1mS SOE

Process Plants have always had the challenge of diagnosing what happened after a plant shut down. Finding the root cause of a particular problem is difficult with perhaps 100’s or 1000 plant shutdown interlock contacts involved. Finding the fault and rectifying the fault as quickly as possible is of the essence as plant downtime is lost revenue. Finding these faults means tracking what is happening in the plant so that the conditions leading up to the trip can be reviewed and analysed. So every change of state needs to be captured i.e. Interlock contacts and trip or alarm statuses are continuously monitored. Sequence of Event Recorders deal with Events - An important concept to note is that although we are monitoring a relay contact which may be open or closed in it’s normal state when it changes state it becomes an event in the system implying that the time it changed state is captured as part of the history to be useful for post shut down diagnostics. The Sequence of Events recorder chronologically Time Stamps every change of state pinpointing its occurrence in time. Change of State (COS) = Open to Closed or vice versa Event = Open to Closed or vice versa and Time and Date Stamp The Benefit of a Sequence of Event Recorder The role of the Sequence of Event recorder is to compliment the supervisory and control system within the plant. Sequence of Event Recorder’s primary purpose is to assist in the diagnosis of root cause analysis of plant faults. Sequence of Event Recorder does this by chronologically logging all monitored changes of state of the inputs on a continuous basis. Eg 1milli-second vs 1second or more on supervisory systems. Record Pre and Post Event at 1msec resolution The SOE recorder captures changes of state on a continuous basis so the plant status can be reviewed before and after the trip event. By logging the events to a PC based Supervisory system database at the plant events can be stored over long periods of time. Resolve input changes of state to 1msec Current benchmark standard for Sequence of Event Recording is milli-second enabling a chain of events to be chronologically captured with enough resolution to discriminate between Changes of state down to a single milli-second apart. Analyse Downtime using Time Stamped at Source data. An essential component to accurate analysis of root cause leading to plant downtime. Event recorders need to time stamp a change of state at the source and as they happen so that a list of events can be reviewed and sorted into chronological order even on the other end of a slow communications network. This Time and Date Stamp cannot be added later without introducing errors due to communications latency. Referencing all events to a single time base An essential criteria of root cause is to analyse all events relative to the same time base and number of key features are required to ease the job of engineers analysing the system First Understand your Plant It is not enough to simply install a Sequence of Events recorder on a plant and expect the results to yield the route cause. An understanding of the plants operation and the resultant latency that process interlocks, alarms and trips have is essential. The SOE system will faithfully capture events down to millisecond resolution but cannot uncover primary latency in the system such as relay pick up or drop out time. This is a crucial phase in the implementation and configuration of the SOE system and essential to producing accurate results. Key Features of SOE recorders Input Sense detection Reading the status of inputs as open or closed is important in understanding the interlock arrangement and reviewing the status of the system. Adjustable Delay Timers One of the many issues in monitoring plant contacts is the disparity between pull in or drop out times on different types of relay. Individual delay Ti

For more information on 1mS SOE talk to Omniflex UK Limited