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I am looking for system having DCS as main controller and SIL-3 PLC for critical operations. I want to generate some of the process interlocks from DCS and want to convey it to PLC. PLC status should also be communicated back to DCS. Please suggest any product of such sort having high speed communication and also remote I/O for far off plants (500 m)

Be very careful with this, it really depends on what kind of interlocks you are talking about. If you want to ensure that you maintain your SIL rating in the PLC it would be advisable to hardwire your interlocks. By using the DCS as the source of the interlock you are reducing the reliability of that interlock. You could hardwire the interlocks, or use a comms bus like Modbus or Profibus, but the specifics will depend on the capabilities of both your DCS and the PLC and the required reliability level of that interlock. You need to engineer these on a case by case basis.

Status information back to the DCS would be relatively easy, you could use a Profibus link or similar. If you are only indicating to the HMI you could use OPC. Once again this depends on the particular systems you have.

Chris Jennings

Thanks Chris for your reply. I have one more question, will making controllers of individual plant sections independent to each other will make my system more reliable (so as to avoid peer to peer communication)?

YES