Topic

 

Process Control Concepts and Practice

The chemical process industries (CPI) convert natural resources into useful products.  The CPI sectors include pulp & paper, glass, petroleum refining, mineral refining, chemicals, polymers, food, paint, pharmaceuticals, water purification, fragrances, etc. 

Process control differs from many other application domains (such as mechatronics, aerospace, electronic, manufacturing, and distribution), because chemical processes are typically nonlinear, interactive, noisy, have delays, have constraints (associated with safety, loss prevention, and product specifications), and are managed by low cost (low computing power) devices and, typically, by folks at an associate degree level.  Fortunately, the slow dynamics of most processes, another differentiating characteristic, make control manageable.

A journey through the essential and fundamental concepts of automatic control of continuous process, which includes the in-batch control of batch processes, is aimed to provide:

  1. Practice-oriented context and conceptual support for a chemical engineering first course in process control, and
  2. Information for a practitioner needing to independently learn the essentials. 

Texts for college courses typically do an excellent job in deriving equations and exercising mathematical analysis.  But also, typically, texts that support the professor’s preferences of the content for upper-level Chemical Engineering courses, emphasize theory and mathematical analysis, necessarily in an idealized context.  The resources here provide the practicable complementary context and practices, and a hope is that instructors and textbook authors will use the material in this journey to complement their other learning resources.

Excellent sources of such supporting material can be found on web sites:

https://r3eda.com – Russ Rhinehart’s posting on materials and VBA simulators related to control, optimization, regression, steady state detection, and professional development.

https://controlguru.com – Doug Cooper‘s postings on materials and simulators for process control. Now managed by Dennis Nash, president of ControlStation.

https://www.opticontrols.com/ - Jacques Smuts’ postings on materials, book, and simulators for process control.

To come - various postings by Greg McMillan

https://www.aiche.org/community/sites/divisions-forums/computing-systems-technology-division-cast - AIChE’s Computer and Systems Technology Division which posts various newsletter articles and white papers.

https://github.com/A-make/awesome-control-theory - a diverse posting of materials and simulators.

This topic includes the following resources and journeys:

 

 

No! Not Laplace Transforms

R. Russell Rhinehart
60 min
Intermediate
Course
Theory

In my 13-year industrial career, I never used Laplace transforms.  However, transfer functions and block diagram notation are efficient methods to describe dynamic behaviors, and are often...

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FOPDT Models from Skyline Inputs

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

The classic textbook method to generate FOPDT models is the reaction curve technique, a pre-computer era technique:  Start from a steady state, make a step and hold in the controller output...

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Understanding P, I, and D

R. Russell Rhinehart
30 min
Intermediate
Article / Blog
Theory

Understanding what the proportional, integral, and derivative terms do within the PID controller is essential to choose appropriate action, trouble shoot controllers, chose appropriate...

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Min IAE Tuning

Jacques Smuts
15 min
Intermediate
Article / Blog
Application

Procedure and Commentary on tuning for minimum Integral of the Absolute Error

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Understanding Valve Flow Characteristics

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

The response of flow rate through a control valve depends on the friction losses in the piping in which it is installed as well as the controller signal.  The installed characteristic (a...

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PID Explained

Jacques Smuts
20 min
Beginner
Article / Blog
Theory

A qualitative explanation of P, I, & D actions using graphs.

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PID Controller Variations

R. Russell Rhinehart
20 min
Intermediate
Article / Blog
Application

It is important to understand the variations on the PID algorithm when tuning and when choosing a version that is consistent within your use context.  Unfortunately, there are many names for...

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Bumpless Transfer and Tuning

Jacques Smuts
15 min
Intermediate
Article / Blog
Application

Switching from MAN to AUTO mode or LOCAL to CASCADE or changing the controller integral time should not cause a change in the controller output, a bump.  But a primitive coding of the PID...

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Cohen-Coon Tuning

Jacques Smuts
15 min
Intermediate
Article / Blog
Application

A procedure and commentary on this tuning approach that includes deadtime.

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Process Control is Inventory Control

R. Russell Rhinehart
10 min
Beginner
Article / Blog
Application

You change the inventory of heat to change temperature.  You change the inventory of material to change level.  Understanding how the inventory relates to the controlled variable is...

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Control Valve Problems

Jacques Smuts
20 min
Intermediate
Article / Blog
Application

Control valve problems can severely affect control loop performance and, unless eliminated, they can make controller tuning a challenging (sometimes impossible) task. Some problems are quite...

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Nonlinear Control Output Signal Characterization

R. Russell Rhinehart
15 min
Intermediate
Article / Blog
Application

If the process gain makes large changes over the operating range, then tuning PID (or other linear) controllers is difficult.  If tuned for one region, the controller is undesirably sluggish...

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Measurements, Transmission Signals, and Issues

R. Russell Rhinehart
45 min
Intermediate
Article / Blog
Application

This is an introduction to scaled information transmission signals (for example 4-20 mA, 3-15 psig, etc.), the actual sensed signals (like using orifice dP to infer flow rate, or temperature...

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