Instrumentation and Controls Topics Page

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Recent Articles

How to get control of your control valves

Assessment and performance testing depend on the control and valve technology.

Compressed air efficiency

In this installment of What Works, Gatorade saved energy and cut operating costs with compressor controls.

Gain control of your process

Sheila Kennedy says control systems can increase speed, security and reliability.

Power to the process

Why a standard is needed for work processes related to intelligent device management.

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White Papers: In Depth Research

Distributed I/O and remote I/O solution improves performance and reliability
Author: Jim McConahay, P.E.
Posted: 09/26/2011
In central New York state, recent upgrades at a municipal water plant have provided the means for operators to enhance their process for meeting the water quality needs of customers. As part of the upgrades, the facility modernized its control system utilizing a distributed I/O and remote I/O solution. This technology reduced wiring costs for field instrumentation while improving operational readiness and reliability.

IEC vs. NEMA push buttons
Posted: 08/08/2011
The globalization of industrial manufacturing has resulted in a convergence of electromechanical operator interface device styling and performance standards. That convergence is evident in the design of push button products.

A common misconception holds that any operator manufactured or designed in Europe is, by definition, an IEC push button. Another is that IEC push buttons are manufactured only in IEC countries. Neither belief is true. Conversely, not all NEMA operators are designed, manufactured, or even sold in the United States or Canada.

What is factual is that the traditional target markets for IEC and NEMA rated devices were Europe and North America, respectively. These traditional markets are expanding with the globalization of product manufacturing, product support and product sales.

An industrial operator interface device can be described by four general characteristics: ingress protection, electrical performance, panel opening size and styling.

Guidelines for industrial Ethernet infrastructure implementation: A control engineer's guide
Posted: 08/01/2011
As part of a continuing effort to make their organizations more efficient and flexible, manufacturers are rapidly migrating to industrial Ethernet technology to network their industrial automation and control systems. The use of standard Ethernet technology enables organizations to control costs by moving from costly plant-optimized networks to a proven technology that is simpler to integrate, requires widely available skills, and is more secure and reliable while still meeting real-time traffic requirements.

This white paper provides an overview of Ethernet technology and implementation guidelines to implement in the both control and information networking environment. It discusses the requirements and consideration in implementing a switched Ethernet architecture in industrial networking environments.

A systematic approach to plantwide control
Posted: 06/27/2011
A chemical plant may have thousands of measurements and control loops. By the term plantwide control it is not meant the tuning and behavior of each of these loops, but rather the control philosophy of the overall plant with emphasis on the structural decisions. In practice, the control system is usually divided into several layers, separated by time scale.

My interest in this field of plantwide control dates back to 1983 when I started my PhD work at Caltech. As an application, I worked on distillation column control, which is an excellent example of a plantwide control problem. I was inspired by Greg Shinskey's book on Distillation Control, which came out with a second edition in 1984 (Shinskey, 1984). In particular, I liked his systematic procedure, which involved computing the steady-state relative gain array (RGA) for 12 different control structures ("configurations"); the DV-configuration, LV-configuration, ratio configuration and so on.

However, when I looked in more detail on the procedure, I discovered that its theoretical basis was weak. First, it did not actually include all structures, and it even eliminated the DB-configuration as "impossible," even through it is workable in practice (Luyben, 1989). Second, controllability theory tells that the steady-state RGA by itself is actually not useful, except that one should avoid pairing on negative gains. Third, the procedure focused on dual composition control, while one in practice uses only single end control, for example, because it may be optimal economically to use maximum heating to maximize the recovery of the valuable product.

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