Speaker
Description
At scientific neutron source facilities, instrument shutter systems are the primary mechanism for beam control at an instrument. Given the criticality of these systems, they must be engineered for safety for hazard control, high reliability to minimize scientific downtime, and maintainability across a large fleet of instruments. This presentation details the best practices developed at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) for the integrated design of instrument shutter control systems.
On the hardware front, the discussion examines the selection of Programmable Logic Controllers (PLCs) versus custom circuitry, the importance of placement of system components, and the implementation of fail-safe wiring, such as the use of normally closed (NC) circuits for interlocks to ensure positive state determination. Special emphasis is placed on indicate-safe signage, ensuring that a single electrical failure cannot falsely indicate a safe condition.
From a software perspective, the work outlines standardized PLC programming patterns designed to eliminate common failure modes. This includes techniques from latch/unlatch logic to state machines and step-complete architectures. Input and output (IO) mapping and abstraction are suggested as well as heavy use of internal variables.
Furthermore, the human-machine controls are addressed, focusing on the ergonomics of control placement and the psychological impact of signage and alarms. The work advocates for consideration of color associations, text pairing, and accessibility.
Finally, this work presents lessons learned based on failure modes encountered at the NCNR. By synthesizing these experiences into a set of design standards, this presentation provides a roadmap for developing instrument shutter control systems that are safe, reliable, and maintainable to minimize human and system error.
Key Words
Shutter, Control, Electronics, Hardware, Software, Safety, Reliability, Maintainability, PLC