4-20mA CONTROL LOOPS
This paper reviews the operation and advantages of the 4-20mA transmission standard and loop-powered transmitters. The discussion explains sink vs. source wiring, power requirements, voltage drops, proper grounding, transmission distance, signal noise, live zero calibration and more. The download is free, but registration is required. The direct link is at http://tinyurl.com/dxaqrjw.
CONTROL LOOPS AND DYNAMICS
An explanation of each component of a control system, including valves, actuators, sensors and controllers, is presented with an introduction to methods of control and system dynamics, including simple control loops and feedback systems. Topics covered included open control loops, closed-loop control, disturbances, feedback and feed-forward control, single and multi-loop control and loop dynamics. This presentation has many illustrations, is freely downloadabe, and is at http://tinyurl.com/2ecsfct.
PID CONTROL VIDEOS
PID Loop Tuning Explained, Parts 1 and 2, are YouTube videos showing the basics of PID loop tuning. Part 1 covers proportional. Part 2 covers proportional and integral. The site also contains many links to other loop-tuning videos. The direct link is at http://www.youtube.com/watch?v=IcQQRUdBiGw.
The Controls Freak
THE VOICE OF EXPERIENCE
This is the website of experienced engineer John A. Shaw. It contains brief tutorials and lessons about PID loop control and tuning, the PID control algorithm, writing software for the PID algorithm, cascade control, ratio control and more.
TUNING LEVEL CONTROLLERS
F. Greg Shinskey explores the special needs of managing level loops. Level loops differ from others in their economic objectives. There may be no economic penalty associated with a particular deviation from setpoint, but a loss of level control can shut down an entire plant. Their task is to regulate a process that is fundamentally non-self-regulating, leading to limit-cycling of a PI (proportional + integral) controller in the presence of any dead band in the control valve, avoided by using either a valve positioner or a cascade flow loop. Categories of level loops covered, based on vessel type and tuning rules that apply to it are: surge tanks feeding critical processes; material-balance regulators between process stages; levels affected by shrink-swell and inverse response, such as boiler drums; and levels with resonance (manometer effect). The direct link is at http://tinyurl.com/cjdysnv.
PID CONTROL IN 13 PAGES
This 13-page, downloadable PDF covers all the basics of PID control. It introduces the proportional-integral- derivative (PID) control algorithm, discusses the role of the three modes of the algorithm, highlights different algorithm structures, and discusses methods that have evolved over the last 50 years as aids in control loop tuning. The direct link is at www.pacontrol.com/download/Proportional-Integral-Derivative-PID-Controls.pdf.
MPC KNOWLEDGE CLEARINGHOUSE
Multivariable predictive control (MVPC) is the most popular and successful computer control technology in the refining and petrochemical industries. This site has information needed to help users make informed decisions about MVPCs that will benefit APC applications for operating units. The information is provided in various forms from publications and typical examples to actual installations and experiences reported by practitioners in the field. It also has forums, technical chats and questions and answers.
CONTROL TUNING BLOG
Control's long-time columnist, Greg McMillan, is the author of the Control Talk blog found at http://www.controlglobal.com/. Greg covers all manner of tuning questions, tips, suggestions and techniques for handling your most challenging loop-tuning and other control questions. The direct link is at http://community.controlglobal.com/controltalkblog.