Cost-effective solution for telescope control

DKIST enclosure
Image courtesy of IDOM, Spain.

Reduced costs and accelerated development are key benefits of using commercial-off-the-shelf software for telescope control.

The SPIE Astronomical Telescopes and Instrumentation conference was held in Amsterdam in July 2012. Alastair Borrowman of Observatory Sciences presented a paper discussing the benefits of using commercial-off-the-shelf (COTS) software for control of the Daniel K. Inouye Solar Telescope (DKIST) enclosure, which is under construction at Haleakala on the island of Maui, Hawaii.

As Programmable Logic Controllers (PLCs) evolve from simple logical controllers into more capable Programmable Automation Controllers (PACs), scientific facilities are making increasing use of such devices to control complex mechanisms. Observatory Sciences has incorporated COTS software into DKIST's Common Services Framework (CSF) software infrastructure to enable high-level control of hardware through a PAC. The paper presented at SPIE describes the Enclosure Control System (ECS) developed by OSL in the UK and by IDOM in Spain, detailing the selection and use of the PLCIO communication library from Commercial Timesharing Inc.

The library is implemented in C and delivered with source code. It separates the programmer from the controller's communication details through a simple Applications Programming Interface (API). Capable of communicating with many types of PACs/PLCs (including Allen-Bradley and Siemens) the API remains the same irrespective of the controller in use. The ECS is implemented in Java using the observatory's framework running on Linux. The link between Java and the PLCIO C library is provided by a thin Java Native Interface (JNI) layer.

To provide enhanced software testing capabilities prior to hardware becoming available, a software PAC simulator was developed based upon the PLCIO's Virtual PLC. This creates a simulator operating inside PLCIO and therefore below the level of the library's API. In this way the ECS uses the same software and operates in the same manner irrespective of whether it is connected to the real or simulated PAC, ensuring software used during testing is always the software used in operations.

Communication timing test data illustrates that the use of CSF, JNI and PLCIO provides a control system capable of controlling enclosure tracking mechanisms, and that would be equally valid for telescope mount control.

Read the full paper here »

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