PID Loops

Hello Guest,

Does keeping a list of all PID loops in a plant makes sense even if it is in a DCS? We use to keep a list of all PIDs on PLCs but is it any worth in maintaining a PID list in a DCS?

YES! You can never have too much information. You should not only have a list of every control loop, but the tuning parameters as well. All of these parameters will be in the software program for the system. Make SURE you have a backup copy of the program. I like to also have a printed copy of the program (usually ladder logic, but not necessarily these days) and all register values and assigned variables.

Also what can be consequences in long term if not maiantained one?

If you don't maintain a list, it will be more difficult to troubleshoot the system should problems arise. Maintaining a list allows you to review as time allows, which helps keep you cognizant of how the system works.

Mike

Ditto the above comment. Especially the tuning parameters and other current plant information. Generally people will keep copy of the programming, but the commissioning / operating data is generally lost (if for example the PLC dies).

I would suggest not just keeping a list of the PID loops, but the current operating parameters (PID tuning parameters, control and alarm setpoints). Backup of Historical operating data is also very useful.

Nothing is worse than getting a plant back up and going, then having to re-commission all the operating points.

Dear..DCS is quite large in terms of its capacity in storage/memory and other features like response ,redundancy at diffrenet levels. so ..in case you are maintaing a list in PLC in form of ladder logic or FBD, you must keep them in DCS as well. In fact the latest DCS are windows XP based and it is very easy to have a desired data of all loops,logics,their various settings, PID values, alarm sets etc..Also you should have all the related links and interlocks listed against all open and close loops. Thiswill help you finding quick reference in case of troubleshooting,diagnosis, etc.. Not to mention if you can have a back of all data related to your process control including PID loops, interlocks.graphics, history in a separted CD or external hard disk, or in partition of running hard disk. Keep all these updated as well periodically to updtae any run-time changes and any addition/deletion of tags/loops, tuning values etc. This is very important. A hard copy is also essential as a safe back up in case of GOD-forbid any emergency or breakdown related to hardware/software or a natural calamity etc and if you are to start from a scratch to rebuild your data base. In a continuous process plant where process control automation holds the key all this has to be taken care indispensably.. Best wishes..M S Vilkhoo AGM(Inst) Siel Chemical Complex: Rajpura(Punjab)INDIA