The fundamentals of a Control System include measuring an error signal and then adjusting the system to reach the desired course or outcome. If the system deviates too fast and the control system is unable to adjust the course or outcome, the Control System is inadequate to manage the disturbances.
Some basic examples of a control system include a cruise control in a motor vehicle, temperature control in a building, the chemical concentrations in drinking water, the speed of a conveyor belt in a process plant.
Control Systems are used in domestic applications, general industry, military and virtually every modern vehicle in the world. Control Systems are very common in SCADA and Industrial Automation systems.
Control Systems are used in Industrial Automation to regulate how devices operate in real time. In a closed-loop control system the controller (RTU, PLCS, DCS) feedback (error) signal is used to adjust the control variable such that the process is constantly trying to match the operational set point. The system described here is generally referred to as a control-loop. The controller must have a suitable dynamic response to be able to adjust the system to remain stable. If the controller is unable to adjust to a stable condition (ie with minimal hunting) the control-loop is said to be “out of control”. In very complex processes a single closed-loop control system may be insufficient to stabilise the process. Cascaded control-loops may be used in situations where there is moderate complexity and the process is “changing quickly” in respect to time, however Advanced Process Controllers may be required for slow moving processes like distilling, bio-reactors etc.
A control system makes decisions about how a discrete, continuous or hybrid processes function, generally ensuring processes operate within appropriate parameters, safely, at an appropriate rate and within required quality. Control systems help factories and facilities produce quality goods safely and efficiently. Open-loop control is when the output (decision) doesn’t feed back into the control loop. Closed-loop control uses the output to influence, or provide feedback for, the next decision. Control systems can include hardware and software for programmable logic controllers (PLCs), programmable automation controllers (PACs), embedded systems and edge computing, dedicated controls, proportional-integral-derivative (PID) and advanced process controls (APC), along with distributed control systems (DCS), supervisory controls and data acquisition (SCADA) and other controllers, such as industrial PCs (iPCs).
Today’s process manufacturing plants are under a lot of pressure. These plants are often using control technologies that are 20 to 40 years old. In many cases, the control system is reaching end of support, which can lead to many problems.
Supply chain issues make it harder to find replacement parts for aging control systems, generating long lead times and extended outages. Support, when available at all, is often limited, and a shortage of personnel experienced with legacy systems means long wait times for help. Many of the best practice safety and efficiency features automation technologies provide are either difficult to connect or not available with legacy control systems.
All these problems are compounded by the corporate office calling for better performance, higher efficiency and more sustainable operations, which are difficult to achieve without the right automation technologies. As a result, many plants are looking to modernize control systems, and many are finding new technologies provide greater choice without breaking budgets or creating extended operations outages (Figure 1).
Figure 1: Modern automation technologies, like Emerson’s DeltaV distributed control system Version 15, bring a wide array of advantages over legacy systems, providing fast return on investment. Courtesy: Emerson
The modern plant is very different from common facilities of just 10 short years ago. Today’s plants no longer have a deep bench of experienced personnel who can intuitively diagnose and manage operations and maintenance issues. It will be a long time before today’s new plant personnel have that level of experience and intuition.
As a result, successful plants rely on decision-support technologies built into automation. Modern control systems are designed to intuitively integrate the automation solutions that make plants safer and more reliable. Today, pervasive sensing components monitor each asset in the plant to ensure it will at peak performance. These components send collected data to operators in the control room, along with actionable advice to keep processes running at their best. Alarm management software eliminates alarm floods, keeping plant personnel safer, while helping them avoid environmental incidents. Advanced process control (APC) helps lock best practices into the system, so units and plants run at their best, regardless of the experience level of operators (Figure 2).
All these technologies and more help plants run at peak efficiency, which helps create a competitive advantage. But they also are all difficult – and sometimes impossible – to implement with legacy control technologies. For this reason, many plants are looking to modernize control systems to take advantage of the easy integration provided by modern automation, but to do so, they must often look past traditional modernization methods to more affordable and efficient solutions.
Figure 2: Modern control systems make it easy to take advantage of automation technologies that are now considered manufacturing best practices. Courtesy: Emerson
Operations teams know control system modernization is the answer to many of the problems they face in the plant, but many teams face a conundrum; the control system with the features they want and need is from a different automation supplier than the legacy control system they have in place. Changing control systems often means rewiring and replacing the I/O, which is a time-consuming, expensive and error-prone process that also extends outages. Project teams often struggle to build a business case for the modernization they need in the face of tight capital expenditure (CAPEX) budgets and limited tolerance for extended production outages.
Because it requires the re-termination of thousands of wires and replacement of dozens of system cabinets, the replacement of existing I/O can be expensive, time consuming and risky. Every person committed to manually transitioning I/O to a new control system is someone not focused on other valuable tasks in the plant. The fewer people committed to the task, the longer a cutover will take, leading to an increase in lost production.
In the past, the only solution to this problem was incremental upgrades from the same control system manufacturer, which is still time consuming, but less so. But such a strategy is unlikely to deliver all the best practice technologies a team needs, and leaves plants “locked in” to a single vendor every time they want to upgrade, regardless of whether or not that vendor offers the required technology and support.
Today’s I/O technologies offer companies choice and flexibility in control system selection regardless of the legacy technology. Today’s project teams can choose an I/O-agnostic interface to connect a new control system directly to legacy I/O without the need to rip and replace old wiring and terminations. An I/O-agnostic interface can reduce the downtime and complexity of modernization while also reducing CAPEX costs.
Traditional modernization projects often require large project teams with many personnel on the ground to transition old I/O to new I/O before a new control system can be brought online. Often, the number of terminations that must be converted numbers in the tens of thousands, which can take weeks or months of manual labor, depending on the size and skill of the transfer team.
Using I/O-agnostic interfaces, project teams eliminate the need to transition legacy I/O before starting up the new control system. Instead, an I/O-agnostic interface operates as a bridge between the old components and the new control system. The team only replaces the existing controller and operator interface components, connecting the new controller via a communications cable that connects to the I/O-agnostic interface. Using this strategy, the project team can choose the scale of its modernization: controller-by-controller, console-by-console, or by facility area (Figure 3).
Traditional modernization of a plant with 20,000 I/O controlled by 50 controller nodes might take months or years. The process would require dozens of technicians tracing, replacing and re-terminating wiring over many hours.
Leveraging an I/O-agnostic solution can dramatically cut modernization time. The project team can instead replace controllers individually, leaving the legacy I/O in place to gain all the benefits of modern control without the cost and hassle of a full rip-and-replace overhaul.
Figure 3: I/O agnostic solutions, like Emerson’s DeltaV IO.CONNECT, provide a path for process manufacturers to adopt the newest control technologies from their supplier of choice, without replacing existing I/O. Courtesy: Emerson
No project team has unlimited budgets, but as plants face increasing pressures to improve throughput, efficiency and sustainability, today’s project resources are often even more limited than they used to be. Teams have other critical projects drawing from the same funds, and every dollar spent on modernization is a dollar unavailable for other initiatives.
Many project teams are finding I/O-agnostic solutions provide them the fiscal flexibility they need to complete modernizations without derailing other critical initiatives. Instead of one massive capital expenditures (CapEx) spend on ripping and replacing old I/O, the team instead leaves I/O in place, removing that cost from the project budget.
Because the I/O-agnostic interface empowers the team to cut over I/O on its own schedule, they can choose to transition legacy I/O after the cutover, while the plant is operational. This strategy moves I/O change to the operations budget, and it can be part of the budget for as long as it takes to complete cutover.
The act of modernizing the control system is often a money-saving choice in itself. The cost of supporting legacy systems is often high. Few companies maintain a deep bench of personnel with experience in decades-old control technologies, and even when those experts are available, they’re often expensive and only arrive after long waits, which is an expensive proposition if a unit or plant is down because they’re waiting for a technician to arrive.
Moving to a modern control system gives the plant access to a much wider range of available support personnel. Whether the plant is hiring new technicians who will have been trained on the newest control technologies or relying on consultant support from a trusted automation provider, support of modern systems is often more available, efficient and cost effective.
Consider an enterprise with hundreds of thousands of I/O points across the fleet. Modernizing the whole system would be an overwhelming undertaking and unlikely to get started even if necessary. In such a situation, implementing an I/O-agnostic solution lets the organization move all its plants to new, efficient and effective control technology while leaving the costliest element to replace – the I/O – in place.
The organization not only gains the financial benefit of transitioning I/O gradually over the next 5 to 10 years as part of the operations budget, but they also gain the advantages of the new control technologies for better performance, and higher throughput, making it easier to meet higher benchmarks and generate fast return on investment.
In a world of tight budgets, short staffing, and increasing needs for continuous manufacturing, modernization projects can seem out of reach. Sometimes, it can seem as though keeping legacy systems running or slightly updated – is the only solution.
The truth is I/O-agnostic interfaces are changing the paradigm of control system modernization. Today’s plants can reap the benefits of best-practice technologies like alarm management, advanced process control, predictive maintenance and more while leaving existing I/O in place. This helps eliminate a large percentage of the costs, time and risks associated with modernization.
Aaron Crews is global director of modernization at Emerson. Edited by Chris Vavra, web content manager, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.
Keywords: control system, I/O systems
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http://emerson.com/ioconnect
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