Thanks to Emerson’s Mike Boudreaux and Kim Conner for writing this post while I’m on vacation this week.
Emerson’s David Sheppard presented A straightforward approach using DeltaV SIS for typical BMS systems at Emerson Exchange. David is a certified functional safety expert (CFSE) and he has worked on many safety system projects as an SIS Lead Project Engineer.
David presented general considerations for burner management systems and then provided some details on how to implement burner management system (BMS) applications with DeltaV SIS, based on his own personal experience on Emerson projects. One of the key points that he discussed was the importance of reducing the complexity of a BMS application.
DeltaV SIS provides advanced function blocks that simplify configuration. Three of the IEC 61508-certified function blocks in DeltaV SIS are specifically designed for the sequential nature of BMS applications. These are the State Transition, Step Sequencer, and Cause and Effect function blocks.
David said that a big difference with using the State Transition function block compared with ladder logic is how clearly the logic is defined. This clear definition of logic is important to two main groups who need the data-engineers and operators.
First, the engineers have to compile, transmit and convey the data to the programmers, factory acceptance test (FAT) team, etc. Some approaches use narrative write-ups to share the logic and sequencing. Depending on how good the write-up is, a narrative may leave out some key items and leave people to make assumptions.
However, David says with the DeltaV SIS State Transition function block, “On one page, we can show the states, the trip conditions that should be active, what position every valve is in each state, and how to move from state to state.” There is no question on the design; it is locked down and clear. For example, everyone can easily see that valve XY-101 should be ‘open’ in states 6-10.
Secondly, the information needs to be conveyed to the operators. Some burner management systems run for months at a time and are only started up once or twice a year. In these cases, an operator may not be very familiar with the logic. It is important to clearly display the sequencing steps and any interlocks so that the operators can quickly assess a situation, even when that situation is unfamiliar. A combination of both function blocks and operator graphics capabilities makes BMS information easy to identify with DeltaV SIS. First out traps, interlocks and sequencing steps enable operators to act quickly.
Reducing complexity for engineers and operators can increase the safety integrity of a BMS because the data is easy to understand and act upon. Availability and standards compliance should also be considered when implementing a burner management system, which we’ll address in later posts.