Smart instruments in safety instrumented systems - Sellafield experiences

Sellafield defines a Smart Instrument as one that meets the requirement to measure a single process variable. It includes flexibility in its use due to parameters set by the Manufacturer or User. Smart Instrument can also communicate by using the Highway Address Remote Transmitter (HART) language. This is based on the Bell 212 protocol operating at 300 baud. The difficulty of substantiation of the reliability of the firmware is one of the main concern of using Smart Instruments in safety Instrumented Systems. The commercial availability and inherent ability to diagnose failure are the primary reasons for these instruments as an emerging trend in non-nuclear safety instrumented systems. The ability of Smart Instruments to measure complex parameters is another important reason. The actual reliability of instruments used at Sellafield, both Smart and dumb, have been catalogued in the SRdB. Sellafield also has several other Smart Instruments in non-safety and safety instrumented systems on the Sellafield site.