Never Forget the Foundation

Regulatory control provides the foundation for advanced, supervisory capabilities. Neglect the PIDs and any visions of advanced control grandeur will quickly come crumbling down.

While I’ve been known to enjoy an occasional round of Cards Against Humanity with friends, I stick to more appropriate games when I’m with my wife and kids. When it comes to games we’ve established somewhat of a tradition in the Munroe House.

Our lives are all so busy that we reserve Sunday afternoons to spend time together. We all join in with making a meal, listening to music, talking out the week previous and ahead and indeed playing at all sorts of games. Jenga is a regular.

The rules are simple and easy for young and old to enjoy. Now that my son and daughter are older they’re craftier about which blocks to move. Even so, the Laws of Physics still apply. In the game of Jenga a strong foundation is still tantamount to success.

While those Sunday afternoons have given my children an appreciation for good food, lively conversation and competitive skills, I hope they take away that lesson about the need for a solid foundation in anything they do – both personally and professionally.

Those that have read my previous Viewpoints posts may recall that I’ve spent a good portion of my career in the pharmaceutical sector. As I’m Irish that probably comes as no surprise – nearly every major pharma company has an established presence in Ireland. While manufacturing has slowed here and in most areas across the EU, pharma has remained the backbone of Irish industry.

Indeed, as recently as 2014 Ireland ranked #7 globally for pharmaceutical exports. It’s provided a strong foundation on which the country in general has grown. Strong as it is, individual plants have occasionally forgotten the importance of their controls foundation and fallen for the allure of a new Batch or APC strategy.

At one particular pharma plant I was asked to assess a new control system with a view to optimising its performance. The system involved the use of an integrated control system with batch recipes and MES, to an S88 standard.

Unfortunately, this approach resulted in a very regimented process that did not handle process delays or upsets well. As part of my assessment I spoke with plant engineers and operations staff.

They all remarked that non-engineering managers had taken a good pitch from the OEM system’s rep and committed to the new approach. That choice was made in spite of nearly unanimous push back from those that kept the plant running efficiently about resolving some fundamental issues first. Given my references to Jenga and the need for a solid foundation, the direction of this post may be obvious.

Even so, hear me out. The PID controller provides the core for most modern plant automation applications regardless of supervisory layers. While it may not be revolutionary, it’s still the right technology for almost all automation needs.

Consider these details:

Established, Universal…and Misunderstood

• ​For decades the PID controller has been a dominant, underrated and often misunderstood control technology. It provides a highly robust, stable means for automating the control of complex production processes. That’s key to maintaining a strong controls foundation. Based on the PID’s reputation as a proven, stable technology, manufacturers across the process industries rely on it.
  
  Even so, without sufficient understanding the PID can be difficult to employ effectively. There’s a reason practitioners view the tuning of PIDs as a “black art”. In the end the strengths of the PID far outweigh its weaknesses, the PID will remain the dominant regulatory technology for the foreseeable future.

Flexible, Extensible…and Dependable

• There are many forms of the PID. Whether P-Only, PI, PID, (anyone who has attend one of my classes will know what the D stands for!!) The array of options make the PID controller a highly flexible technology that’s suitable for most industrial applications. When viewed in the context of both basic and advanced applications such as Feed-Forward and Cascade, the value of the PID is reinforced.
  
  Although APC strategies may be alluring, it’s worth first considering alternative uses of the PID. What’s more, if the decision to pursue a new Batch or APC solution is based on regulatory control challenges, then realize that those challenges will persist. Building on top of a faulty foundation is never a good idea. It’d be better to invest in your existing control scheme. The PID is dependable if given appropriate consideration.
  

Effective, Efficient…End of Story

• Supervisory control applications are built on top of a plant’s regulatory control layer. That means that any advanced strategy – MES, Batch or APC – relies on the underlying PIDs to perform their job. If a PID controller cannot reign in oscillatory behaviour or regulate settling time, then most likely the problem stems from poor configuration and/or controller tuning.
  
  Such an issue is rarely the call for increased complexity – advanced strategies are built on top of the PID…they will not replace them. The reality of the PID-Advanced Process Control relationship simply underscores the need for a strong foundation. Regardless of the supervisory technology, a plant will not function effectively and efficiently if its control foundation is flawed.

Back to that pharma project: I recommended a refocus on the PID-based control scheme. Any combined control architecture is dependent on each of its component parts operating to a standard. It’s true that interface weaknesses and poor control considerations attributed to the PID can cause glaring gaps in control.

More often than not, however, those flaws are inappropriately linked to limitations of the PID and they provide the rationale for more sophisticated control schemas.

In the absence of a well-functioning regulatory control layer any advanced control strategy will suffer a similar fate. Without a strong regulatory control foundation, a new, Batch or APC strategy is bound to tumble and just like with Jenga: You will be picking up the pieces for days!!