Control Training for Instrument Technicians

Control Revelations for Instrument Technicians

A four-day ProControl training class

This course upgrades Instrument Technicians' skills to a level matching the credit-capture potential of modern Digital Control Systems.

Attendees should be Instrument Technicians responsible for loop tuning, basic control loop configuration, and related communication with Advanced Control Engineers.

This class closes all the critical-skill gaps listed in the section below, leaving Technicians with practical knowledge that many Advanced Control Engineers currently lack.

Why educate Instrument Technicians?

1) Practical PID controller tuning is an ill-defined art, not a science, to most control professionals – including Instrument Technicians. After all the trial-and-error guesswork is over, the likelihood of a Tech leaving with a non-optimally-tuned loop is high; this is especially the case when a Tech’s been exposed to classical tuning methods such as Ziegler-Nichols (and many others) which ignore real-world constraints on permissible valve motion. The consequences of unscientific trial-and-error tuning compound as loops become more essential to plant profit, since loops with the highest economic return are typically also the toughest to tune.

A few examples of other PID-related gaps: a) Technicians (along with most Control Engineers!) typically mistrust the Derivative mode in a PID controller, with stability of the most sluggish (and most profitable) process loops suffering as a result. b) The need for significantly different tuning between Interactive and "Ideal" PID algo's, structural alternatives available in most DCS systems, is almost always unrecognized. c) The rationale behind which levels to tune tightly, and which to tune loosely (to minimize flow swings) – then how best to achieve this tuning – is another mystery, and d) The merit of a Proportional-on-Error vs. a Proportional-on-PV PID structure is almost always viewed incorrectly.

2) The fastest and easiest way to tune a PID loop “from scratch” is to run an open-loop plant test, to express the outcome in just a few process parameters linking changes in PID output to subsequent changes in PID input – then to obtain optimal PID tuning from this process understanding, at a mouse-click. PC-based software exists to convert process data into the simple process parameters needed for loop tuning, with usage fully comprehensible to both Instrument Technicians and Advanced Control Engineers.

Almost no Instrument Tech uses anything other than seat-of-the-pants tuning, which takes many iterations to “get right” – whatever that means!

3) When a Tech’s called to retune a troublesome loop, ‘Standard Procedure’ is to retune it by some seat-of-the-pants method, then to walk away. (Most Control Engineers do the same thing!) While this band-aid approach may be great for job security, it’s not great for the process in the long run, since the most common reason for a loop’s tuning “going bad” is that something has changed in the process. Since nothing’s been learned about this, when the process changes again, e.g. back to where it was yesterday, the tuning again “goes bad”, and we’re doomed to repeat our seat-of-the-pants correction, when / if alerted by the Operator. But since callouts by the Operator arise more from swinging loops than from sluggish loops, the net result are loops which are detuned on average, at cost to the plant’s higher level controls (such as DMC).

In contrast, the correct answer is to re-understand the process at its current operating point per the procedure in (2), using a tool which saves not just new PID tuning, but the new process parameters behind this tuning. Our Instrument Techs are trained to translate the resulting growth of process understanding over time into adaptive tuning which always yields optimal loop response, eliminates need for callouts, and keeps DMC setpoint-change-based models at peak performance.

4) Communication between the Technician and Advanced Control Engineer levels may not always be optimal. Yet more reliance must be placed on this link as Engineers are asked to achieve still higher sophistication – which must rely on all lower levels being rock-solid, and yielding predictable setpoint-change response. Requesting Control Engineer help (when needed) in implementing the adaptive control above is an example of communication promoted by good Instrument Tech education.

5) Most Instrument Technicians know much more about hardware than about the process being controlled – and they often stumble when requesting the process changes needed to improve PID tuning. The fix is practical training on both open-loop and closed-loop plant tests, with a heavy dose of real plant data, and testing pitfalls, added.

6) PID tuning derived from process understanding must be tested, and occasionally improved, via a setpoint-change in closed-loop. While this claim may seem far-fetched even to experienced Advanced Control Engineers, our graduates will always make the directionally-correct move on the most “needy” P, I, or D tuning constant, and will further make directionally-correct simultaneous moves on these constants when warranted. (We have hundreds of testimonials saying the tuning we teach truly is a Revelation.)

7) If Techs have a role in loop configuration, their motivation to deploy even elemental degrees of loop sophistication, such as cascade or feedforward control, may be low – since the process reward for putting in more configuration and tuning effort isn’t clear. Investment in potentially money-making computer control hardware is then underutilized. We cover a highly-motivational cascade example in-depth … and, time permitting, add a short but spectacular war-story on feedforward’s objectives and benefits.

This Course gives Instrument Technicians comfort and competency with:

1) Both steady-state and (especially) dynamic characteristics of typical Refining and Chemicals processes. Examples: furnaces, drums, heat exchangers, and towers. Experience indicates this is a critical gap in the working knowledge of most Technicians.

2) How plant testing, and loop tuning evaluation, can be done without "rocking the process boat" -- whether by changing a control valve position directly, or by changing the setpoint on a loop. How to avoid common, practical pitfalls when conducting plant tests aimed at improving loop tuning – in both open and closed-loop. Use of a computer tool to arrive at the process understanding required for one-step loop tuning, using realistic (i.e., non-step, noisy, unevenly-spaced) process data collected from a plant test.

3) How to tune simple primary-to-valve loops such as flows, temperatures and analyzers by ProControl’s highly-acclaimed mode-balance and loop-strength procedures NOT utilizing the process knowledge gained in (2).

4) How the simple process understanding gained in (2) eliminates need for any guesswork in loop tuning, and significantly reduces tuning time and effort – typically by 75% vs. (3). Use of the computer to yield the best PID constants in one step for any process loop, on any DCS system. Why process behavior can have a large impact on loop stability, and on optimal P, I, and D parameters. Why control loops "go bad".

5) Why level and pressure control is a world apart from flow and temperature control. Which level and pressure loops to tune quickly. In contrast, how to tune levels to maximize surge-capacity utilization -- i.e., to minimize downstream flow disturbances.

6) Why cascades are desirable -- as graphically demonstrated by before/after case studies. Tuning cascades in both open and closed-loop modes, using process understanding to save time. Potential cascade pitfalls, and solutions.

7) Real-world problems in tuning and maintaining a variety of loops: drifting process behavior; sticky valves; unmeasured disturbances; measurement noise; excessive signal filtering.

8) Time permitting: Why Advanced Controls are important for stabilizing operations and increasing plant profit. What feedforward, constraint and multivariable controls attempt to achieve, and just enough on HOW they work to clear up any mysteries. Why simple controllers may cycle on an interactive distillation tower; briefly, how Advanced Controls (such as DMC) help. How plant economics dictate control objectives.

Instrument Technician Course Prerequisites?

NO math or previous control background is assumed, nor needed. Textbook control theories of no practical use in a real plant (e.g., frequency response techniques) are simply not presented. Textbook tuning strategies (e.g., Ziegler-Nichols; Cohen and Coon) are briefly considered, then rejected for the heavy-handed moves they produce in an interactive process plant. We replace all such typical control nonsense with practical, common-sense insights and procedures understandable to complete novices and non-professionals. Since we strip away all misconceptions and myths, and build full understanding from scratch with no theoretical underpinning, there are no prerequisites for any ProControl course.

Questions? Please call ProControl at: 303-670-8492 (office), or: 303-670-9092 (cell).

Or … please e-mail ProControl’s founder and CEO, Bob Bartman, at: bob@procontrol.net.