Getting more from OPC A&E white paper

Getting More from OPC A&E

Easily access OPC A&E from multiple network sources, or convert it to OPC DA, UA and other protocols using DataHub middleware.

OPC Alarms and Events (OPC A&E) is a data communications protocol for conveying information about process alarms and events. A&E data can be used to notify operators and management of system problems and convey sequences of events to optimize operations. Such information is invaluable for scheduling maintenance and predicting equipment failure. However, A&E data is often hidden away on the plant floor, in multiple locations, making it hard to access from an IT department or central office where it could provide valuable insights for corporate management.

To get the most out of OPC A&E, you need secure, convenient and reliable access to the data. This is more challenging than you might think, because unlike OPC DA, there are not many tools available for networking or integrating OPC A&E.  DataHub middleware stands out as one of the few widely-used and field-tested OPC A&E integration solutions, offering networking, aggregation, redundancy, and conversion of the OPC A&E protocol itself.

For example, the recently-completed 1850-kilometer Trans-Anatolian Natural Gas Pipeline (TANAP) in Turkey uses DataHub middleware to support highly redundant, secure communications of OPC A&E data.  This case study describes how every aspect of operation is successfully coordinated between remote stations and central control.


OPC A&E is a COM-based technology, developed in the 1990s, that relies on DCOM (Distributed COM) for networking. Although it is now widely used, DCOM was never designed for real-time industrial applications. It is not as robust or secure as these mission-critical systems increasingly require, and it is notoriously difficult to configure. To make matters worse, there are very few diagnostic tools available for debugging A&E DCOM problems, so trouble-shooting becomes an arduous task.  Because of these problems, OPC A&E is often the weak link when trying to secure an industrial control system.

Getting More from OPC A&E diagram 1

To overcome these limitations, DataHub middleware offers A&E tunnelling to connect OPC A&E clients and servers over a network, avoiding DCOM altogether. This uses the same proven DHTP technology that the DataHub program uses for tunnelling OPC DA and OPC UA. DataHub tunnelling is unique in that it never blocks OPC or drops the local OPC connection. It detects network breaks in seconds, and recovers from them smoothly, without breaking the OPC A&E server or client connection.

The secure-by-design DataHub architecture allows it to make outbound connections from behind plant firewalls, keeping all inbound firewall ports closed. It supports seamless connectivity through proxy servers and DMZs, giving it high marks from IT departments responsible for corporate network security.

The DataHub modular design means that the OPC A&E tunneling can be integrated with other DataHub features, supporting aggregation of A&E servers, redundant A&E tunnels, and A&E data conversions to OPC DA and UA.

Protocol Conversion

The value of alarm and event data generated by OPC A&E servers often goes beyond the immediate context of an A&E client.  Many people find it useful to expose this A&E information to systems that don’t support the A&E protocol at all, such as reporting packages and SCADA systems. Others might need to convert it to OPC UA Alarms and Conditions (A&C) data.

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Again, the unique DataHub architecture plays an important role here, enabling protocol conversion. Internally, all of the data points in a DataHub instance are maintained as a single, unified data set.  Whenever it receives a change to a data point value, it immediately updates the data set, and then forwards the new value to every application subscribed to that point, in that application’s own protocol. In this way, incoming OPC A&E data can be passed to OPC UA or DA clients. This architecture also provides the ability to write A&E data to SQL databases, Excel spreadsheets, custom programs, and more.


Seeing the big picture and locating the weak points and potential trouble spots in a system often requires pulling together alarm and event data from multiple sources. As systems grow in complexity, and as demand grows for more remote monitoring of alarms and events, it can help to simplify incoming OPC A&E data streams by consolidating them. Aggregating A&E data also helps reduce network traffic and free up bandwidth on busy systems.

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A DataHub instance connects to any number of OPC A&E servers, and collects their current alarm and event data. All of this data can then be accessed by one or more local A&E clients, or tunnelled across the network to any number of remote A&E clients. Whenever any client acknowledges an alarm, the server retransmits that to all connected clients. In this way, you can have multiple OPC A&E servers communicating bidirectionally with multiple A&E clients.


System integrators and plant engineers often use redundant data paths to ensure the effectiveness of OPC A&E. After all, if an alarm message doesn’t reach its destination, it’s useless. Since networks are never 100% reliable, adding redundancy for A&E connections significantly improves the chances of alarms being received and acted upon.

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Implementing OPC A&E redundancy typically means configuring two OPC A&E servers to connect to the same data source and then tunnelling the data from each A&E server to a redundancy broker on the client side.  The redundancy broker monitors both tunnel connections and sends the data to the OPC A&E client (or clients).  Should one of the connections fail, the redundancy broker immediately switches over to the other tunnel connection and the client continues to operate with the current data.

The DataHub Redundancy feature lets it act as a redundancy broker. It channels the incoming data from the two tunnels into two identical input data domains.  One of those domains is used to feed a third (output) domain for the client. Switchover logic configured in the DataHub instance determines how and when a data stream is considered invalid, and triggers a switchover to the second, identical data stream. This switchover happens in a matter of milliseconds, which allows the client to continue uninterrupted.

Data Logging

The DataHub program is often used for logging OPC A&E data.  It is possible to maintain a permanent record of events in  a database, and access that data with your favorite reporting tool.

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Rather than simply logging an event as a single block of text, a DataHub instance can manipulate the messages.  It can be configured to extract the data from a single A&E message by assigning each A&E status variable to a separate data point. Each of these data points can then be sent via the ODBC protocol to an SQL database, for easy access by analysts and others on the IT team.

With the advent of Industrie 4.0 and the Industrial IoT, plant engineers and managers are receiving more and more requests from management for production data of all kinds. Having proven its worth for on-site, day-to-day operations, OPC A&E is now attracting attention from analysts and upper management who envision applying it in broader, large-scale planning and efficiency initiatives. DataHub middleware can play an important role in turning this vision into reality. All over the world companies are using DataHub software to aggregate OPC A&E data, send it across redundant networks, and convert it to OPC DA, UA, and other protocols.  Maybe yours will be next.