Difference between Cause & effect and Control Narratives

[vikkoo7]

Dears,

From my past experience i have been noticed that Cause & effect diagrams are used for ESD systems and Control Narratives are using for DCS..

can anybody confirm this,that my understanding is correct...

Also specify Cause & effect is available for DCS also..

What are the standard practices

[thewall]

Control Narratives is the document explaining the control system of the plant (or of a portion on the plant).
C&E Table/Diagrams explain the the safety interlocks of the same plant.
Normally the C&E Table is implemented in the ESD (if any) otherwise it can be implemented in the DCS (for example if SIL analisys is not required because the plant is not dangerous).

Pratical example:

Consider a vessel refilled with a fluid through a level control valves.
The control narratives will explain the functioning of this control loop (Level Transmitter - Level controller - Level control valve).

Consider on the same vessel another level transmitter and a shutoff valve on the refill line to protect the vessel from overfilling.
The C&E table will explain safety loop (level transmitter - HH level interlock - shutoff valve)

[mrkssastry]

A good start for the explanation. I just want to add the following.

1. Control Narrative: It is a document which explains the functioning of DCS system - control loops, open loops, duty / standby pump operations, duty, standby, assist operations, etc. For a control loop, the control narrative document explains the type of control (PID / PI / P / ratio control / cascade control / feedforward control etc), control set point, controller action, output direction, modes of operation of the controller (manual mode, auto mode, cascade mode etc), PV tracking options, output type in case of controller failure (output goes to 100% / 0%, stay put / stay safe) etc.


For a duty standby pump operation the control narrative explains the concept of auto changeover in detail - wht happens when there is a trip of first pump, what should happen to the system when the cmmand goes to pump for start but it does not start etc. It also explains under what circumstances auto changeover is achieved and under what circumstances, operator intervention is required.

2. Cause & Effect chart: The name itself is very clear. It clearly is a document which explains if a cause happens what should be the effect. Typically C&E charts are prepared for ESD, F&G, all the individual package systems where PLC systems are involved in implementing interlocks. DCS system is not an exception to this. Even DCS system can have its own C&E even though there is a separate ESD system to take care of the shutdown.

Hope i am clear. Please do not hesitate to ask more in case of clarification.

[josefreitas]

In my project we need to do a SIL study. The Client specify SIL 3 for Control. You can help me with a SIL report in order to check the process phases that i need to analyse. I appreciate if can send to me one report jose_manuel_freitas@yahoo.com

[ravivva]

thanks

[Season Engg]

Thanks

[Jibeesh]

hai jr...google "kishore karuppaswamy" for instrumentation text books for free