Emerson Exchange 365

How do you know when a startup has gone wrong, it is time to retire, your mentor is an endangered species and you mentor’s book will become a college text? These and other questions you have not asked will be answered. Read the full text.

There is not a whole lot of current information on the response time of pH electrodes. Tests done in the 1960s for a clean, healthy pH glass electrode showed that the time constant was smaller for a positive pH change, a higher velocity, and a higher degree of buffering. For a buffered solution at 4 [...] Read the full text.

I have managed hundreds of projects and engineers over my career, and one of the most important concepts I stress to my team is to tell me the complete truth − NOT what I want to hear. If a project is running behind schedule, I need to know NOW so I can adjust and possibly [...] Read the full text.

The power of the PID largely remains underutilized. Most of the options and parameters other than scale ranges and tuning settings remain at their defaults. Here we look how to tap into the incredible capability of the PID to minimize batch cycle time and startup time and to maximize production capacity, flexibility, and efficiency while reducing disruption to utility, raw material, and reagent systems. Also detailed is a simple method to compensate for dead time and to eliminate limit cycles. Read the full text.

If you look at a process flow diagram, you quickly realize that the flows are designed to move up and down in unison. The ratios of the flows are maintained. If you double production rate, you can double the process flows as a first approximation. The utility flows for heating and boilup will probably double [...] Read the full text.

Consider the stereotype of the engineer. He (or she) is shy, socially inept, and rarely the life of the party. Understanding Fourier transforms and partial differential equations is no problem but standing in front of an audience and giving a presentation is a nearly insurmountable challenge. If he does give a talk he tends to [...] Read the full text.

Advanced regulatory control seeks to incorporate knowledge of process dynamics, disturbances, constraints, and objectives to increase process efficiency and capacity. The PID power and flexibility enables an incredible spectrum of creative opportunities to achieve these goals. Here we look at techniques to preemptively deal with upsets and setpoint changes, protect against abnormal conditions, improve process linearity, compensate for dead time, eliminate limit cycles, reduce valve deadband, improve valve resolution and threshold sensitivity, extend valve rangeability, and optimize process operation. We also consider when to move up to model predictive control. Read the full text.

The value of the external-reset feedback feature in PID controllers is becoming increasingly apparent to me. I got a preview of its importance when I found that 1980s vintage DCS required a fix for override control that was addressed in the next generation of DCS by this feature. This wakeup call was followed by the [...] Read the full text.

If you are the optimistic sort who always sees the good in your fellow man and always takes people and companies at their word – skip to Tip #43 and save yourself the angst. However, if you are like most engineers and tend to be a bit more skeptical and jaded, then this tip is [...] Read the full text.

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. Solutions for the common problem of insufficient flow measurement rangeability are given. Also noted is when cascade control is abandoned in small bioreactors. Read the full text.

Signal characterization to linearize valve installed flow characteristic has a bad reputation due to some practical implementation problems. These problems can be addressed today by doing the characterization in the distributed control system (DCS), but the stigma remains. With pneumatic positioners, signal characterization was done by the use of a cam. Standard cams were based [...] Read the full text.

We have all been there. The sales person stands before the crowd demonstrating a control system. He clicks here and lays down a pump, he clicks there and adds a control valve, he opens this window and everything magically links and is fully functional. The system is a flawless masterpiece. Nothing can go wrong … [...] Read the full text.

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 is too slow or has insufficient rangeability? The fixes are quite simple. Read the full text.

There are many opportunities for process optimization by valve position control (VPC). Table 1 summarizes common examples of the use of VPC for increasing process efficiency and capacity. Efficiency is increased by reducing energy and raw material costs for a given production rate. Capacity is increased by increasing feed rates for a given efficiency. Table [...] Read the full text.

I was born in a very small town in southern Mississippi. From the earliest age, I was taught that every adult was a “ma‘am” or a “sir,” that you always held open doors or gave up your seat on the bus, and that everyone deserved to be treated with respect and courtesy. Later in life [...] Read the full text.

How do you know when interaction is going to be a problem? Why would the control loop design need to be changed? Are there hidden loops? What can you do with tuning to mitigate the problem? When do you need to move on to Model Predictive Control? Hopefully, this blog will provide the answers to these questions and more. Read the full text.

The best way to classify process simulators is to look at the original intent of the simulator software when it was first released, who the software developers were, who configures the models, and how the models are used. Simulators originally designed for system acceptance testing (SAT), operator training systems (OTS), and process control improvement (PCI) [...] Read the full text.

Since most unit operations have more than one control loop, interactions can exist where the PID output of one loop affects the PID process variable of another loop and vice versa. Interactions can cause loops to confusingly burst into oscillations. Here is some guidance on how to reduce the consequences and prevent the initiation of interactions. In the process we realize some principles in the design of control strategies for plantwide control. Read the full text.

The reference electrode should provide a fixed reference potential and a path of electrical continuity from the internal reference element via a porous surface or aperture between the reference electrolyte and the process called a liquid junction. Coating of the reference junction can cause slow equilibration. Process ions, such as cyanide, can cause precipitation of [...] Read the full text.

This tip is actually a compilation of Tip #1 “Never Stop Learning” and Greg’s tip on “Seek Principles,” Tip #66. As a young engineer I spent a great deal of time and effort learning how instrumentation worked. Once I had a thorough understanding of that information, I could evaluate competing instrumentation designs and better select [...] Read the full text.

Control operators would say to me, “Can you do something to slow down the pH changes?” For a setpoint on a steep titration curve, the pH would often zip right past the setpoint on its way from one tail of the curve to the other tail. Titration curve plots from the lab for strong acids [...] Read the full text.

Here is an opportunity to learn how to improve pH and temperature control systems and support ISA as well. Registrants for these web seminars receive a free copy of the respective book and free follow-up answers to questions that can be shared with ISA Mentor Program participants. You can share the opportunity with friends and relatives since there is no additional cost for other people who can see your computer screen. Read the full text.

I was extremely fortunate as a young engineer. Early in my career I took a position as an “instrument engineer” working under a gentleman named Henry Hecht (whom we met earlier). Henry had 50+ years of experience in instrumentation and controls and the other team member, Clyde Barre, had 45 years of experience. I was [...] Read the full text.

What can be done besides the typical analysis for control benefits that show a setpoint can be moved closer to a constraint by reducing variability? Here we take a quick look at five things that can be done to extend this analysis to unknown effects and recognize and seek benefits from a more extensive view. In many cases, the improvements require simple improvements in the existing DCS configuration and modes of operation. Read the full text.

Biopharmaceutical batches are often worth more than a million dollars. The product quality of these batches is sensitive to changes of 0.1 pH and the steam sterilization of electrodes reduces the life and accuracy of a sensor that under the best of conditions is the weakest link in a control system. Yet people looking at [...] Read the full text.