Questions from plant manag­ers

Process Optimization

Michel Ruel answered a number of questions frequently asked by plant managers.

 Question 1
An engineer at our plant claims that in one specific area, oscillations are normal. Does this make sense?
Simple answer: No, absolutely not!
Detailed answer: This may be an equipment problem, a tuning issue or programming. Put all loops in this area in manual mode and the oscillation will disappear. Troubleshoot the problem.

Question 2
We need to improve performance in one area. Our engineers attended a seminar and want to implement Model Predictive Control. Is this the right approach?

Simple answer: Can't say
Detailed answer: Before deciding on the right approach, an audit is necessary to benchmark process, controls, equipment, etc. The result of the audit will determine the roadmap, including the need for advanced control and the right approach. The audit will be finished within a week and cost less than $20,000.

Question 3
We plan to tune loops in one area. What level of work does this entail?

Simple answer: Days to weeks, not months
Detailed answer: Tuning loops is easy; one can tune more than 50 in a day! But that is not the way to go. When modeling the processes using modern tools, many loops will be problem-free and these can be tuned quickly. Others with valve problems, configuration problems or process problems will require more effort. Typical numbers are 40 loops/week/person.

Question 4
What percentage of loops should be in automatic (or cascade) mode?

Simple answer: 100 %
Detailed answer: This may be acceptable for a short period of time, but over the long term, it should be above 95%. We prefer to measure whether the loop is in the right mode AND not saturated (within range) AND the process is active (e.g. pump is running for a flow loop).

Question 5
What percentage of loops should be stable?

Simple answer: 100 %
Detailed answer: A loop is stable if it is not oscillating and if the valve has no stiction. An exception is level loops where the tank acts as a buffer and we let the level fluctuate to absorb variability.

Question 6
How many alarms can an operator handle under normal conditions?

Simple answer: 6 to 12 per hour
Detailed answer: ISA Standard 18.2 explains this in detail. To reduce the number, we have methods to benchmark, detect the bad actors, establish priorities and remove chattering and predictable alarms.

Question 7
How long does it take to train technicians and engineers to troubleshoot, tune and optimize control strategies?

Simple answer: 3 to 5 days
Detailed answer: We recommend a workshop where they will be exposed to typical problems: ME-200-3. After those 3 days, we recommend 2 days of hands-on practice during which real problems will be solved, thereby covering the cost of training.

Question 8
We have too many alarms. What should I do?

Simple answer: Alarm rationalization project
Detailed answer: See the article on Alarm Management

Question 9
In Alarm Management, removing bad actors will reduce the number of generated alarms by what percentage?

Simple answer: 50% or more
Detailed answer: Typically, by more than 50%. To achieve this we benchmark, then analyze the top-10 most frequent alarms, chattering alarms and predictive alarms.


Michel Ruel
BBA - Top Control
BBA is an independent Canadian consulting engineering firm operating internationally. Its team is composed of highly-qualified experts in several engineering disciplines including electrical, civil, mechanical, industrial data processing, mining, metallurgical processes, automation, and construction management.