A technical white paper exploring the possibilities available to designers of safety instrumented systems (SIS) using logic solvers as part of a tank-overfill protection system was released by Moore Industries-International Inc., North Hills, Calif.
“Logic Solver for Tank Overfill Protection” provides examples of straightforward tank-overfill protection system topographies and associated safety integrity level (SIL) calculations.
A tank-overfill protection system is an SIS that provides automated overfill control during the containment of dangerous substances. If the level in a tank rises above set limits, the logic solver initiates the final element of the SIS to make the process safe. This can include shutting off the input feed to the tank by isolating the pump and closing the input valve.
The white paper guides safety engineers through the steps needed to determine the right logic solver for their needs. While many people assume that a logic solver for a tank-overfill protection system must be a safety PLC, in many cases, a discrete logic device in the safety loop is sufficient. This avoids the complications associated with a complex programmable solution.
The white paper shows the methodology and calculations for determining applicable logic solvers in SIL 1 and SIL 2 environments. In many cases, discrete logic devices such as a safety trip alarm are suitable.
The white paper is available for download at http://bit.ly/1d0KR46.