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Introduction to Process ControlFG05W1 Version 1.3© 2010

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Seminar Logistics

• Seminar materials– Downloadable presentation– Question and Answer session (audio and email)– Survey– Earn 1.5 Professional Development Hours (PDH)

• Seminar length– 90 minute total presentation – Three approximately 20 minute instructional presentations– Three approximately 10-minute question and answer sessions

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Audio Instructions

• Please note the following during the seminar:• As a participant, you are in a “listen-only” mode.• You may ask questions via the internet, using your

keyboard, at any time during the presentation. • However, the presenter may decide to wait to answer

your question until the next Q&A Session.

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Audio Instructions for Q & A Sessions

• Questions may be asked via your telephone line. • Press the *1 key on your telephone key-pad. • If there are no other callers on the line, the operator will

announce your name and affiliation to the audience and then ask for your question.

• If other participants are asking questions, you will be placed into a queue until you are first in line.

• While in the queue, you will be in a listen-only mode until the operator indicates that your phone has been activated. The operator will announce your name and affiliation and then ask for your question.

Introduction of Presenter

• Instructor– Name: William (Tim) Shaw – PhD, CISSP– Background/experience: Over 30 years of

experience with computer based automation systems including developing three generations of DCS systems and two generations of SCADA systems. Former Adjunct Professor in the Graduate Engineering department of Loyola College in Baltimore. Authored books on Batch Process Control and on SCADA Cyber Security. Currently the Senior Consultant for Cyber SECurity Consulting, an industrial automation cyber security firm. Tim periodically teaches courses for ISA and IEEE.

Email: timshaw4@verizon.net

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Goals of this training session

• Discuss the operation and components of a feedback control loop

• Explain the role of measurement and control in industrial processes

• Interpret measurement and control technology• Discuss the fundamental concepts of controller tuning

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Section 1: Basics of Process Control

• Process/Process Control Defined• Process Control Loop• Measurement Loop• Control Loop• Setpoint• Steps

– Measure– Compare– Decide– Action

• P&ID drawings

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Definition of a Process

A process is a part of a manufacturing plant in which material or energy is converted to other forms of material or energy

– Change in pressure, temperature, speed, electrical potential, etc.

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Basic Feedback Loop

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Process Control Loop

Process Control: the regulation or manipulation of variables influencing

the conduct of a process in such a way as to obtain a product of desired

quality and quantity in an efficient manner

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Control Steps

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Process Pictorial

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Another Pictorial View

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Control Loop on a P & I D

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Steps Again

• Measure– Quantify – Standardize

• Compare – To Desired Value (Setpoint)

• Decide– How much – How long– How quickly

• Action– Manipulate Variable

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Feedback

• Because you take information about a process output and use it to control a process input (feedback)

• Process must be upset before deviation can be measured

• Always a lag in action due to steps

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Review of Key Items

• Process/Process Control Defined• Process Control Loop• Measurement Side• Control Side• Setpoint• Steps

– Measure– Compare– Decide– Action

• P&ID drawings

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Question and Answer Session

• During Q&A, questions may be asked via your telephone line. • Press the *1 key on your telephone key-pad. • If there are no other callers on the line, the operator will

announce your name and affiliation to the audience and then ask for your question.

• If other participants are asking questions, you will be placed into a queue until you are first in line.

• While in the queue, you will be in a listen-only mode until the operator indicates that your phone has been activated. The operator will announce your name and affiliation and then ask for your question.

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Section 2: The Measurement Loop

• Process Variables• Instrument Zero• Instrument Full Scale• Standard Signals• Engineering vs. Percent • Accuracy• Repeatability• Other Measurement Terminologies• Ranging and Calibration

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Process Variables

• The following variables (one or more) will be found in the majority of process control applications:– Flow– Level– Pressure– Temperature

• There are many others, yet those above are found most often.

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Flow Measurement

Volumetric Mass

Velocity Inferential

Positive Displacement Coriolis MassThermal

Differential PressureTargetVariable Area

MagneticOscillatoryTurbineUltrasonic

(gallons per minute, cubic feet per minute,liters per minute, etc.)

(pounds per hour, kilograms per hour,etc.)

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Pressure

Pressure Is Force Per Unit Area

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Level Measurement

How far from fullHow far from emptyHow much material

WHERE

HOWMUCH

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Temperature Measurement

How much heat energy?

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Standard Signal Concept

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Standard Signal for Flow

Repeatability vs. Accuracy

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Zero & Span Errors

100%TRUE VALUE0

100%

MEASUREDVALUE

ERROR CAUSED BY INCORRECT ZERO

MEASUREDVALUE

100%TRUE0

100%

ERRORCAUSEDBY SPAN

IDEAL SPAN

HIGH SPAN

LOW SPAN

VALUE

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Non-linearity Error

100%TRUE VALUE0

100%

MEASUREDVALUE ERROR CAUSED

BY NONLINEARITY

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Other Terminologies

• Resolution

– Smallest scale increments

• Sensitivity

– Smallest detectable change

• Hysteresis

– Difference in measurement output when measuring input ascending and descending

• Dead band– Range in which input signal may change upon reversal of

direction without causing measurable change in output

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Ranging (or Scaling) vs. Calibration

• Ranging changes the Instrument zero and/or Instrument Span • Range is always given as “from “, “to “

– Instrument zero is set to lower range value– Instrument span is set so 100% = upper range value

• Modern Instruments do not have to be calibrated upon a range change.

• Calibration means to compare this instrument’s readings for a selected set to a measurement standard in a standardized environment. And adjust if necessary

• Some of the more modern test instruments are shop standards

• Smart Instruments have their own built in standards, or at leastcharacterization curves for sensor linearization.

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Review of Key Points

• Process Variables• Instrument Zero• Instrument Full Scale• Standard Signals• Engineering vs. Percent • Accuracy• Repeatability• Other Measurement Terminologies• Ranging (Scaling) and Calibration

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Question and Answer Session

• During Q&A, questions may be asked via your telephone line. • Press the *1 key on your telephone key-pad. • If there are no other callers on the line, the operator will

announce your name and affiliation to the audience and then ask for your question.

• If other participants are asking questions, you will be placed into a queue until you are first in line.

• While in the queue, you will be in a listen-only mode until the operator indicates that your phone has been activated. The operator will announce your name and affiliation and then ask for your question.

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Section 3: Control Loop/Controllers

• Two Wire Loops• Output Signals• Transducers• Valves• Actuators• Controller Action• On-Off• Proportional Only• Proportional-Integral• Proportional-Integral-Derivative• Tuning

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Two Wire Loop

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Transducers

• Many Final Control Elements in continuous control are valves, and valves use a pneumatic actuator. Most controllers are electronic and have an electronic output. A transducer (I/P) is used to provide an interface.

Current to Pneumatic (I/P) Transducer

• Used to convert current signal to pressure signal

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Control Valves

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Typical Pneumatic Actuator

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Typical Pneumatic Valve Positioner

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Controller Action

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On-Off Control

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Proportional Control Algorithm

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PI Algorithm

dteT

eKmi

c ��

���

�+= �

1

Gain adjustment Integral Time Adjustment

(minutes per repeat)

average error over time

Integral action is used to eliminate the offset that occurs in aproportional controlled process when a load change or continuing error to one side of set point occurs. Operates on duration of error

Integral action also known as reset

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PID Algorithm

� � ��

��� ��

���

�

�

�= + +�

��

�

���

�

gain adjustment

integral time adjustment

derivative time adjustment (minutes)

Rate of error change over time

Derivative is used on slow processes to reduce over/undershoot, providing less excursion from setpoint and a quicker first return to setpoint. Operates of the rate of error change.

Derivative action also known as rate

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Tuning Objectives

• Adjustment of gain, reset, and rate to achieve “good” process control

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Action Summary

ACTION OPERATES ON

On-Off Presence of error

Proportional Magnitude of error

Integral Duration of error

Derivative Rate of Change of error

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Review of Key Steps

• Two Wire Loops• Output Signals• Transducers• Actuators• Valves• Controller Action• On-Off• Proportional Only• Proportional-Integral• Proportional-Integral-Derivative• Tuning

How Many People Are at Your Site?

• Poll Slide• Click on the appropriate number indicating the number of

people that are at your site.

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Question & Answer Session

• During Q&A, questions may be asked via your telephone line. • Press the *1 key on your telephone key-pad. • If there are no other callers on the line, the operator will

announce your name and affiliation to the audience and then ask for your question.

• If other participants are asking questions, you will be placed into a queue until you are first in line.

• While in the queue, you will be in a listen-only mode until the operator indicates that your phone has been activated. The operator will announce your name and affiliation and then ask for your question.

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Related ISA Courses

• FG07 Introduction to Industrial Automation and Control• TC05 Tuning Control Loops• TS00 CCST Review Course

• All ISA courses are available any time as on-site training • For more information: www.isa.org/training

or (919) 549-8411

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ISA Certifications

• Certified Automation Professionals ® (CAP ®)– www.isa.org/CAP

• Certified Control Systems Technician® (CCST®)– www.isa.org/CCST

• Please visit us online for more information on any of these programs, or call (919) 549-8411.

Please take our Web Seminar Surveyvia Zoomerang

The seminar survey was sent to you via email during the seminar. Please do not forget to complete the Zoomerang survey.

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Conclusion

This is the end of:

Introduction to Process Control