All of the “things” that make modern life possible are manufactured in facilities that are an interplay of machines, sensors, motion controls, programmable logic controllers (PLCs) and enterprise software.

From automobiles to pharmaceutical production, we collectively rely on this web of electronics and software to reliably manufacture the items needed to improve our quality of life. Constructing reliable Industrial 4.0 systems requires engineering teams to think about connectivity and interoperability at the start of the design process.

Security, reliability, interoperability and longevity are key pieces to the connectivity puzzle. Industry 4.0 is about more than transmitting raw data. We can use the power of the information to translate the complex web of components into actionable intelligence to keep our production systems operating at peak efficiency.

The distinction between raw data and information is an important one. Operational decisions need to be made on information, often fused from several raw data sources. Modeling information is a key part of Industry 4.0. A tool for building interoperable Industry 4.0 systems is the OPC Unified Architecture (UA).

OPA UA Fundamentals

OPC UA is an information architecture designed to enable interoperability between industrial components. Based upon a deep, collective experience in the industrial sector, OPC-UA was constructed upon several key pillars to ensure a long lifetime of open information exchange.

Information Modeling, Interoperability and Access

Many communications standards are focused on the movement of raw data. OPC UA standardizes how information is communicated. The starting point in OPC UA is a foundation of fundamental data types. These data types are assembled into arbitrary information structures that can model any type of sensor, machine or process.

OPC UA Information Modeling Framework Image Courtsey: OPC Foundation OrgFor a better experience, download the block diagram.

The OPC UA has standardized models for many common industrial machines and processes. For example, a CNC system can be modeled using OPC 40502-1. This means software can access the state of an OPC UA compliant CNC machine in a standard way, simplifying the systems integration.

CNC Standard Information Model through OPC 40502-1

Beyond the standard information models, vendors can add extensions to enable specific features for their equipment. The mechanism for accessing information is standardized in OPC UA. Vendor specific information can be discovered and queried through standardized OPC UA access mechanisms. OPC UA also enables the ability to execute tasks, or domain-specific APIs on target equipment.

There are two primary approaches for accessing information in an OPC UA system: Client-Server and Publish-Subscribe (Pub-Sub).

OPC UA Information Model Access Image Courtsey: OPC Foundation OrgFor a better experience, download the block diagram.

When the OPA UA was first released in 2008, the client-server paradigm was the primary model for information exchange. This was the result of the historical precedent from which OPC UA was derived. The client-server model is based on TCP transport and HTTP/SOAP.

OPC UA Client Server model with Request ResponseFor a better experience, download the block diagram.

The client-server model can work well in many use cases. A client needs to be in charge of the information access it requires. If several clients need the same data from a single OPC UA server, each must independently request the data. This approach can lead to a significant increase in network traffic and system complexity.

To address these use cases and access patterns, the OPC foundation added a publish-subscribe  pattern to the specification. With the Pub-Sub pattern, devices that generate information can publish to a “broker”. Devices needing access can look to this broker for specific information through “topics”.

OPC UA Pub-Sub Access PatternFor a better experience, download the block diagram.

The broker can be one of several open message oriented middleware software so as AMPQ ( ISO/IEC 19464:2014) or the common MQTT ( ISO/IEC 20922:2016) messaging system.

The important aspect here is that OPC UA defines the structure of the information such that endpoints can process information in a standardized way. The advantage of the Pub-Sub approach is that system complexity can be reduced when many devices need access to the same information.

OPC UA also defines a broker-less model for information exchange. In this model, no additional software/middleware is required.

OPC UA Security

OPC UA typically uses TCP/IP transport (both TCP and UDP) to move information. Data is secured using standards compliant methods. TCP sessions between a client and server (or with an information broker) use session encryption. This can include X.509 certificates  so both ends of the information exchange can validate that the authentication is valid. Messages can be signed such that the recipient can verify the identity of the requestor. OPC UA includes auditing functionality, such as access that can be logged to leave an audit trail.

Platform and Runtime Independence

Because OPC UA runs on TCP/IP and Ethernet, virtually any hardware with Ethernet capability can participate in an OPC UA system. It is possible to run client or server functions on a MPU like i.MX 93 running on Linux, an i.MX RT crossover MCU such as the i.MX RT1180 using RTOS or even bare metal on a microcontroller such as the MCX N947. Solutions can include high-level, powerful operating systems such as Linux. A starting point for a software implementation could be the open source open62541  or S2OPC stack.  Many commercial offerings  are also available to accelerate development.

Deterministic Communications with OPC UA and Time Sensitive Networking (TSN)

Many industrial applications require deterministic timing for delivery of information and critical control. One method to meet a deterministic, real-time requirement is via TSN Ethernet technology.

Used in conjunction with IEEE1588v2 Precision Time Protocol, TSN enables deterministic behavior by defining fixed periods of time when a node can communicate on the network without contention.

TSN was developed independently of OPC UA. However, OPC UA can interoperate on any Ethernet network. As OPC UA evolved, the foundation added cross-layer control so high priority information could be prioritized. OPC UA and TSN can work together for interoperable, deterministic systems.

NXP devices, such as the i.MX RT1180, include hardware support for Gigabit-capable TSN.

The i.MX RT1180 can be a solution for an OPC UA node. With up to 5 Gb ports, the i.MX RT1180 supports the latest TSN standards making real-time control possible in an Industry 4.0 solution.

Using NXP to Implement an OPC UA Solution

OPC UA is an information architecture built to be extensible, open and secure for Industry 4.0 applications. It enables engineers to design automation solutions that can “plug in” to a complex production scenario, simplifying information exchange. The open nature of OPC UA enables equipment that can be over lifecycles commensurate with rugged industrial equipment.

NXP offers several options to implement an OPC UA solution.

• An Ethernet-enabled microcontroller such as the MCX N947 running bare metal or using a simple RTOS such as FreeRTOS
• A TSN-capable crossover MCU such as the i.MX RT1180 running a more capable RTOS such as Zephyr
• An industrial applications processor such as the Layerscape LS1028A running Linux

There are commercial software enabled options for OPC UA  as well as open source variants  that are platform independent.