OPC Servers enable communication between most elements of a control system. These include OT (operational technology) products such as PLCs, PID controllers, chart recorders, cameras, analyzers, HMIs, SCADA, DCS, historians, IT (Information Technology) solutions and much more. Since OPC communications can have a significant impact on performance, quality, and reliability, the selection of an OPC Server is pivotal to creating the most competitive machine, production line, or process.
Selection criteria to consider when choosing an OPC Server include the following:
- Performance – delivers high transaction speeds and tools for performance management.
- Reliability – delivers 24x7x365 solution reliability.
- Redundancy – provides a specific method of support for higher availability.
- Technical Support – offers high quality technical support and program types.
- Northbound Protocol Connectivity – offers client support through one or more standard or proprietary APIs.
- Southbound Protocol Connectivity – provides robust support for your required protocol(s).
- Flexibility – contains features and benefits that are differentiators at a detail level.
- Proven – is used extensively in the market.
- Distribution – is available locally or globally.
- Embracing – plays well with other applications.
- Operating System Platforms – is supported on the operating systems important to you.
- Price – is cost competitive with other available solutions.
- License Model – offers license models that fit your OpEx/CapEx budget.
- Ease of Use – is designed for user or programmatic configuration.
- Vendor Endorsed – provides solution endorsement by the protocol owner.
- Certifications – meets protocol certification requirements.
Performance – delivers high transaction speeds and tools for performance management. The need to consider performance in an OPC Server will vary with the size and character of the application. Small applications will have fewer devices and can tolerate lower communication bandwidths. Many protocols offer different modes of data transfer: block transfers vs individual variable transfers. Be aware of the application's needs and the supported methods in the data transfer protocol. Look for OPC Servers that deliver the information needed but also that support status monitoring for communication errors, number and identity of clients, security parameters, system status, and more as additional valuable information.
Reliability – delivers 24x7x365 solution reliability. OPC Servers offer many types of operation for different states of operation. Considerations need to apply to both a fully functional operation and an operation when some devices are offline. Consideration should also be given to communication line quality, for example error rates in wireless configurations. Quality OPC Servers will adapt to these varying situations and recover automatically.
Redundancy – provides a specific method of support for higher availability. OPC Servers often support architectures for higher availability. These may include redundant communications paths or complete OPC Server redundancy that is invisible to a client application. High availability may also rely on hardware platforms like those from Stratus or virtual machines.
Technical Support – offers high quality technical support and program types. Is the OPC Server provider a long term viable solution provider? Are there regular releases of this OPC Server and are there updates to the latest technology, the latest security patches, and enhanced functionality? While an OPC Server may comprise a small price component of an overall solution, the OPC Server typically plays a critical role in overall system operations therefore proper technical support should be available from the installer and other companies as well. Evaluating the source provider of an OPC Server is key to long term support.
Northbound Protocol Connectivity – offers client support through one or more standard or proprietary APIs. OPC Servers will obviously support OPC APIs, but many versions and enhancements are released over time. What are the OPC Versions that the OPC Server supports? Options are OPC Classic versions of OPC DA, OPC A&E, OPC HDA, and the newer OPC UA with support for Data Access (DA), Alarms and Conditions (AC), and History Data Access (HDA). While OPC UA is a complete protocol with data structures and transport, there are even newer forms of OPC UA based on the MQTT Transport. Often, OPC Servers will support a number of Northbound APIs for use in different scenarios. Internet and IoT architectures benefit from publish/subscribe protocols such as MQTT and AMQP. SCADA architectures benefit from poll/response with reporting by exception. There are also proprietary protocols such as Suitelink and EDA (Easy Data Access) that support particular SCADA software solutions.
Southbound Protocol Connectivity – provides robust support for your required protocol(s). Southbound connectivity offers communications, typically both read and write, to the devices in your automation system. The most common protocol in the world is MODBUS, delivered back in 1979 as a serial protocol and now adapted over time to Ethernet. In the IT domain, SNMP (Simple Network Management Protocol) is quite common. In the power industry, there are protocols such as 61850 and DNP3. In building automation, there are BACnet and BACnet/SC. Various markets and vendors have introduced protocols that are adapted to best support vertical markets or unique applications. The latest technology to consider is Ethernet with TSN (Time Series Networking), supported by an industry standard protocol called CC-Link IE TSN. Other industrial ethernet protocols include PROFINET, Ethernet/IP, and EtherCAT. There are dozens of current day protocols and an equal number of legacy protocols that are supported by many different OPC Server providers. Modern OPC Servers will support more than one protocol at a time, and these are often sold as individual drivers, bundles of protocols, or a complete suite.
Flexibility – contains features and benefits that are differentiators at a detail level. Flexibility in an OPC Server can range greatly and becomes more important in larger or more demanding applications. Flexibility may involve the support of interesting architectures, runtime configuration, remote configuration, API based configuration, the ability to import and export configurations, application documentation, and more. In small and simple applications, this is not a differentiator, but in larger and more demanding applications, this can become a serious area of differentiation between offerings.
Proven – is used extensively in the market. In today’s software world, most offerings have been developed for localization (international language support). Leading solutions will be sold globally and will have operation support in various languages, both European as well as the more complex Asian languages. Your application may only need English support, but for multi-national corporations, companies that have proven themselves on the global stage are more likely to deliver long lasting solutions.
Distribution – is available locally or globally. Are the products sold through distribution or direct? Is the OPC Server solution an OEM solution for others in the industry? Is it recognized more broadly as an industry building block? In terms of market reputation, these are factors to consider in comparing one offering to the other. Most OPC Servers allow you to download a trial for test purposes prior to requiring a purchase.
Embracing – plays well with other applications. The foundational requirement of an OPC Server is typically to co-exist with other client software and applications on one computer. This may require the tuning of priorities or the special allocation of computer resources. It may require running different applications in virtual machines. You will want to make sure your OPC Server of choice supports your architecture.
Operating System Platforms – is supported on the operating systems important to you. In the world of industrial automation, the most common platform is Microsoft Windows. You will want to make sure your OPC Server runs on both workstation and server configurations and in scenarios with virtual machines. Linux is also becoming very popular and Docker equally so. Almost all OPC Servers support Microsoft operating systems, but more OPC Server vendors are delivering the Linux solution.
Price – is cost competitive with other available solutions. The price of OPC Server software varies greatly and is a major area of competition among vendors. It will be worth reviewing many of the market offerings, comparing technical abilities AND pricing, to make the right choice for your application.
License Model – offers license models that fit your OpEx/CapEx budget. Most vendors are enhancing license models. While perpetual license models with annual support programs were the norm just a few short years ago, models now include annual subscription support to fit OpEx (Operational Expense) rather than CapEx (Capital Expense) plus annual support pricing scenarios.
Ease of Use – is designed for user or programmatic configuration. The ease of configuration is also a major consideration for the selection of an OPC Server. Options for configuration include manual configuration through a set of menus and selections. Programmatic configuration through a set of APIs enables the support of external tools to automatically generate a configuration. Application configurations are often stored in easy-to-access file formats or databases. In many cases, tools for export and import are also available to support configuration and documentation in other software solutions, often Microsoft Excel.
Vendor Endorsed – provides solution endorsement by the protocol owner. The selection of an OPC Server becomes simple if the device vendor makes an OPC Server recommendation for you. They have vetted the solution and know of its operation along with their products. For example, Mitsubishi Electric and ICONICS have partnered with Takebishi and recommend the DeviceXPlorer OPC Server solution. Their products will also work with other OPC Server solutions, but Takebishi is in the unique position of being the OEM solution for both Mitsubishi Electric and ICONICS.
Certifications – meets protocol certification requirements. There are several seals of approval that should be considered when reviewing OPC Servers. The OPC Foundation offers a product certification process and database that lists all OPC Servers, both certified and not certified. There are also certifications for the various device protocols that are available. BACnet and BACnet/SC are protocols that are commonly certified as a seal of approval from the BTL (BACnet Testing Laboratory). CC-Link is tested through the CLPA (CC-Link Partner Association). Check if the managing authority of the protocol you are using offers a certification process and that the OPC Server of choice has met the certification requirements.
To end, selecting the right OPC Server is a crucial decision that can significantly impact the performance, reliability, and overall success of your control system. Factors to consider include performance, reliability, redundancy, technical support, northbound and southbound connectivity, flexibility, proven track record, distribution, compatibility, operating system support, pricing, licensing model, ease of use, vendor endorsement, and certifications. By carefully evaluating these criteria and considering the specific needs of your application, you can make an informed decision and choose the OPC Server that best meets your requirements.