Doubt Regarding DCS/PLC

maya3369 said:

Dcs is distributed control system.
Plc is Programable logic controler.

Dcs is used to control the process parameters like pressure, flow, temperature etc...
Plc is used to compute, control , monitor the process safety logics, start up and shut down activities in a laymens language.

now Plc is not distributed and it is not in that category.

What is distribution? simplly know first the difference between centralised and distributed.
centralised only one person can control, destributed many people can control.
now u go back to the conventional controlling and monitoring of instrumentation.

In the past the panel/mimic mounted individual controllers to control the parameters. one for temp and one for level etc on a vertical panel many many...with only one operator standing and monitoring each unit at a time for one single unit. one panel for steam boilers control panel. one panel and operator for turbine control panel etc...
so one operator can view and monitor only one panel that too one controller...

here in dcs one monitor or console /operator can have/view more than 10000 tags and at a time can view many controllers and can view and control other units also. so controlling is distributed from any console any operator can view or control the parameters of any unit. depends on configuration. this is called controll distribution. distributed control system " minitoring and controlling can be from any where to any where" bluntly

plc also can be manipulated in this manner u can have no of plc mmi's to do the same as DCS. but since it is not a regulatory control like dcs "it dont need every time controlling" the term distributed logic controller. it is once for all programed logic controller. so plc as it is equavalent to DCS electronically it is not used as distributed and hence it can not be in the cat'ry.

mvr.

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plchacker said:

There are several ways to use multiple PLC Processors to control multiple processes, and have multiple HMI's for inputs. One basic way is to have individual processors/PLCs control small processes, and link them with some network so that they all work together. I have seen this done for speeds sake, on fast assembly machines.

Another way, is with redundant controllers. Think of two or more processors running the same program attached to the same I/O. In this case, if one processor fails, then another keeps the machine running without a noticeable change. DCS uses redundancy. CLX can be configured for redundancy too.



I have distributed multiple copies of a single HMI project throughout the mill. In those cases, I limited which stations had the right to make changes, but all could monitor the system.



DCS systems were developed for processes that have lots of instrumentation loops. PLC's were developed for lots of discreet I/O. Over the years both have reached toward a middle ground. Still, both have their place in the world. I'd hardly want to control a high speed lumber sorter/stacker with a DCS. Likewise, I'd run for the hills if someone told me that I needed to control the back side of a paper mill with PLC's. (pulping process)



I know, incoming. :0

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maya3369 said:

yes we can use many plc MMI's to monitor logics start up and shut down like in DCS if the set up is asking for.

in normal plants once we program plc we dont need to monitor plc continuosly like DCs. unless there is a problem. Plc is a fixed depoiste u will touch in emmergeny situations. dcs is like current account which u need to operate always... so no body spend multiple plc interfaces for fun. the plc iterface is only to the maintainence person not for the operator.

so the plc is not coming in the category of distibuted...but alwasy you can make function the plc as dcs...plc is capable of doing the job plc does up to some extent. dcs is capable of doing the job of plc job up to some extent. there is a flexibility up to some extent.

it is like donkey and horse. both can run and carry the loads...but donkey carry lot and horse run fast...

now it is ur turn to compare dcs plc with other two...

mvr.

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