control using two manipulated parametersmodelingandcontrol.com/repository/twomanipcontrol.pdf ·...

©2006Fisher-Rosemount Systems, Inc.Slide 1- 1

Control Using Two Manipulated Parameters

Control Using Two Control Using Two Manipulated Parameters Manipulated Parameters


Process Control Introduction – Historic Perspective

IntroductionIntroductionOverview – Typical ExamplesSplit-Range Control

– Concept, variations in implementation– Setup in field vs. Splitter Block and IO for each valve. – Using Splitter Block, Example.

Valve Position Control– Concept and typical implementation– Setup of I-only control in implementation – Impact of mode/status, Example.

Combining Split Range and Valve Position Control– How to implement in DeltaV– Example

Summary



Control Using Two Manipulated ParametersControl Using Two Manipulated ParametersControl Using Two Manipulated ParametersUnder specified problem that has multiple solutions for unlimited operation.

Extra degree of freedom is used to achieve unique solution that satisfied specific control objective.

Most common techniques are: split range, valve position control.

Combination of these techniques offer new capability to address this class of problems

Controller Process

SP

Unmeasured Disturbance

One(1) Controlled Parameter

Two(2) Manipulated Parameters



Split Range – Traditional Implementation Split Range Split Range –– Traditional Implementation Traditional Implementation Sequencing of valve accomplished through calibration of positioner, selection of actuator (A/O or A/C)

Pro – Less expensive installation (1 pair of wires to field and 1 I/P)

Con -Difficult to initially calibrate and continuously improve to get best gap and most constant gain.

Con -Individual valves not accessible for trouble shooting loop and actuator/valve problem.

Con – The actuator, pneumatic positioner, and I/P performance shift with time and field conditions

Con – I/P failure disables 2 valves. Replacements in the night may not have the special settings

IP101

TT101

TIC101

Process

Temperature Example

4-20ma

Heating

Cooling

3-15PSI

ValvePosition(% of Span)

IP Output ( PSI )153

0

100Cooling Heating

A/C

A/O



Split Range – Traditional ImplementationSplit Range Split Range –– Traditional ImplementationTraditional ImplementationSequencing of fine and coarse valve requires pressure switch, two solenoid valves and associated wiring and tubing

Con – Complex installation

Con -Difficult to initially calibrate and continuously improve to get best gap and most constant gain.

Con -Individual valves not accessible for trouble shooting loop and actuator/valve problem.

Con – The switch, actuator, pneumatic positioner, and I/P performance shift with time and field conditions

Con – I/P failure disables 2 valves. Replacements in the night may not have the special settings

IP102

AT102

AIC102

Process

pH Example

4-20ma

Coarse ValveFine Valve

3-15PSI

A/O

pH


I/P Output ( PSI )1530

100Fine ValveCoarse Valve

A/O

PS102



Split Range – DeltaV Implementation Split Range Split Range –– DeltaV Implementation DeltaV Implementation Splitter bock is used to implement split range control.

When using traditional valves, split range control may implemented in DeltaV Controller using two(2) current outputs

Split range control may be partially or fully assigned to fieldbus devices.

AI PID SPLT

AO

AO

AI PID SPLT

AO

AO



Split Range Control in DeltaVSplit Range Control in DeltaVSplit Range Control in DeltaV



Splitter Block CalculationSplitter Block CalculationSplitter Block Calculation



IN_ARRAY ParameterIN_ARRAY ParameterIN_ARRAY ParameterThe SP range associated with each output is defined by IN_ARRAY. SP range of outputs may be defined to overlapThe SP upper end of range must be greater that lower end of range for each output

SP range associated with OUT1

SP range associated with OUT2



OUT_ARRAY ParameterOUT_ARRAY ParameterOUT_ARRAY ParameterWhen SP is outside defined range, then the value at the end of range is used to determine the output.

LOCKVAL determines if OUT1 value is held if SP is greater that the upper end of range defined for OUT1.

No restrictions are placed on the output range.

OUT1 Range for associated SP range



Splitter BlockSplitter BlockSplitter Block

SP

0 1000

100

0

100

0

100

100

100

0

0

OUT_1

OUT_2

LOCK_VAL “holds ”

LOCK_VAL “is zero ”

OUT_ARRAY0 100 0 100

IN_ARRAY0 100 0 100

OUT_ARRAY100 0 0 100IN_ARRAY0 40 35 100

OUT_ARRAY0 100 0 100IN_ARRAY0 40 35 100HYSTVAL



AI PID SPLT

AO

AO

IP103A IP

103B TT103

FY103

TIC103

COOLERHEATER

TT103 TIC103 FY103 IP103A

IP103B

Slaker – Heating/Cooing ExampleSlakerSlaker –– Heating/Cooing ExampleHeating/Cooing Example




TIC103 Output (% of Span)1000

0

100

Cooling (IP103B)

Heating (IP103A)

Split Range Output (FY103)Split Range Output (FY103)Split Range Output (FY103)



AI PID SPLT

AO

AO

IP104A

IP104B

PT104

FY104

PIC104

PT104 PIC104 FY104 IP104A

IP104B

Steam Header ExampleSteam Header ExampleSteam Header Example

400# Header

1475# HeaderBoiler

Turbo Generator




PIC104 Output (% of Span)1000

0

100

Valve 104A

Valve 104B

Split Range Output (FY104) - CapacitySplit Range Output (FY104) Split Range Output (FY104) -- CapacityCapacity



Calculating Splitter SP RangesCalculating Splitter SP RangesCalculating Splitter SP RangesA 1% change in controller output to the splitter should have the same impact on control parameter when operating with either valve.When manipulating the same or similar material e.g. steam flow to header, then the range may be calculated based on valve rating. Tests may be performed to determine impact of each valve on the controlled parameter.

Example: Steam flow to Header, splitter interfacing directly to PRV’s, no overlap

Valve 1 rating = 50kph

Valve2 rating = 150kph

Desired Splitter Span valve 1 = 100*(50/(150+50)) = 25%

SP range for valve 1 = 0-25%

SP range for valve 2 = 25-100%



Testing Process to Determine Splitter SP RangesTesting Process to Determine Testing Process to Determine Splitter SP RangesSplitter SP Ranges

With the process at steady state and AO’s in Auto mode, determine the magnitude of change in the controlled parameter for a 1 percent change in each valve.Calculate the splitter SP span and range for each output based on the observed response

Time

CoolingHeating 1%

1%

1.1degF 2.2degF

Desired Splitter Span cooling valve = 100*(2.2/(1.1+2.2)) = 66%

SP range for cooling valve = 0-66%SP range for heating valve = 66-100%

Controlled Temperature

Example: Slaker feed temperature controlled using heating and cooling valves



Example – Split RangeExample Example –– Split RangeSplit Range



Response to SP Change – Split Range Output To Large Valve/Small ValveResponse to SP Change Response to SP Change –– Split Range Split Range Output To Large Valve/Small ValveOutput To Large Valve/Small Valve

Small Valve

Large Valve

PID OUT

SP

PV



Split Range – Strengths and WeaknessesSplit Range Split Range –– Strengths and WeaknessesStrengths and WeaknessesPro - Process operation in simplified since two actuators are treated as one control manipulated parameter.

Pro – immediate change in target actuator position can be achieved over the entire operating range independent of the size of change in the splitter SP

Con – To achieve stable control over the entire operating range, controller tuning must be established based on the slower responding manipulated parameter.

Con- Does not take advantage of difference in resolution of actuator e.g. fine vs. coarse valve.

Valve position control may be used in place of split range control when there are differences in dynamic response or resolution in actuators.



Valve Position Control – Traditional Implementation Valve Position Control Valve Position Control –– Traditional Traditional Implementation Implementation

IP106A

AT106

AIC106

Process

PID control is implemented using the actuator with finer resolution or fastest impact on controlled parameter

The actuator with coarse resolution or slower impact on the controlled parameter is adjusted by an I-only controller to maintain the long term output of the PID controller at a given target

I-Only controller must be disabled when the PID controller is not in an Automatic mode.

pH Example

Fine Valve

A/O

ZC106

IP106B

Coarse Valve

I-Only Controller

Mode

Target Valve Position

Time

pH

Fine Valve

Coarse Valve

Target Valve Position



Valve Position Control – DeltaV Implementation Valve Position Control Valve Position Control –– DeltaV DeltaV Implementation Implementation

I-Only control is achieved by configuration of the PID Block STRUCTURE, GAIN and RESET parameters.

It is possible to implement valve position control in the DeltaV controller or for this function to be distributed to fieldbus devices.

AI PID AO

AI PID

AO

AO

I-Only AO

I-Only

Traditional field devices

Fieldbus devices



Valve Position Control in DeltaV Valve Position Control in DeltaV Valve Position Control in DeltaV Actuator with fastest impact or highest resolution is used to maintain the controlled parameter at setpoint.

The OUT of the PID used for control is wired to IN on the PID block used for I-Only regulation of slower responding or coarse resolution.

PID configured for I-Only control



Configuring PID for I-Only ControlConfiguring PID for IConfiguring PID for I--Only ControlOnly ControlThe STRUCTURE parameter should be configured for “I action on Error, D action on PV”

The GAIN should be set to 1 to allow normal tuning of RESET (even though proportional action is not implemented.

RESET should be set significantly slower than that the product of the PID gain and reset time used for control e.g. 5X slower



AI PID AO

IP107A

IP107B

FT107

FIC107

FT107 FIC107 IP107A

Precise Flow Using Big/Small ValvePrecise Flow Using Big/Small ValvePrecise Flow Using Big/Small Valve

ZC107

I-Only AOIP107B

ZC107



Example -Boiler BTU DemandExample Example --Boiler BTU DemandBoiler BTU Demand

AI PID AOFT109B FIC109 IP109A

ZC109

I-Only AOIP109B

ZC109

FT109A

IP109B

FIC109

FT109B

IP109A

FY109

Low BTU – Waste Fuel

HI BTU Fuel Boiler

BTU Demand

AIFT109A

SUMFY109



Example –Reformer Air DemandExample Example ––Reformer Air DemandReformer Air Demand

ZC110

AI PID AOFT110 FIC110 IP110

ZC110

I-Only AOSC110

FIC110

FT110

SC110

Air Machine

Secondary Reformer

Total Air Demand

IP110



Example – Valve Position ControlExample Example –– Valve Position ControlValve Position Control



Response to SP Change - Valve Position Control with Large Valve/Small Valve Response to SP Change Response to SP Change -- Valve Position Valve Position Control with Large Valve/Small Valve Control with Large Valve/Small Valve

Target position for fine valve is 30%.

When the fine valve saturates, then response is limited to be reset of the I-Only control

Fine Valve

Coarse Valve

SPPV

Limited



Valve Position Control – Strengths and WeaknessesValve Position Control Valve Position Control –– Strengths and Strengths and WeaknessesWeaknesses

Pro – Immediate control response is based on actuator with finest resolution and/or faster impact on controlled parameter.

Pro – Actuator with coarse resolution or slower impact on controlled parameter is automatically adjusted to maintain the output of the controller output long term at a specified operating point.

Con – The controller output may become limited in response to a large disturbance or setpoint change. For this case, the dynamic response becomes limited by the slower tuning of the I-only controller.

The features of split range control and valve position control may be combined to provide immediate response to large changes in demand while retaining the features of valve position control for normal changes.



Combining the Best Features of Split Range and Valve Position ControlCombining the Best Features of Combining the Best Features of Split Range and Valve Position ControlSplit Range and Valve Position Control

A composite Block can be created that combines the features of split range and valve position control

Support for BKCAL_IN and BKCAL_OUT can be implemented to provide bumpless transfer



Composite AlgorithmComposite AlgorithmComposite Algorithm

Filter

CAS_IN

MODE

SP x +

x

x

T

ScalingRANGE SPAN

NORMAL

OUT_1

OUT_2

BKCAL_OUTBKCAL_IN1

BKCAL_IN2

Balance Calculation

-

-FILTER_TC



Composite ImplementationComposite ImplementationComposite ImplementationParameters that must be configure are: FILTER_TC, SPAN (of SP), RANGE (of OUT1), and NORMAL (desired position )

The FILTER_TC should be configured similar to the reset time of the I-Only Controller that would be used for valve position control.



Demo – Composite Combining Valve Position and Split Range ControlDemo Demo –– Composite Combining Valve Composite Combining Valve Position and Split Range ControlPosition and Split Range Control



Example: Response to SP Change Example: Response to SP Change Example: Response to SP Change For small changes in SP or load disturbance, the response is similar to that provided by valve position control

For large changes in SP or load disturbance, the immediate response is similar to split range control

SP, PV

OUT of PID

Fine Valve

Coarse Valve

Small change Large change



SummarySummarySummarySplit range control allows fully dynamic response to major setpoint of load disturbance changes.

Valve position control may be used to takes advantage of any difference in control response or resolution in the manipulated parameters.

A composite block has been demonstrated that combines the best features of split range and valve position control.

control using two manipulated parametersmodelingandcontrol.com/repository/twomanipcontrol.pdf ·...

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