Would like to know how to determine whether a signal should go to DCS/PLC or ESD (Emergency Shutdown Device)?

I'm looking at transmitter with alarm & indicator, I notice for that for transmitters with alarm High/Low, all signal goes to DCS while when alarm has HighHigh/LowLow, the Transmitter & Alarm signal will go to ESD, while Indicator remains connected to DCS. I assume for serious alarms they go to ESD while normal alarm goes to DCS.

But what about other instruments like Shutdown Valves, Relief Valves etc? I notice solenoid valves for a Shutdown Valve goes to ESD while the limit switch, position indicators goes to DCS.

 

Wow are you venturing into new and uncharted territory (for you) from the sounds of it.

What you are seeing are the outward signs and conventions used to represent the results of a complex decision making process for large plant. I guessed your area from the terms you use so I may be out here.

The terms to search for on the www for current recognised best practice are

- functional safety
- IEC 61508

These are modern risk based methods of making the decision. Be prepared for a lot of reading, a lot of chats with other disciplines, a lot of, sometimes ill-informed advice, and probably some arguments.

If you are looking at an older system look for docs like API RP14C which adopted a more prescriptive approach to particular items of plant. Other industries and countries did have similar guidance I believe e.g. nuclear, large fired plant (NFPA?). Company and country standards for your industry sector if they exist would be another good source.

I wish you the best.
DaveMH

 

The design philosophy (IPF) depends on your company requirements and regulations.
In general none critical measurements which are classified as alarm only (f.i heater ON/OFF or trip signal) will be connected in the DCS. Other critical signals such as, process protection and Fire&Gas protection will be connected to the ESD which will actuate the final element (close block valve, open flare valve etc.)in case of an emergency such as fire alarm.

Good Luck...

 

Dear sir
Whenever the devices which main source regulator for running the process and shutting down them will result in process output to zero, those field devices/drives will be connected to ESD. Such as Trip valves of burner, Mill Pneumatic quick seal valve (PQSV)and etc., which are very much Pillar for the process. When some process dynamics goes out of range the same is to shutoff quickly. So whenever designing a process control this has to be taken care. So most of control system in Plants goes with these types of shutoff devices in a separate PLC in TMR configuration as ESD control.