Here we use the broader definition of linearity to mean constant dynamics. A linear control loop has a constant total loop dead time, constant primary and secondary time constants, and a constant open loop gain. This perspective reviews the sources of dynamics and causes of nonlinearity.
Michel Ruel, a frequent source on process control improvement in both my Control Talk Blogs and Columns, offers his concise list of the more memorable mistakes made with actuators, compressed air systems, transmitters, and variable-speed drives.
I have dug deep into my memory to add 21 more items to the list of process, mechanical, and piping design mistakes that have made our job as automation engineers more challenging and in some cases impossible. We learn the most by our mistakes.
The control valve and variable speed drive are the final control elements that directly affect the process by manipulating a flow. The expectation is that these elements do their job and do not adversely affect the tuning and performance of the loop.
We start this series with the steps for the selection and installation of the field measurements and control valves or variable speed drives to enable the control system to meet plant objectives. The measurement is the essential window into the process and manipulating a flow is the essential way to...
Variable speed pumps can save energy when the flow is reduced. However, the turndown of the pump speed may not achievable if there is overheating at low flows, excessive sensitivity at low rpm, and cycling at high destination pressures.