)

Objective – Show how PIDPlus can achieve the ultimate performance limit for a wireless refresh time of 16 sec in a secondary loop (flow)

Activities:– First look at Demo for slow secondary PID with Dynamic Reset Limit enabled

– Put secondary loop in AUTO

– In PID detail, disable Dynamic Reset Limit in secondary and primary PID

– Change secondary setpoint from 50% to 60%

– On Measurement tab Detail set Refresh = 16 sec and Sensitivity = 100% for secondary measurement


– Wait for oscillations to develop

– In PID detail, Enable PIDPlus for secondary loop

– Wait for oscillations to die out


http://www2.emersonprocess.com/siteadmincenter/PM%20DeltaV%20Documents/

Whitepapers/WP_DeltaV%20PID%20Enhancements%20for%20Wireless.pdf

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



Flow Loop Setpoint ResponsePIDPlus versus Traditional PID

Flow Loop Load ResponsePIDPlus versus Traditional PID

Flow Loop Failure ResponsePIDPlus versus Traditional PID

PIDPlus Benefit DemoInline Primary Loop (Static Mixer pH)

Objective – Show how PIDPlus can achieve the ultimate performance limit for wireless refresh time of 60 sec in a primary loop (static mixer pH)

Activities:– First look at Demo for wireless secondary loop with PIDPlus enabled

– Put secondary loop in MAN

– Change secondary loop manual output from 60 to 50%

– Put secondary loop in CAS

– Change primary PID setpoint from 50% to 60%

– Note response with wired primary loop and PIDPlus wireless secondary loop

– In Measurement detail, Set Refresh = 60 sec and Sensitivity = 100% for primary measurement

– Make primary PID setpoint change from 60% to 50%


– In PID detail, enable PIDPlus for primary loop



http://www2.emersonprocess.com/siteadmincenter/PM%20DeltaV%20Documents/

Whitepapers/WP_DeltaV%20PID%20Enhancements%20for%20Wireless.pdf




Static Mixer pH Loop Setpoint ResponsePIDPlus versus Traditional PID

Static Mixer pH Loop Load ResponsePIDPlus versus Traditional PID

Static Mixer pH Loop Failure ResponsePIDPlus versus Traditional PID

PIDPlus Benefit DemoFast Valve Limit Cycle (e.g. Flow)

Objective – Show how PIDPlus can eliminate limit cycles from valve stick-slip

Activities:– First look at Demo for wireless secondary and primary loops with PID

PIDPlus enabled in both the secondary and primary loops

– Put secondary loop in MAN


– In Measurement detail, return to wired measurements (set Refresh = 0 sec and Sensitivity = 0% for both the secondary and primary measurements)

– In PID detail, disable PIDPlus in secondary and primary PID

– In Control Valve detail, set Stick-Slip = 4%


– Put secondary loop in AUTO


– In PID detail, enable PIDPlus in secondary PID


– Change secondary setpoint from 50 to 60%

Smart Bang-Bang Control toReduce Fed-Batch and Startup Time Full Throttle (Smart Bang-Bang) Control - The controller output is stepped

to it output limit to maximize the rate of approach to setpoint and when the projected PV equals the setpoint less a bias, the controller output is repositioned to the final resting value. The output is held at the final resting value for one deadtime. For more details, check out the Control magazine article “Full Throttle Batch and Startup Response.”

http://www.controlglobal.com/articles/2006/096.html– A deadtime (DT) block must be used to compute the rate of change so that new

values of the PV are seen immediately as a change in the rate of approach.

– If the total loop deadtime (qo) is used in the DT block, the projected PV is simply the current PV minus the output of the DT block (DPV) plus the current PV.

• If the PV rate of change (DPV/Dt) is useful for other reasons (e.g. near integrator or true integrating process tuning), then DPV/Dt = DPV/qo can be computed.

– If the process changes during the setpoint response (e.g. reaction or evaporation), the resting value can be captured from the last batch or startup

– If the process changes are negligible during the setpoint response, the resting value can be estimated as:

• PID output just before the setpoint change for an integrating (e.g. batch) process

• PID output just before the setpoint change plus the setpoint change divided by the process gain for a self-regulating (e.g. continuous) process

– For self-regulating processes such as flow with the loop deadtime (qo) approaching or less than the largest process time constant (tp ), the logic is revised to step the PID output immediately to the resting value. The PID output is held at the resting value for the T98 process response time (T98 = qo + 4* tp ).

http://www.controlglobal.com/articles/2006/096.html

Smart Bang-Bang Control Demo

Objective – Show how to reduce batch and startup time by a full

throttle setpoint response (bang-bang control)

Activities:

– Go to Main Display and then select Single Loop Lab01

– Click on PID faceplate and then on its Detail icon (faceplate lower left corner)

– Enter tuning settings: Gain = 1.7, Reset = 210 sec, Rate = 2 sec

– Click on any block in block diagram and then on Process tab detail

– Set primary process Delay = 9 sec, Lag 2 Inc & Lag 2 Dec = 100 sec

– Set primary process Type = Integrating

– Enable setpoint response metrics

– Make setpoint change from 50% to 60%

– Wait for setpoint response to complete and note metrics

– In PID detail, set Bang-Bang Bias = 4%



Setpoint Response Results (Deminar #7)

Structure 3

Rise Time = 8.5 min

Settling Time = 8.5 min

Overshoot = 0%

Structure 1

Rise Time = 1.6 min


Overshoot = 1.7%

Structure 1 + SP FF

Rise Time = 1.2 min


Overshoot = 1.3%

Structure 1 + Bang-Bang

Rise Time = 0.5 min


Overshoot = 0.2%

http://www.screencast.com/users/JimCahill/folders/Deminars/media/6074a326-f7c9-4485-b827-a306515c63c9










Deadtime Compensation Demo

Objective – Show how to achieve ultimate limit for loop performance by process deadtime compensation

Activities:– Go to Main Display and then select Single Loop Lab01

– Click on any block in block diagram and then on Process tab detail

– Set primary process type = Self-Regulating

– Set primary process Delay = 9 sec

– Set primary and secondary Lag 2 Inc & Lag 2 Dec = 1 sec

– Put loop in MAN

– Click on PID faceplate and then on its Detail icon (faceplate lower left corner)


– Set primary process type = Self-Regulating

– Put loop in AUTO

– Enable setpoint response metrics



– In PID Detail, enable Dynamic Reset Limit and set PID Deadtime = 10 sec




Deadtime Compensation Configuration

Insert

deadtime

block

Must enable dynamic reset limit !

Business Results Achieved

A faster setpoint response and load rejection for

improved process capacity and efficiency can be

achieved by the use of:

– Dynamic Reset to prevent the primary loop output from

changing faster than the valve or secondary loop can respond

– PIDPlus (DeltaV v11) to prevent ramp of output from

measurement failure, eliminate spikes in output from

measurement restore, achieve ultimate the performance limit

for a large measurement delay, and stop limit cycles from

measurement sensitivity limit and valve stick-slip or backlash

– Smart Bang-Bang for faster startups of slow processes

– Deadtime compensation to achieve ultimate performance

limit for large well known process deadtime

Summary

Use process control labs for “hands on learning”

Enable dynamic reset for big valves with fast readback of actual valve position and slow secondary loops

Use PIDPlus for wireless measurements, analyzers, and valves or dampers with excessive backlash and stick-slip

Use smart bang-bang composite template library module for faster setpoint response for slow integrating and near-integrating processes (startups and batch ops)

Add a deadtime block to PID external reset BK_CAL and enable dynamic reset limit to compensate for large well known process deadtimes

Questions?

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Instrumentation and Control

Where To Get More Information

Modeling and Control Website http://www.modelingandcontrol.com/

Process Control Lab Website http://www.processcontrollab.com/

“DeltaV Version 11 PID Enhancements for Wireless”, Emerson White Paper, July 2010 http://www2.emersonprocess.com/siteadmincenter/PM%20DeltaV%20Documents/Whitepapers/WP_DeltaV%20PID%20Enhancements%20for%20Wireless.pdf

“Wireless – Overcoming Challenges of PID Control & Analyzer Applications”, InTech, July-Aug 2010 http://www.isa.org/InTechTemplate.cfm?template=/ContentManagement/ContentDisplay.cfm&ContentID=83041

“Adaptive Level Control”, Control, Jan 2010 http://www.controlglobal.com/articles/2010/LevelControl1002.html

“Is Wireless Process Control Ready for Prime Time”, Control, May 2009 http://www.modelingandcontrol.com/repository/WirelessPrimeTime.pdf

http://www.modelingandcontrol.com/




http://www.isa.org/InTechTemplate.cfm?template=/ContentManagement/ContentDisplay.cfm&ContentID=83041

http://www.isa.org/InTechTemplate.cfm?template=/ContentManagement/ContentDisplay.cfm&ContentID=83041

http://www.controlglobal.com/articles/2010/LevelControl1002.html

http://www.modelingandcontrol.com/repository/WirelessPrimeTime.pdf