Control Engineering's Process Control Newsletter for May 2000

06/04/2002


In this issue:


Initial PID tuning constant settings (no guarantees)

Control Engineering readers consistently indicate loop analysis and PID tuning articles are among the most useful articles we provide. But establishing valid PID tuning parameters requires determining process dynamics, and that's seldom possible until the process is up and operating. However, that doesn't mean loops must remain in manual until process dynamic testing is completed. Here's a set of very conservative PID settings that can be initially used, but will normally result in sluggish response...but they come with no guarantees.

Gain is in proportional gain (Delta percent output / Delta percent input)
Integral is in repeats per minute
Derivative is in minutes

Loop Type:

Flow

Gain = 3

Integral = 30

Derivative = 0

Temperature

Gain = 1.25

Integral = 0.2

Derivative = 0.05

Level

Gain = 2

Integral = min.

Derivative = 0

Gas pressure

Gain = 10

Integral = min.

Derivative = 0

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U.S. OSHA recognizes ANSI/ISA S84.01

The ANSI/ISA S84.01 standard titled 'Application of Safety Instrumented Systems for Process Industries' was officially recognized as an industry consensus standard for complying with OSHA Process Safety Management (PSM) 1910.119 in late March. Visit www.isa.org/sc/news_articles/1,1513,90,00.html for details.

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Safety system training

Since adding safety system information to our web site in January, content and questions have continually increased. One question that keeps popping up, 'Where can I receive more training on Safety Instrumented Systems?' Most safety system vendors offer a variety of training courses. Four independent sources are:

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Fitting the instrument into the process

Once input, output range, and accuracy have been specified and documented, instrument mounting can begin. Right? Not so fast! Obtaining the paid-for accuracy and performance of modern instrumentation requires adhering to good engineering practices and following manufacturer's installation guidelines. If you missed this important article the first time, now's your chance to ensure what you paid for is what your getting. www.controleng.com/archives/1999/ctl0401.99/04g402.htm .

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OPC advancing and expanding

OPC's (OLE for Process Control) roots are tightly entwined with Microsoft , so when Microsoft introduced BizTalk and jumped on the XML (eXtensible Markup Language) bandwagon, naturally the OPC Foundation jumped on-board as well.

Currently two OPC working groups are underway. One group is focused on developing and promoting flexible, consistent rules and formats for exposing plant floor data using OPC XML. The second group is addressing ways to expand OPC data types to include complex data from a broad array of plant floor devices including: DCSs, PLCs, CNCs, robots, fieldbuses, continuous gauging systems, frequency and vibration monitoring systems, and image acquisition systems. (Dave's thought: OPC may have to change its name to OPF (OLE for Plant Floor) to reflect its wider connectivity capabilities.) Visit www.opc.org for more details.

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May's Control Engineering

Cover: Ethernet I/O Strategies
Several types of fieldbus are battling for market and mind share among control engineers. Meanwhile, several companies are using the ubiquitous, and relatively inexpensive, Ethernet for communicating with I/O devices as well as for information. How does Ethernet hold up for I/O communications? Will it become the de facto standard?

Batch Automation and Control Application
Find out how Genentech Inc.-a large biotechnology company specializing in growth hormones, blood clot dissolvers, cystic fibrosis management, and breast cancer drugs-organized and managed a batch automation and control project. Ever-changing process requirements, 6,000 I/O points, and FDA validation requirements make this more difficult than other projects of similar size.

Sizing Software
Control system providers have made all manner of software available to the control engineer via the Internet. Much of this software was developed to assist users in sizing control hardware and final control elements. Contributing Editor Tracy Coates examines this kind of software and web offerings.

Product Focus: Discrete Sensors
Original Control Engineering research examines discrete sensor trends and user issues. Recent product descriptions from leading suppliers will be included, along with research results.

Back to Basics: Closed-Loop Stability
Understanding how to achieve closed-loop stability requires knowing the basics. Here's a primer on related principles.

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Dave's public service announcement

Got a complaint with something you purchased on the Internet? Visit www.WebAssured.com to file a complaint (and maybe get restitution). WebAssured.com claims to be the only Internet consumer-protection seal of approval provider, listing companies who do well and those who violate WebAssured's Internet standard of ethics.

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Editorial input request

My October article is about the benefits of simulation. I'm collecting short stories from users who are willing to quantify the benefits gained from using simulation. If you have a simulation benefits story to share (about 250 words maximum), send it to me at dharrold@cahners.com .

Also, here's your chance to influence Control Engineering's 2001 editorial calendar. In June, the editors of Control Engineering will meet to plan the editorial calendar for 2001. Send your thoughts on the types and contents of articles that are most useful to you to dharrold@cahners.com .





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