Combining mechanical interlocks with safety sensors

10 February 2015

While interlocks ensure extremely high safety levels, they usually function as stand-alone safety systems. New digital technologies are now emerging that enable traditional interlocking to be combined with digital process control and instrumentation systems. Smith Flow Control is the first company to combine these mutually beneficial technologies in the development of the SmartTrap+, which incorporates signals from sensors into the interlocking sequence.

Mechanical interlocking guarantees that all required valve operations are performed, but cannot guarantee the outcomes of these operations. For example, opening and closing a vent valve does not give real time information that the vessel pressure has actually reached a safe level; while opening and closing a drain valve does not guarantee that all residues have been removed. By incorporating signals from other field devices like pressure or H2S/CO2 sensors into the interlocking sequence, the SmartTrap+ ensures interlock keys can only be released if particular process conditions have been met. SmartTrap+ incorporates permissive signals and a door lock proximity switch (4-20mA) as standard. The signals can include (but are not limited to) pressure detection, gas detection, flow/ level and pig detection.

By incorporating the best of traditional mechanical interlocking with process sensor information to ensure all vessels are safe to access, SmartTrap+ can help to reduce accidents and reduce downtime.