How Should Control Loop Performance Issues Be Prioritized?

    Align the Approach for Prioritizing Control Loop Performance With Existing Automation Practices

    There are many paths to Heaven or so the saying goes. With a growing array of automation technologies, such a philosophical expression can be applied to process control and plant-wide optimization. Whether the goal is focused on uptime, throughput, or quality, control loop monitoring and diagnostic solutions provide meaningful insight into a facility’s performance. The insights gained from these technologies enable practitioners to proactively address bothersome issues before they become costly problems, and lead somewhere other than Heaven. Still a question remains: How should a facility prioritize its control loop issues? As with most engineering questions, the answer depends. It can differ from one location to the next based on the maturity of the facility’s automation practices and the experience of its staff. It can also vary based on the responsibilities of those staff, whether they’re in production, engineering, or maintenance. Some loop monitoring solutions include tools that support a variety of prioritization methods, catering to the end-user’s unique situation and goals. Approaches for prioritizing control loop performance issues include the following:
    • Change

    Change is rarely a good thing. It indicates that something is no longer performing as intended. Whether relative to the previous day, week or month, identifying control loops that demonstrate the greatest degree of change allows practitioners to isolate the source of change as time progresses. Correcting these “troublemakers” is often a good approach for facilities that have advanced automation and optimization practices.

    • Economics

    Not all loops are created equal. There’s the “bottleneck” loop that can restrict throughput, the “start-up” loop that can slow batch cycle time, among countless others. Although a precise value may not be known for each of them, these PID control loops drive a facility’s profitability. Most CLPM solutions assign an economic value to each loop, allowing those loops with the greatest impact on profit to rise to the top when their performance slips. It’s assumed that all manufacturers are mindful of their bottom line. That said, this approach lends itself to facilities with limited resources and basic automation practices in place.

    • Automation

    The core value proposition of automation is that it allows for more effective and efficient control of complex production processes. When automation investments are not being fully utilized, production is presumably less effective and efficient. Identifying loops that are not operated in their “normal” mode is another approach for manufacturers. Those facilities that are in transitioning (either from basic to moderate or moderate to advanced automation practices) tend to benefit most from this approach.

    • Variability

    The negative effects of oscillatory behavior unfailingly infiltrate downstream processes and undermine control. The effects touch on production in terms of both output and quality, and they unnecessarily accelerate wear and tear on costly process instrumentation. Correcting the performance of excessively dynamic loops is often a quick win for process manufacturers. For that reason this approach is ideal for facilities with basic automation practices, but those with moderate and advanced practices also benefit from timely corrections associated with sudden increases in variability.

    • General

    Loop monitoring solutions typically base their overall health metrics on a composite of KPIs. It incorporates performance attributes associated with control loop tuning and the relative health of the loop’s final control element as well as reflects relevant economic attributes and the process strategy in general. This approach to prioritization often results in the identification of loops with a variety of issues and no clear culprit. Although this method is suitable for all types of automation practices those facilities with advanced capabilities tend to benefit most, they have the resources to address more subtle changes in process dynamics and to benefit from their correction.

    Most CLPM technologies such as PlantESP support an array of approaches to issue prioritization and resolution. In so doing, they assist process manufacturers at each of the stages of their automation practices, from basic to advanced. Clearly improving control and optimizing PID loop performance is not a one-time event. Flexibility in your choice of CLPM solution assures that you have an appropriate path to Heaven.