A Systematic Approach to Architecting Automated Test System Signal Switching Subsystems, from Design to Maintenance

Signal switching is a foundational building block of Automated Test Systems (ATS), often described as the heart of the system. Its primary role is to distribute and route stimulus and measurement signals between the Device Under Test (DUT) and test instrumentation I/O, thereby minimizing manual intervention, reducing test times, and decreasing the potential for human error. At its core, a switch operates as a binary function, connecting or disconnecting endpoints in a signal path. While this role may seem simplistic, the switch system is essentially an extension of the instrument or DUT I/O, and no system is ideal; even the best switch designs can impact signal fidelity.This paper discusses practical engineering principles that are often overlooked in designing signal switching systems, which can adversely affect test system reliability. Given that relays are at the core of switching subsystems and have a finite lifespan, the paper explores use cases that can degrade relay integrity and put system availability at risk. Particular attention is paid to best practices for extending the life of a switching system, including the effects of hot vs. cold switching on relay life and examples of predictive maintenance tools to maximize system uptime.