The automation profession suffers from the lack of a common understanding of the terms used and their units. By taking a closer look at key terms for plant dynamics, we can have more intelligent discussions and better recognition of the contributing factors so that we can find what part of...
Batch process control can seem like another world compared to continuous process control. In batch operations, process conditions are constantly changing and control loops are going in and out of service. PID control may take a back seat to sequential scheduling of manipulated flows.
All feedforward control systems can be reduced to a common form that enables a better understanding and recognition that leads to the best performance and the best interface for the operator. For “smart controls” to be fully appreciated and utilized, the operator needs to know what is going on and...
Often arguments as to whether a linear or equal percentage trim is best are based on the theoretical inherent flow characteristics. Valve rangeability is often stated as simply a deviation of the catalog flow characteristic from the theoretical characteristic.
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.
The power of the PID largely remains untapped. I have recently documented the extensive capability of the PID but being a realist, I expect MPC is going to take over more and more of the role of the PID.
The amount of information that the generalist needs to know is staggering. The knowledge needed is buried in a hundred thousand pages of publications and presentations that are oriented toward the specialist. Here I provide the essentials for the best field instrumentation system.
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.
Each process test will typically give a different result in the process dynamics identified and consequential tuning settings calculated. Here we look at the sources of this lack of repeatability, the implications, and what can be done to improve tuning tests.
There are some simple diagnostic checks and rules of thumb on tuning adjustments that can be used to find out if there is a problem with the PID tuning and what is the solution. This guidance in conjunction with good tuning software can reduce process variability introduced or aggravated by...