PLC SIL rating

[Dave46 0]

hi all can anyone recommend brand of PLCs that have SIL 2 rating , (safety integrity level) thanks

[Big Country 3]

You may look at STI they carry a model of safety controllers I beleive it a CQM series.

[paulengr 44]

Allen Bradley has an entire technical document for the ControlLogix processors detailing how to make them SIL 2 compliant. In addition, they also have several other "safety PLC" series that do the job. At least with their PLC's, you work in a special subset of the full ladder logic when doing safety PLC ladders. Frankly, I've found little use for it. I can easily implement up to SIL 4 using discrete logic safety relays even with some fairly tricky interlock schemes. Other than diagnostics (which you can get with safety relays too), and the ability to use a network protocol (there are safety relays that support DeviceNet directly, too), I haven't found any use for the extra expense of a safety PLC. That being said, Chrysler automatically installs "safety" grade ControlLogix PLC's on most of their assembly lines.

[Mike Dyble 0]

Also its not just the PLC that has to be SIL2, all the associated engineering and sensors also have to meet SIL2 requirements. Siemens also do a range of systems. I have to agree with Paulengr Safety PLC's are best avoided, one of the things that a safety circuit/system should ideally be is simple, that way there is less room for error in the future. By all means monitor status for display on HMI's (Theres nothing worse than a long ESTOP chain and not knowing which one has operated), but try and keep safety control separate and simple. Edited 10 Jul 2008 by Mike Dyble