Suitability Assessment of Opc Ua as the Backbone of Ground-based Observatory Control Systems

A common requirement of modern observatory control systems is to allow interaction between various heterogeneous subsystems in a transparent way. However, the integration of off-the-shelf (OTS) industrial products such as Programmable Logic Controllers (PLCs) and Supervisory Control And Data Acquisition (SCADA) software has long been hampered by the lack of an adequate interfacing method. With the advent of the Unified Architecture (UA) version of OPC (Object Linking and Embedding for Process Control), the limitations of the original industryaccepted interface are now lifted, and also much more functionality has been defined. In this paper the most important features of OPC UA are matched against the requirements of ground-based observatory control systems in general and in particular of the 1.2m Mercator Telescope. We investigate the opportunities of the “information modelling” idea behind OPC UA, which could allow an extensive standardization in the field of astronomical instrumentation, similar to the efforts emerging in several industry domains. Because OPC UA is designed for both horizontal and vertical integration of heterogeneous subsystems, we explore its capabilities to serve as the backbone of a dependable and scalable observatory control system, treating industrial components like PLCs no differently than custom software components. Performance measurements and tests with a sample of OTS OPC UA products are presented.