HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
REGISTER   |   LOGIN   |   HELP
William K.
User Rank
Platinum
software tool rejects process disturbances.
William K.   8/10/2011 10:10:25 AM
NO RATINGS
It does not take much skill or effort to produce an unstable process control system, the hard part is producing an optimized one that has very little room for improvement. That is a fact. Optimizing a system is seldom a trivial effort. But I don't think that rejecting disturbances is a good approach, at least not for those systems that are designed to hold something constant in spite of disturbances. In fact, most of the process control systems that I have designed were intended to remove the effect of disturbances.

Of course, in many systems there is more than the control algorithm that influences the system stability, which is why anybody attempting to make the system stable needs to understand the whole system, not just the controller. System time constants that produce delays produce an effective phase-shift, which will usually tend to cause oscillation, or just overshoot. System elasticity will also cause instability, and it must either be compensated for or eliminated. Another characteristic is nonlinearity, where the same amount of correction has a different response , depending on some external condition.

Then there is non-process noise that randomly enters the system, and has very little to do with the process being controlled. Typiaclly that sort of noise needs to be kept out of the system, or at least compensated for, typically by filtering. IT seems like this may be what the software tool takes care of. Unfortunately it is often very difficult to reject the noise once it enters the system, leaving noise rejection through adequate shielding as the far superior choice. The term "shielding" here refers to all kinds of noise shielding, not only to electrical shielding.

Beth Stackpole
User Rank
Blogger
Re: PID RIP
Beth Stackpole   8/9/2011 8:58:06 AM
NO RATINGS
Given the huge advances in software development and the key role software plays today even in mainstream appliances, it's surprising to me that it's taken this long to develop a tool to monitor control system operations and act as an early warning system. Seems like a no-brainer to me. Any sense why this isn't more prevelant, or perhaps, it is?

Douglas Smock
User Rank
Platinum
PID RIP
Douglas Smock   8/9/2011 8:10:32 AM
NO RATINGS
PIDs certainly have done yeoman's duty for the past 100 years, and can certainly be improved where people want to make the effort and investment. Melt flow indexes for material used in a hose extrusion line can vary dramatically, requiring many steps to enhance productivity and product quality. Certainly an improved control algorithm is a good step. In the example cited, the PID is apparently driving heater band performance. Other areas for improvement could be the heating mechanism for the barrel as well as the screw design.



Partner Zone
Latest Analysis
The National Highway Traffic Safety Administrationís recent backup camera mandate could open the door to more vehicle innovations, including better graphical displays, 360-degree camera views, and the increased use of Ethernet.
With support from National Instruments, a group of dedicated students from Connally High School in Austin, where more than 50% of the students are at risk of not graduating, have created a successful robotics team that is competing in the FIRST World Championships.
Solar Impulse 2 -- a 100% solar-powered airplane -- has been completed. It features several advanced materials, some developed specifically for next year's attempted around-the-world flight.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Lumus and eyeSight have partnered to create consumer-grade devices that offer all the prime functions of smart glasses without the bulk.
More:Blogs|News
Design News Webinar Series
3/27/2014 11:00 a.m. California / 2:00 p.m. New York / 7:00 p.m. London
2/27/2014 11:00 a.m. California / 2:00 p.m. New York / 7:00 p.m. London
12/18/2013 Available On Demand
11/20/2013 Available On Demand
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Apr 21 - 25, Creating & Testing Your First RTOS Application Using MQX
SEMESTERS: 1  |  2  |  3  |  4  |  5


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Class: April 29 - Day 1
Sponsored by maxon precision motors
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service