Greg: I had the opportunity to talk with George Buckbee, the General Manager at ExperTune Inc., the supplier of software for loop tuning and analysis. I was always impressed with George's knowledge and his dedication to helping ISA. George worked many years at Proctor & Gamble followed by a career Sanofi-Aventis before ending up at ExperTune. George brings a lot of the user perspective and experience to his job of helping plants improve their loops.
Stan: What are you seeing in the field?
George: Control loop performance is more than just about tuning. There are huge opportunities. About 20% of control loops are in manual. This is an incredible waste of investment. The cost of a loop is about the same as the cost of a car if you consider the entire design and installation cost. Having the loop in manual is like having the car parked in the driveway. You need to get the car out on the road to deliver results. The same is true for a loop. It is frustrating for management to see an investment not leveraged.
Also, we are seeing a big shift in the needs of plants. Retirements, downsizing, and skill losses have changed what is required. In the past, engineers wanted more and more sophisticated technical tools. Today, there is a higher demand for turn-key services to improve plant performance. ExperTune's acquisition by Metso Automation has made it very easy for us to shift into a services mode, and helps us to have more of a global presence.
I have seen many Distributed Control Systems (DCS) replaced and yet the performance of the plant is the same. Many companies spend millions on upgrading control systems and don't use readily available tools to measure if automation system is doing its job.
Control loops in manual can be safety issue such as those making sure the process does not exceed the operating limits of equipment. A level, pressure, or temperature loop in manual can cause a catastrophic equipment failure and hazardous release.
As an industry, we have kind of accepted 20% as the norm. How comfortable would you be if a pilot was only using 20% of an airplane's control systems? What if the air fuel ratio or hydraulic pressure controllers were in manual?
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Greg: We put extensive effort into the necessary job of meeting project budgets and schedules often at the price of simply doing what has been done even repeating mistakes neglecting the real goal of improving process control. Since this is fall and football is on my mind, maybe this is like a football team with new uniforms and a new stadium that has the same old plays and doesn't improve the yardage gained or points scored.
Stan: Given that the loop is not in manual due to legitimate reasons such as shutdowns, startups, transitions and sequences of the unit operation, what are some of the reasons loops are being inappropriately put in manual?
George: Great point. A controller in manual is usually the symptom of some other, underlying problem. Operators will not run a loop in auto if the operator sees the plant as worse off. The operator knows the plant suffers but not how much or why. The goal is not just to get loops in auto but rather to find out what was the cause. Loops in auto may have caused oscillations upsetting other loops due to noise, interactions, backlash and stiction, and improper control strategies besides tuning.
Stan: How do you find the culprit?
George: We have a target rich environment. We have to automate the diagnostic analysis, and also to prioritize among them to find the most important root causes. We do a power spectrum analysis and take a closer look at the 3 highest peaks and see what they have in common in terms of frequencies. In the process we clean-up the data and eliminate misleading information. We look at the wave shapes. Sharp corners such as square waves and sawtooth cycles (ramps up and down) are symptomatic of discontinuous responses from hardware issues. The further downstream you go, the more these oscillations are smoothed out and attenuated by tanks. So the sharpest oscillations are in many ways a good clue as to the source of the problem.
Greg: Normally we associate these sharp responses with backlash and stiction in control valves but they can be caused by poor resolution of speed input cards for variable frequency drives, extended at-line analyzer cycle times, poor resolution thermocouple cards in a 1980s vintage DCS, improper wireless settings, data historian update time and compression settings that are too large, and actuator designs meant for on-off valves. Don't get me started.
Stan: We don't want to get Greg started so let's get back to how do you gain additional knowledge?
George: With so much data history available, we can use engineering rules to find more opportunities. We look for naturally occurring bump tests and automatically develop tuning. We notify operations only of the there is a big change in the tuning settings. Some users have no experience so you need protections against common mistakes like using data from a bump test during a load upset.