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The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) is the largest solar telescope in the world, utilizing a 4-m offset primary mirror that accumulates a 13-kW solar load. Safely offsetting and extracting that heat load is the Facility Management System (FMS), that controls all aspects of the Facility Thermal System (FTS). Using 3 PAC/PLC controllers, FMS provides coolant across 11 individual loops, each at different temperatures, to meet the requirements of the telescope, coude, enclosure, optics, and instruments, as well as controlling the Domestic Water System, the Energy Management System, Active and Passive ventilation, and the HVAC system including the Coudé Instrument Lab cleanroom. Control of all of these systems needs to be coordinated to provide the best thermal system performance based on the environmental conditions and operational requirements. Due to the unique and innovative nature of the observatory and the decision to self-perform a variety of construction work packages, all of the system programming and thermal instrumentation design was performed in-house. During DKIST’s construction phase, each subsystem was commissioned at the most basic acceptable level, then immediately put into a production environment due to pre-existing cooling demands of the facility. This led to a tight time budget to program and deliver the FMS, making sequential prototyping, commissioning, and acceptance nearly impossible. These parameters drove the need for a flexible programming approach, more similar to a retrofit than a new system-wide design, when performing system adjustments and integrating new subsystems. By using state machine programming, it is possible to design the system using diagrams that makes it easier to review potential system operations with all interested parties, including those that are not programmers. This also reduces the time to receive feedback from users, debugging time, and identifying edge cases all while making the logic more extensible and flexible. Presented herein is the programming methodology implemented in the FMS that allowed us to meet aggressive moving targets during construction, revise system operation and function in early operations commissioning, and ensures that the system will continue to provide necessary controls for the observatory while maintaining flexibility for future improvements.
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