I was asked the question, “Why do we need a SCADA and an MES system, as they both provide visualisation of the process to the user?” The answer involves understanding the five levels that describe the electronic/ software components used to monitor and control a production facility.
From the lowest level upwards, these are often defined as:
5: I/O: The wires, sensors, and devices that are associated with equipment. For example, devices might turn on and off as sensors measure what is happening.
4: PLC/HMI: Local screens and dedicated computers monitoring and controlling the equipment to which they are attached.
3: SCADA: Supervisory control, monitoring, data acquisition and short term data storage.
2: MES: Long term data storage and analysis. This layer is the gateway between the industrial systems and the enterprise systems.
1: ERP: Corporate administration and operations, customer orders, material acquisition…
These layers often meld into each other. As such, certain functions could be done at multiple levels but are better executed at the appropriate level. It is also theoretically possible not to implement any layer (except the control layer, as you need to have a connection to the device or sensor if you are going to measure or control it automatically).
Many current production processes do not include the top two layers (MES and ERP), leaving a massive disconnect between corporate or business processes and the factory floor. Business decision-makers do not have accurate and timely information to make informed decisions about production. Historically, people favour systems that they are more familiar with. As the people who control the budgets are more familiar with the financial and sales systems (ERP), they will invest a lot of money (millions) attempting to use these systems to make production decisions.
Can you get away with not implementing all layers? The quick answer is yes, but the best answer is no. Software and hardware are typically designed and proven to do a particular task at a particular level.
Can visualisation of the plant process at the factory floor be achieved with an MES system as well as it can with a SCADA system? I see this as the same question as, “Can tables of data be presented within Word as well as they can in Excel?” The answer is to a certain level they can, but they do it differently with a different purpose.
- SCADA is best at real-time visualisation of process and short-term historical data. They are designed to work closely with PLCs and plant floor operators.
- MES is best at presenting aggregated or consolidated data, e.g. Daily reports. It is designed to work with data repositories such as historians and corporate databases. For us, the ideal MES system has no GUI with all human input conducted at the appropriate operational level, i.e. ERP (administration) or SCADA (operations), all transactions between the two levels being handled by the MES.
If you have any questions about implementing MES and/or SCADA in your environment, please contact us at contactus@mescon.com.au
