OPC UA: A Framework For The Industrial Internet Of Things
The ISA 95 spec and OPC UA companion standard provide a model that allows software programs to exchange all the relevant information throughout a manufacturing organization. This provides the groundwork for an industrial internet of things by breaking down the communication barriers between objects.
The Internet of Things
The concept of an “Internet of Things” (IoT) has been around since about 2005 and has really begun to catch on in recent years. Basically, IoT is connecting multiple “things” with sensors to data processing programs capable of sending data to and receiving data from those things. The things can be anything from household appliances to industrial machines. In factories this concept is called the Industrial Internet of Things or Industrie 4.0. Industrie 4.0 is the term coined in Germany for the IoT because it is being considered the 4th Industrial Revolution. No matter what it’s called, the goal is to create a network world with intelligent objects that can communicate and interact with each other.
Both IoT and Industrie 4.0 involve connecting manufacturing machines and sensors so they can communicate and take action in real time. This can involve anything from automated control of production lines to maximize throughput to smart electricity grids that can balance power generation to match loads.
IoT is really just a concept, so there needs to be some enabling technology to make it a reality. There are some equipment and software vendors that have come up with their own solutions, but this can be limiting. Universal standards are required to guarantee interoperability between equipment and devices from different manufacturers. Two related specifications have been established to address the need for a standard: ISA 95 and OPC UA. When combined, these two specifications provide a prescription for implementing a universal IoT platform.
Manufacturing Operations Management Systems
Before jumping into the ISA 95 and OPC UA standards, we need to provide a little background about current systems and why a universal standard is needed to achieve an IoT environment. Think about how many different control and monitoring systems are required in modern manufacturing operations:
- Manufacturing Execution Systems (MES) for managing production
- Plant Information Management Systems (PIMS) for collecting and analyzing process data
- Laboratory Information Systems (LIMS) for tracking quality test performance
- Warehouse Management Systems (WMS) for managing the inventory of raw materials and finished goods
- Computerized Maintenance Management Systems (CMMS) for managing maintenance operations
- Learning Management Systems (LMS) for managing the training and qualifications of personnel
ISA 95 divides typical manufacturing organization activities into 5 levels.
Level 0 is the actual physical process. Levels 1 and 2 include all activities needed to monitor and control the physical process in real time. Level 3 includes all of the manufacturing operations management activities mentioned above. Finally, Level 4 includes all of the business planning and logistics activities that are required to ensure the right materials are used to make the right products so they can be delivered to customers. ISA 95 focuses on defining the information exchanges that occur within and between Levels 3 and 4.
ISA 95 defines four resource categories required for managing the information exchange in manufacturing processes:
- Materials and their properties
- Role based equipment
- Physical Assets
- Personnel and their roles and qualifications
OPC UA Information Models
OPC UA uses a flexible and extendable system to define objects and variables. Templates (called Types in UA) are used for definitions and instances are created from them. For example, a Motor (object) template might have properties (variables) HP, RPM and Voltage. If motors M100 and M200 (instances) are created from that template, they will have the HP, RPM and Voltage properties. Templates can be extended by creating a child and adding properties to the child; instances created from the child template will have all the properties from the child and parent templates combined. If an ACMotor child template adds the Phase property then motor M300 created from the ACMotor template will have properties HP, RPM, Voltage and Phase.
ISA 95 defines four base templates: Equipment, Physical Assets, Personnel and Materials. From these a user can create sub-templates that accurately represent the types of objects in the facility. Motor templates might have three or four sub-templates. Pump templates could have 8 or 9 sub-templates whereas other objects might have none. The user can create the level of detail appropriate for their needs.
Once the templates are complete the user can create the facility’s objects and combine them in meaningful hierarchies and the objects can exist in multiple hierarchies without conflict. One hierarchy might represent the physical layout of the facility while another might represent the process flow. A piece of equipment in multiple hierarchies will have information from each (such as a cost center from the physical and a grade tag from the process) but each hierarchy will only be aware of the information appropriate to that hierarchy.
The values for properties can be static and stored in a database or dynamic and driven by a process tag. Most dynamic properties are used in equipment but it is possible to have dynamic properties on other types.
The ISA 95 spec and OPC UA companion standard provide a model that allows programs to exchange all the relevant information throughout a manufacturing organization. This provides the groundwork for an industrial internet of things by breaking down the communication barriers between objects. Software can be created to allow autonomous communication between equipment and sensors, but the improvements are not limited to machines. Communication between people and things and even person to person improves. All of this can improve manufacturing efficiency, reduce costs and facilitate better, faster decision making.