Cascade control may be applied when a process is composed of two or more (sub)processes in series. To apply cascade control, the output of each of these processes must be measured. The input to the first process is directly manipulated. Since the output of each process in the series is the primary input of the …
Monthly Archive: January 2011
Jan
27
Smart Adaptive Feedforward Control
Feedforward can make disturbances worse unless intelligence corrects the intensity and timing of the feedforward signal for unknowns. It would be nice if the feedforward signal was the whole story. Unfortunately there are many unknowns in terms of disturbances, dynamics, and errors. An unknown disturbance can be driving the process variable in the opposite direction …
Jan
24
Feedforward Control
One of the fundamental limitations of single-loop control is the fact that all control action is based on the error between the setpoint and the controlled parameter. If there is no error, then the control output will remain at its last value. To correct for process disturbance input using single-loop control, the disturbance input must …
Jan
20
We are ISA
We are the past, present, and future of ISA. Our participation and leadership defines ISA and in so doing our profession. We have been fortunate to have key members step up to be leaders at the local section, division, and national level. We have had an extraordinary past leader (Vernon Trevathan) and new leader (Nick …
Jan
17
Tuning and Loop Performance
During the commissioning of feedback control based on the PID algorithm, the tuning parameters associated with the PID (that is, the proportional, integral and derivative gain) must be set to specific values to achieve the best controller response to setpoint and disturbance input changes. The PID tuning parameters are normally specified as positive, floating-point values …
Jan
11
Universal Concept – Bias
The simplest correction to models and measurements turns out to be the most widely applicable correction. Whether you are correcting a model for feedforward control, model predictive control, or a neural network prediction or correcting a measurement of composition, flow, level pressure, pH, or temperature the simple bias rules. I am a biased when it …
Jan
10
PID Feedback Control
Many processes have measured and unmeasured disturbance inputs that can significantly impact the value of the controlled and constraint outputs. Process plants are often quite complex and it is not possible for the operating staff to safely and efficiently control the process manually during normal operation. The most common means of providing automatic feedback control …
Jan
06
Review of Deminar #11 – Feedforward Control -Timing is Everything
You can have the best feedforward measurement and accurate feedforward gain and still do more harm than good with feedforward control. If the feedforward correction does not arrive at the same time at the same place in the process as the disturbance, an irregular, oscillatory, and confusing response can occur. If the feedforward signal arrives …
Jan
05
Feedforward Control using PID and PIDPlus – Deminar 11 Starts in 15 minutes
Update: You can join today’s Deminar at http://bit.ly/JC-LiveMeeting. Deminar 11 “How to Setup and Adjust the Dynamic Compensation of Feedforward Signals” has been rescheduled from Wed Dec 1 to Wed Jan 5 (10 am CST). We will explore the adjustment of feedforward delay, lead-lag, and gain for the traditional PID and the smart PID for …
Jan
03
Process Characterization – Integrating Process
In some cases, a step change in a process input will result in the process output changing continuously. A process that exhibits such a response is known as an integrating process. As part of the chapter on process characterization in Chapter 9 of Control Loop Foundation, we address integrating process response. In the process industry, …
