SCADA v MES

Supervisory Control And Data Acquisition (SCADA) is outgrowing its traditional role of coordinating plant floor processes, now offering capabilites once the reserve of ’bigger’ control systems, such as DCS, and of those linking plant floor processes into business management tools. A particular overlap is in the space currently occupied by manufacturing execution systems (MES) that document, manage and report production processes in real time and link these activities to business processes such as work orders, receipt of goods, shipping, quality control, maintenance and scheduling.

A good SCADA can fulfill many real-time important tasks at process level, such as traceability, data acquisition, reporting, secure user management or maintenance management, says Duncan Fletcher, MD of Copa-Data UK. And, as ERP (enterprise resource planning) systems cover a wide range of business-level requirements, from order management, bill of materials, and schedules, to production planning, he challenges, “what do you need an MES for?”

Process plant operators should establish if they really need a full, dedicated MES system, argues Fletcher. Often, he said, what is really required is a SCADA/control system with MES functionality to carry out certain performance calculations, with the information, such as OEE data and relevant KPIs for a section of responsibility, provided on local screens.

“If the SCADA/control system has ERP connectivity that can be implemented by the customer then the requirement for a dedicated MES system is usually reduced dramatically. Most SCADA/control systems today include some sort of database connectivity, which is also of great help,” Fletcher explained.

On the flip side of the argument, Kevin Stembridge, information solutions sales executive - EMEA at Rockwell Automation, highlights the value of MES as an “enabler” for the operator’s daily activities. “The information provided through the MES can enable the operator to take decisions while production is taking place.

“If an operator has to add material to a batch, the status or quality of that batch can be verified before the material is added. In some instances materials or batches can be quarantined by the quality department and this can be communicated immediately to the operator through the MES.”

Drive compliance

An MES, continued Stembridge, will drive process compliance. The operator’s interaction with a process can be managed by enforcing rules of production, so reducing the risk of error and simplifying tasks into manageable activities.

Furthermore, he added, an MES can ensure error- proofing in production. The steps driven by an MES guide an operator through the process. Check points built into the process then ensure the batch being produced is made within specification, using the right materials and by the right operator.

While customised SCADA applications can be built to drive operators through production and to record information accordingly, these lack the breadth offered by an MES system, believes the Rockwell executive. “A SCADA application can be effective in an automated environment, but quickly becomes redundant in manual operations.”

For Bernard Cubizolles, global market development manager, automation software at GE Fanuc Intelligent Platforms, MES applications give plant operators real-time information and control of their processes, especially in the areas of performance and quality management. “As the demands on manufacturing increase and companies look to drive costs out of their operations, decrease their energy usage and so forth, tools like these will continue to increase in importance,” he forecast.

At the process level, Cubizolles said SCADA systems continue to evolve and extend their value proposition to the operator. “Our aim at GE Fanuc is to extend the functionality of the traditional HMI/SCADA by providing the operator with advanced analysis tools for making informed, and thus better, decisions. We offer instant analytics at the operator’s finger tips through add-on applications to the existing HMI/SCADA system.”

Find bottlenecks

At newcomer Products4Automation, company founder Paul Hurst, who was previously UK managing director of Citect, comments that in today’s manufacturing facilities the need is to get more data in real time to reflect what the plant is actually doing. This enables operators to alter processes, find bottlenecks and better understand why the plant may have stopped, and then allow them to improve productivity.

“A SCADA system is a visualisation tool that was really developed for operators to see what is happening within their plant and make changes to the way the production works by allowing manual operations,” commented Hurst. “SCADA systems have evolved to enable communications to MES systems by passing data through. The need for graphics in an MES solution is limited as the production people are interested in data and not necessarily the operations of the plant.”

The main alternative to MES, though, is to develop a bespoke system, said Hurst. These, he noted, are often based on products such as Excel that tend to grow to a very large size and can become unmanageable. Also, bespoke systems cannot be modified as quickly and easily as the need for production changes.

However, when it comes to the business case for investing in either a separate MES system or a SCADA system with MES functionality, Fletcher of Copa-Data insists that to justify the purchase and implementation of a dedicated MES, it would have to be proven that the SCADA/control system does not have the capabilities to carry out the required tasks.

“The costs of implementing a separate MES System can often be prohibitive,” said Fletcher. “This usually requires a complete set or suite of software with all of the connectors to connect both to the lower level control equipment and systems as well as to the business level systems.”

Extra staff needed

Another factor can be the extra staff and training needed to implement and maintain the extra level of software, continued Fletcher: “If the MES functionality is implemented in the SCADA/control system, the costs will usually be a lot lower as the functionality will be provided by the base SCADA system, or modules that can be added to the system.

“All of the lower level connectivity already exists, all that is required is connectivity to the business systems. If the SCADA system already exists, then the training required is usually minimal as the system is already being maintained.”

At Rockwell, Stembridge noted that a SCADA system is generally deployed in isolated situations where automation control is implemented, for example on the production floor. “However, an MES is designed to cover a broader area than the production floor,” said Stembridge. “The MES functionality can be extended to the quality, maintenance or even scheduling departments.

“In addition, it makes sense to extend an MES to areas that require manual operations or activities where the implementation of a SCADA is not required. For example, the activity of cleaning a production room before processing can be tied to an order/product and driven by the MES, even though there is no automation system involved in the activity.”

Moreover, noted Stembridge, SCADA systems were traditionally designed for real-time monitoring and control, so historical data collection is generally not their core functionality. An MES, he said, provides the capability of storing summarised and event-driven data to provide a view on how production took place, both in real-time and historically.

Another point to remember is that SCADA systems may have some MES capabilities - like GE Fanuc Proficy software does - but not full-blown MES functionality, noted Cubizolles.

“MES, as a general term for the ’level 3’ software space, delivers execution, intelligence, quality and compliance capabilities not found at the SCADA level. A customer on a ’process excellence’ journey will find value in SCADA applications, while a customer on a plant or enterprise-level ’operational excellence’ journey will turn to MES solutions.”

Integration projects

Looking at the broad requirements for integrating process control systems from the plant shop floor into the IT/ERP space, the view from Copa-Data is that the main task is to ensure a good, reliable connector between the SCADA and ERP systems.

“If this connection is a standardised connector that does not have to be implemented with bespoke code, then so much the better,” said Fletcher. “This means that few man-hours are required to set the system up. It also means that further changes to the system can be implemented much easier and system maintenance can be carried our easily.”

For his part, Cubizolles of GE Fanuc, noted that in recent years, companies have invested huge amounts of money in the implementation of ERP systems. At the same time, the focus at the shopfloor level was more on execution than on connectivity to the rest of plant and to the company information systems.

“However, in order to effectively streamline the supply chain, complete vertical integration, from the shop floor to the ERP, is required,” Cubizolles explained.

“Therefore, the first step towards a successful integration resides in the connectivity of all parts of the plant. Getting rid of the islands of information is a pre-requisite. Manual operator interventions, not necessarily linked to an automation system, also need to be recorded in order to get a complete picture of what is happening on the plant floor.”

The challenge is to clearly define the information flow between the ERP and the plant floor, added Cubizolles. “What information is actually required from the ERP and what information should be retrieved from the factory?”

Standards play an important role in this, he added. The primary goal of the ISA-95 standard, Enterprise Control System Integration, is to help define what crosses the ’boundary’.

“Using standards will not only ensure better connectivity and seamless integration between the different systems,” said the GE Fanuc executive, ” but also provide the user with the certainty that his assets will be protected over time, as well as connectivity to future systems and seamless upgrades.”

For Hurst, the fundamental challenge with any integration project is to understand the customer’s process and what the company needs from the MES system. Armed with this knowledge, he said, you can ensure that both the production and product are in tune, and can be quickly altered to changes within the process.

“MES to me is a global three-letter acronym that puts all software under one heading that is between a control system and ERP,” the P4A founder concluded. “We have launched a product that fits in to the MES known area but we are calling it ’Production Intelligence’, as this describes best what customers actually need.”