Why this article is important:
- This article introduces overall controller effectiveness (OCE) as a new, intuitive metric for evaluating PID loop performance in process industries.
- It tells how OCE helps process plant teams interpret vast amounts of control loop data by providing a unified KPI that captures availability, performance and quality in a single score.
- It shares how OCE can be applied to individual loops, units, plants or entire fleets, supporting strategic decision-making across all operational levels.
Process plant personnel have long searched for metrics to help guide operational improvement efforts. Since the 1980s, discrete manufacturers who operate machines and assembly lines have applied a generalized metric called overall equipment effectiveness (OEE) for this purpose. Now, a similar metric called overall controller effectiveness (OCE) is helping process manufacturers to direct their regulatory control optimization efforts. Like its discrete industry counterpart, OCE equips process manufacturers with an intuitive means for benchmarking control at a plant-wide level and for identifying specific areas that undermine performance and productivity.
PID control loops, which are fundamental to the automation of process plants, are increasingly a source of voluminous amounts of data useful for trending and analysis. Still, production teams often struggle to interpret the data and understand if and how their facility’s performance has changed. To fill this information gap, a leading control loop performance monitoring (CLPM) software company has incorporated OCE into its offering. With OCE, management and operations staff now have a simple, uniform means of assessing the performance of a single control loop, a particular unit of production, an entire plant, or even a fleet of facilities (Figure 1).
Production information on a need-to-know basis
John Naisbitt published his book Megatrends in 1982 and forecasted manufacturing’s current dilemma: “We are drowning in information but starved for knowledge.” That was the same year that OEE was introduced as part of a greater holistic total productive maintenance (TPM) approach to efficiency management. Though a simple metric, OEE is now nearly universally accepted. More importantly, it is credited with helping discrete manufacturers see through a growing fog of data and achieve significant gains in productivity.
At its core, OEE is a comprehensive measure for assessing the performance of a single machine, a production line, or even an entire plant. It incorporates three attributes common to all production assets and core to evaluating production efficiency:
- Availability: running, without unplanned stops
- Performance: running normally and as fast as possible, without constraints
- Quality: producing good parts, without defects
Each of these three constituent factors are calculated as normalized values with scores ranging from 0-100%, and the associated OEE value is formulated by multiplying each of the three scores together. Among discrete manufacturers, OEE values of 50-60% are viewed as average whereas values of 85% or better are considered world-class. Though OEE is not a perfect measure, it provides a consistent basis for evaluation and enables multiple insights. Engineering and operations staff can use OEE to assess the performance of a single asset just as easily as plant and corporate management can use it to benchmark the performance of an entire facility. Beyond assessments and benchmarks, OEE’s formulation simplifies finding the root cause of an issue and determining the corresponding corrective action.
For discrete manufacturers utilizing OEE, the fog has lifted. Until recently, however, process manufacturers relying on hundreds or even thousands of PID controllers have continued to struggle with answering the question: “How well is my plant being controlled today?”
Checking the status of a plant with OCE
With decades of experience in process optimization, Control Station helps process manufacturers to access and analyze their data as a means of proactively isolating trends that lead to suboptimal performance and even unplanned downtime. The company’s market-leading PlantESP CLPM solution includes a library of key performance indicators (KPIs) that assess controller attributes linked to PID tuning, mechanical operation, and process interactions. With the recent introduction of OCE, the company now equips process manufacturers with a singular metric for benchmarking performance.
Like OEE, OCE is a composite value formulated using the same operational attributes (Figure 2):
- Availability: running in normal mode, without being overridden
- Performance: controller output (CO) running within its designed range, without limitations
- Quality: process variable (PV) operating near setpoint (SP), within acceptable limits
Between the costs associated with hardware, software, and configuration, a process manufacturer typically invests $10,000 to $20,000 to implement a single PID control loop. As a result, keeping each controller working effectively in its designated or “normal” mode is essential to both maintaining availability and maximizing return on assets. In terms of performance, preventing large CO swings and avoiding operation at physical constraints limits unnecessary wear and tear and keeps production flowing smoothly. As a measure of quality, maintaining PV at or near SP during all phases of operation is often the single most important function of a PID.
When combined into a single OCE value, these different measures account for much of a PID controller’s performance. Furthermore, OCE values can be easily aggregated to account for performance across a wider range of assets, whether that be at the operating unit, plant-wide, or even enterprise level. With OCE, production staff who are generally more familiar with a PID’s operation gain an intuitive “at a glance” KPI for daily evaluations of loop or unit performance. Supervisors, managers, and corporate executives can use OCE on a weekly, monthly, or other periodic basis to gauge higher order operations and to focus optimization efforts more strategically. With OCE they can quickly check the status of their investments.
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OCE points the way toward steady improvement
At many if not most process manufacturers, loop tuning and optimization are often pursued on an ad hoc basis, often prompted when trouble arises. Considering that automation often comprises approximately 10% of a facility’s total capital cost, manufacturers are generally open to finding a better way of extracting value from their investment by improving their site’s operational performance. Growth in the availability of process data and innovative tools have created new opportunities to aid a site’s engineering staff (Figure 3).
Tools like PlantESP tap into and analyze process data that resides in a site’s existing data historian. They let engineering staff target their site’s most critical control loops. The Control Station team and partners like Daesim Technologies can provide initial deployment and ongoing support services as needed so sites can rapidly get the CLPM and OCE solution online.
Generated reports highlight underperforming loops using OCE and facilitate the assignment of weekly work orders (Figure 4). Tellingly, field experience demonstrates that OCE values for a facility tend to show a steady upward trend using this approach. That trend correlates with overall improvement in a facility’s performance, reinforcing the effectiveness of OCE as a general measure of loop performance.
Process control teams see OCE as a useful tool helping them to address non-optimal conditions which might otherwise fly under the radar. Though other metrics are valuable, OCE is an intuitive one for determining if there are issues that require investigation. Once knowledge of an issue is established, engineers can see the direction needed to drill down within to isolate the underlying problem affecting performance.
Simple and uniform performance assessment enabled by OCE
Gleaning the right amount of information is important for any situation because too much or too little can be equally incapacitating. Like OEE, OCE has shown that a generalized measure of controller effectiveness can be a powerful tool in understanding performance and directing optimization efforts.
OCE elevates just the right amount of detail to the right people. This empowers front line personnel to take corrective action, resulting in continuous improvements. It also gives organizations the tool they need to efficiently and effectively benchmark their process control performance and then compare it over historical periods or against other assets or sites. With OCE, process manufacturers can now better understand performance and deploy resources in pursuit of world-class production.
