Category: Cascade Control Cascade Rule Interaction Resonance Disturbances PID Controllers PID Tuning Tips
Submitted by Greg McMillan on Wed, 04/15/2015 - 21:25
Most of the control literature focuses on minimizing the integrated absolute error (IAE) for a step disturbance, often in a linear system. In the process industry, there are many other objectives and complications that require special attention.
Submitted by Greg McMillan on Mon, 02/09/2015 - 20:58
A lot of time and money can be spent deciding which valves need positioners and which flows need measurement. We tend to look at short term costs such as hardware and not the cost of troubleshooting and the implications as to plant performance.
Category: Cascade Control Cascade Rule Lambda PID Tuning Rangeability Tips Ultimate Period Valve Positioners
Submitted by Greg McMillan on Fri, 03/21/2014 - 11:09
Given that cascade control loops are everywhere without much consideration as to dynamic requirements, what can we do to make the implementation effective? Here are some specifics by the way of detailed recommendations on the sequence, speed, and setup for tuning PID and digital valve controllers.
Category: PID Tuning Cascade Control Ultimate Period Tips Cascade Rule Lambda Valve Positioners Rangeability
Submitted by Greg McMillan on Sat, 03/08/2014 - 20:16
Did you know all loops today use cascade control? Do you understand how cascade control can correct for lower loop disturbances before they affect the upper loop and can make the upper loop faster? Do you know what to do to keep the system from oscillating if the lower loop...
Submitted by Greg McMillan on Fri, 05/03/2013 - 15:43
A unified approach to tuning has been found that enables a common and simplified method for setting PID tuning parameters. Key features can be used to eliminate the need for retuning to deal with different dynamics and objectives.
Category: Tips Temperature Control pH Control Cascade Control Flow Feedforward Composition Control Control Strategy Interaction Flow Measurement Pressure Control Level Control
Submitted by Greg McMillan on Fri, 04/05/2013 - 01:56
We continue this series with the steps for designing control strategies. Simple rules of thumb will be offered for setting up cascade, composition, flow, level, pH, pressure, and temperature control systems. Examples of common unit operations will help provide understanding of the steps involved.
Submitted by Greg McMillan on Fri, 08/24/2012 - 15:38
Cascade control is an effective way of providing better feedback and feedforward control. The peak error in the primary loop can be reduced by more than an order of magnitude for disturbances originating in the secondary loop.
Category: Surge Control Blending Cascade Control Deadtime Compensator Decoupling External-reset Feedforward Override Control Valve
Submitted by Greg McMillan on Thu, 04/26/2012 - 16:45
The value of a key PID feature is increasingly becoming apparent. I got a preview of the importance when I found the 1980s vintage DCS required a fix for override control that was inherently addressed in the next generation of DCS by this feature.