Posted 8 Jul 2008 hi all can anyone recommend brand of PLCs that have SIL 2 rating , (safety integrity level) thanks Share this post Link to post Share on other sites
Posted 10 Jul 2008 You may look at STI they carry a model of safety controllers I beleive it a CQM series. Share this post Link to post Share on other sites
Posted 10 Jul 2008 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. Share this post Link to post Share on other sites
Posted 10 Jul 2008 (edited) 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 Share this post Link to post Share on other sites