A sequence of events recorder (SER)[1] is an intelligent standalone microprocessor based system, which monitors external inputs and records the time and sequence of the changes.
SERs enable rapid root cause analysis after multiple events have occurred due to the secure recording of the sequence of events in the order of occurrence.
SERs are therefore utilized as a diagnostic tool to minimize plant downtime.
In 1984, the Tetragenics Company, a subsidiary of the Montana Power Company, introduced the first remote terminal unit (RTU) that time-tagged events to the nearest millisecond, and now there are also other RTUs with this capability.
Digital protective relays and some PLCs now also include time-tagging to the nearest millisecond; SCADA systems that incorporate these devices provide SER functions without a dedicated SER device.