Dynamic Exception Handling Based on Web Services and OPC XML-DA

Programmable Logic Controllers (PLC) are widely used in process automation due to their fast and guarantee response time. However their programming and interfacing capacities are limited. In this paper we present a Surveillance software aimed to extend the range of actions available to deal with anomalous situations that are not critical in terms of time and to complement any actions implemented by other units in critical situations. The system combines the possibilities offered by standard OPC XML-DA, the integration capabilities provided by web services and rule-based engines with state-of-the-art technologies for communication such as e-mail, SMS, instant messaging or VoIP. Variables values are monitored by the component using OPC XML-DA and a set of previously defined rules that can trigger actions via web service invocations. These two characteristics allow creating a dynamic behaviour able to handle exceptions. In summary, this component extends control capacities and facilitates exception processing on PLC and NC.