Educational Resource for Tuning and Control Loop Performance

Process Automation Hall of Fame member, Greg McMillan

Greg McMillan
ISA Fellow

Process automation hall of fame member Greg McMillan has nearly completed an updated version of the book, Tuning and Control Loop Performance: A Practitioner’s Guide. It had last been updated back in 1994. You may be familiar with Greg through his blog posts on the Control Talk and ISA Interchange blogs.

He shared with me that this 4th edition is nearly a 1000 pages long and is a complete rewrite of the 1994 3rd edition. Greg noted that a lot has happened and he has learned a lot in the last 20 years. The book shows how lambda tuning and external reset feedback (e.g. DeltaV Dynamic Reset Limit) can be used to overcome challenges associated with lag-dominance, cascade control, slow valves, interactions, nonlinearities, resonance, and valve position control.

This book will be available this fall and I will update the post when it is available for ordering. If you are interested in knowing when it will be available follow Greg in Twitter and/or connect with him in LinkedIn and he’ll share the news with you.

Here is the current draft of the preface from the book to better understand the scope of the changes: Continue Reading

How Reproducible is Your Repeatable Measurement System?

When it comes to flowmetering systems in your facility, what is the best way to measure its true performance?

Karl Stappert Flow Solutions Advisor

Karl Stappert
Flow Solutions Advisor

R & R: How reproducible is your highly repeatable metering system?In a Flow Control magazine article, R & R: How reproducible is your highly repeatable metering system?, Emerson’s Karl Stappert, of the Flow Solutions team, addresses these important concepts—repeatability and reproducibility.

Karl opens defining the two terms. Repeatability is the sensor’s ability to provide the same flow indication [repeatedly] at unchanging process conditions. These conditions include flow rate, fluid properties, temperature, and pressure to name a few. He defines condition of repeatability: a condition, out of

…a set of conditions, that includes the same measurement, same operating conditions (process and ambient), same location, and replicate measurements on the same object over a short timeframe.

Measurement device product specifications:

…often called accuracy, is achieved under specific conditions of repeatability.

The issue is, of course, that operating plants rarely have these conditions of repeatability. Unlike a calibration laboratory, they are constantly changing. Karl notes that repeatability is one of the most discussed statistical quality measures used for measurement instruments and that turbine meters are one of the most repeatable flow measurement technologies available. Continue Reading

LACT Unit Base Volume versus Base Prover Volume

Update: I should have also mentioned that Rossella will be conducting an October 15 webinar, Optimizing Wellpad Custody Transfer of Liquid Hydrocarbons. If you’re in the onshore oil & gas industry, you’ll want to register and bring your custody transfer questions.

The custody transfer process exchanging oil & gas production between business entities is a critical part of the overall production process. I received this question to an earlier post, How to Prove Your LACT Meter:

I was wondering if you could explain the difference between Base Volume and Base Prover Volume when proving meters.

In that post, Emerson’s Rossella Mimmi shared how provers were used to compare a known volume against the Lease Automatic Custody Transfer (LACT) unit’s flow meter output, where the ratio between the prover reference volume and the meter reading is the meter factor, which is used to correct the meter reading.

I shared this question with Rossella and asked her if she could help me explain the difference. She explained:

Rossella Mimmi  Pipeline Oil & Gas Industry Manager Flow Solutions Group

Rossella Mimmi
Pipeline Oil & Gas Industry Manager
Flow Solutions Group

I think the question refers to how the meter factor is calculated, dividing the prover reference volume by the base volume. Basically two quantities are compared, one is the volume actually measured by the flow meter, the other one is a reference known volume that is the prover’s one.

This is a prover’s operating principle:

Daniel-48in-Pipe-ProverThe prover consists of a length of pipe whose internal volume has been very accurately determined; the displacer is forced to travel at the same velocity as the liquid in the pipe. During meter calibration the meter and the prover are connected in series so that the volume swept out by the piston or sphere can be compared with the volume registered by the meter whilst liquid is flowing steadily from one to the other. As the displacer enters the calibrated pipe section it trips a detector, thereby initiating a count of pulses from the meter under calibration. Continue Reading

Enhancing Industrial Process Reliability using Nanotechnology

Robert Ferris, Ph.D. Strategic Planner

Robert Ferris, Ph.D.
Strategic Planner

Author: Robert Ferris, Ph.D.

Nanotechnology-enabled products are offering real value in equipment reliability

Reliability is the hot-topic in the automation world right now. Nearly every major company, ranging from BHP Billiton, BP, or BASF, has identified process reliability as essential for long-term productivity and profitability. Everybody wins when you improve plant reliability; there is increased production, safety, and lower operating costs. This means more revenue, more margin, and happier workers. Isn’t that nice.

Figure 1. Reliability is both a production a safety concern. (photo1 link, photo 2 link)

Figure 1. Reliability is both a production a safety concern. (photo1 link, photo 2 link)

Reliability, however, is a hard fought battle to gain sustainable improvements. Usually a step change in reliability requires a systematic change in how the plant operates, including; cross-disciplinary initiatives, operation practices, maintenance scheduling, inventory management, documentation, and even equipment suppliers. Continue Reading

How Good is Your Level Control?

So asks Emerson’s Lou Heavner in a thought-provoking post in the DeltaV track of the Emerson Exchange 365 community.

Lou opens:

Lou Heavner Systems/Project Engineering Consultant

Lou Heavner
Systems/Project Engineering Consultant

Is it good enough? Is it too good? Do you even know? Should you care?

Well yes, you probably should care. Most level processes are non-self-regulating or integrating processes. Everything you probably learned about tuning PID self-regulating loops like flow, pressure, and temperature does not work quite the same on integrating processes. So it is quite common for level loops to be tuned “by the seat of the pants” or trial and error. Furthermore, most level loops are tuned to achieve good setpoint response and yet most level loops have one setpoint (typically 50% of the tank height) and rarely is the setpoint ever changed. It is usually more important to consider the response to load disturbances. Even if and sometimes especially when the level is tightly controlled, regardless of how it was tuned, it is likely that the underlying disturbance and resulting variability is amplified rather than attenuated. That is never a good thing.

Lou notes that control loops are meant to control low-frequency disturbances. High frequency variability such as some flow loops can be reduced through the use of surge tanks or other vessels in the process. Lou writes: Continue Reading