Difference between DCS & PLC Systems

DCS’s were designed to control processes, not discrete operations. As such, a large number of the inputs and outputs are analog like a 4-20mA signal or 0-10V signal.

DCS stands for “Distributed Control System”

In Literary meaning, a Distributed Control System (DCS) refers to a control system usually of a process or manufacturing system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or more controllers.  Process plants used to have long series of panel mounted Single Loop Controllers (Analog/PID controllers).

 PLC stands for “Programmable Logic Controller”

Historically a PLC was in discrete control of manufacturing processes. Whole discrete logic used to be implemented with relay circuitry. Most of the inputs and outputs for discrete control are binary, meaning they have only two states: On and Off.

What are attributes and characteristics which differentiate the PLC system from the DCS. There have been claims and counter claims from different manufacturers that their system is DCS or PLC.

The topic has remained under debate for long, and especially today when we have already entered into new era of Hybrid Distributed Control Systems, it has become increasingly difficult to select and differentiate the advantages and drawbacks one can get from different systems.

 There are few similarities and dissimilarities which  I would like to mention here:

1) DCS are designed or made available to the user in a way that only configuration in form of a Functional Block has to be carried out unlike PLC, where complete programming has to be implemented using any one of the different languages available in the system. Now, Functional Blocks are also available in the PLC systems, which really makes it comparable to DCS.

2) When DCS started emerging in the market, idea was to supply DCS with whole bunch of hardware and software packages including for Human Interface, necessary for the complete automation of the plant, thus facilitating Single Point Configuration in terms of database and communication possible in  general.

Additionally, Human Interface does not need separate communication package i.e DDE server, to communicate with the controller. DCS includes higher levels of application software for regulatory and batch control.

 In case of PLC systems, PLC were not suppose to be in packages but competition with DCS vendors forced the PLC manufacturers to offer necessary all other softwares and packages.

3) Many DCS are designed such that it is possible to configure cycle time for each Functional Block. Thus DCS system takes care of cycle time scheduling of the Functional Blocks which are the basic execution units.

This is one of the reason that overall scan time of the DCS is comparatively higher than the PLC system.This functionality has been introduced in PLC systems(s) in some form as well.

4) A DCS has inherently multiple processor capability thus making the functionality distributed across a network.

In a typical multi-processors (multi-node) DCS architecture, Engineer has to put in less efforts for inter-communication of the processors or one controller can easily access the Tag(s) from the database of the other .i.e the input of FB in one controller can be output of FB of the other controller. This is possible now in PLC but more efforts have to be put in.

5) DCS programming is centered around configuration of Functional Blocks and discrete logic is implemented in DCS using FBs, thus making the DCS inherently an analog control system (although ladder programming is also possible in some of the DCS also).

PLCs were programmed using Ladder/Relay language , before arrival of IEC 1131-3 standard and Analog control was incorporated inside Ladder inside Ladder Logic using special FBs. This is probably the reason we look at some of the process plants that process  (Analog) control is done by the DCS, while emergency control (Discrete Control) is implemented by PLC based systems.

6) PLCs are still being used at RTU stations because of their simple, small and cheaper architecture as well as engineering (typically the RTU application) instead of big DCS.

DCS have been used as the central system in a SCADA network. In a typical SCADA scenario, one DCS is connected to many PLCs systems.

7) Being Discrete in nature, PLC was natural choice of manufacturer and end-user to apply it for safety system. This led to production of specialized safety system conforming to SIL3 certification in accordance with ANSI / ISA 84.00.01-2004.

Today,  a lot has changed, it is difficult to distinguish between two systems in terms of its main features. Differences between the two has virtually vanished due to Programming / Configuration language standard IEC-61131.

The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking.

However, in major industrial areas and structure markets, it is practice to deploy DCS for process control and PLC based system for safety control.

Perhaps, for a large install base like more than 1000 I/Os system, cost of installation, addition and maintenance per I/O is less in case of DCS system.

Now, more important is cost, application, system integrity, reliability, maintainability, historical logging / intelligent statistics and learning / training. How much support is available from the vendor for the operation matters most to the operator now.

This has resulted into ‘Solutions Packages’ by vendors to their customers instead of simply offering individual products. It is DCS or PLC, must come in a solution package.

More and improved System functionalities have made these system more complex which require strong integration between the operator /user  and the manufacturer.

This article was originally posted on Instrumentation Tools and I am posting it with due courtesy.

Potatoes, Eggs, and Coffee Beans

Once upon a time a daughter complained to her father that her life was miserable and that she didn’t know how she was going to make it. She was tired of fighting and struggling all the time. It seemed just as one problem was solved, another one soon followed.

Her father, a chef, took her to the kitchen. He filled three pots with water and placed each on a high fire. Once the three pots began to boil, he placed potatoes in one pot, eggs in the second pot, and ground coffee beans in the third pot.

He then let them sit and boil, without saying a word to his daughter. The daughter, moaned and impatiently waited, wondering what he was doing.

After twenty minutes he turned off the burners. He took the potatoes out of the pot and placed them in a bowl. He pulled the boiled eggs out and placed them in a bowl.

He then ladled the coffee out and placed it in a cup. Turning to her he asked. “Daughter, what do you see?”

“Potatoes, eggs, and coffee,” she hastily replied.

“Look closer,” he said, “and touch the potatoes.” She did and noted that they were soft. He then asked her to take an egg and break it. After pulling off the shell, she observed the hard-boiled egg. Finally, he asked her to sip the coffee. Its rich aroma brought a smile to her face.

“Father, what does this mean?” she asked

He then explained that the potatoes, the eggs and coffee beans had each faced the same adversity– the boiling water.

However, each one reacted differently.

The potato went in strong, hard, and unrelenting, but in boiling water, it became soft and weak.

The egg was fragile, with the thin outer shell protecting its liquid interior until it was put in the boiling water. Then the inside of the egg became hard.

However, the ground coffee beans were unique. After they were exposed to the boiling water, they changed the water and created something new.

“Which are you,” he asked his daughter. “When adversity knocks on your door, how do you respond? Are you a potato, an egg, or a coffee bean? “

Moral:In life, things happen around us, things happen to us, but the only thing that truly matters is what happens within us.

Which one are you?

Originally posted on Livin3

The Daily Doze

 Shake off Your Problems

A man’s favorite donkey falls into a deep precipice. He can’t pull it out no matter how hard he tries. He therefore decides to bury it alive.

Soil is poured onto the donkey from above. The donkey feels the load, shakes it off, and steps on it. More soil is poured.

It shakes it off and steps up. The more the load was poured, the higher it rose. By noon, the donkey was grazing in green pastures.

After much shaking off (of problems) And stepping up (learning from them), One will graze in GREEN PASTURES.

Life is memories in bits and pieces.

This is a very warm sunny day of later summer season. The trees were colored with green and some yellow leaves. He was sitting underneath an old tree with his back to the trunk. He closed his eyes and let himself dwell into the memories of the past.

He was thinking every thing git slipped so fast from his fist but yet there were these small parts which had a whole world in them. He had smiled, he had wept. He had shared. he had help and got help. There were many people who had laughed and smiled because of him. There were kids who had stopped crying because of his small generosity. There were people who had got there needs fulfilled without being asked as he had noticed and helped.

There was he many a times struggling with life but yet there were moments he had enjoyed, those small moments which he never noticed and never realized how important and beautiful.

Watching these flash backs he realized that life has not been as unfair as he was thinking. He had though may be small but there were moments of joy, of success and of smiling.

Suddenly there was this wind blow and dust blow from the front and hit him on face and he returned to his present moment. he looked around. The wind was blowing. Many birds were flying in flocks and there were other animals grazing here and there. The water was flowing besides him with a sweet sound. He these flash back has yet again helped him avoid a life collapse and this was perhaps one of many such. No matter how hard life is those small moments of his being good and honest to himself and others will keep him floating.

The world surrounding him was falling apart. He couldn’t do nay thing but to see it fly into the air like sand. This was not a momentary event. He has been struggling with his own self for years. He made many promises to himself and broke them. The most difficult part for him was being honest to himself. He always lived a reflected life.

He got up and star walking and he was thinking how life would be if he over come his short comings and fulfilled his promises to himself and live as true himself every moment. This hope keeps him moving ahead.

Life goes on

The Obstacle in our Path

There once was a very wealthy and curious king. This king had a huge boulder placed in the middle of a road. Then he hid nearby to see if anyone would try to remove the gigantic rock from the road.

The first people to pass by were some of the king’s wealthiest merchants and courtiers. Rather than moving it, they simply walked around it. A few loudly blamed the King for not maintaining the roads. Not one of them tried to move the boulder.

Finally, a peasant came along. His arms were full of vegetables. When he got near the boulder, rather than simply walking around it as the others had, the peasant put down his load and tried to move the stone to the side of the road. It took a lot of effort but he finally succeeded.

The peasant gathered up his load and was ready to go on his way when he say a purse lying in the road where the boulder had been. The peasant opened the purse. The purse was stuffed full of gold coins and a note from the king. The king’s note said the purse’s gold was a reward for moving the boulder from the road.

The king showed the peasant what many of us never understand: every obstacle presents an opportunity to improve our condition.

Courtesy: livin3

Some Bits of Inspiration

1. Everyone Has a Story in Life

A 24 year old boy seeing out from the train’s window shouted…

“Dad, look the trees are going behind!”

Dad smiled and a young couple sitting nearby, looked at the 24 year old’s childish behavior with pity, suddenly he again exclaimed…

“Dad, look the clouds are running with us!

The couple couldn’t resist and said to the old man…

“Why don’t you take your son to a good doctor?” The old man smiled and said…“I did and we are just coming from the hospital, my son was blind from birth, he just got his eyes today.”

Every single person on the planet has a story. Don’t judge people before you truly know them. The truth might surprise you


A Trip to Kashmir

one day one of my good friend, Fida Ali, called me and asked me if I want to join them for a trip to Kashmir. I said I will think  and then considering it as usual talk to be forgotten, I didnt respond. After two days he called again and ask what was my decision. I declined but he insisted and yet again I got time to think over it and then I made quite a few excuse to respond on his next call. As usual my excuses were of no use as he had made up his mind and I was already  part of the trip. So it was decided and I agreed to join them in Abbotabad that early morning.

I do not like the trips till the time i get out of the room so I was excited already when I left from Lahore. It was 10pm and I started my journey from Lahore. I reached Abbotabad early morning and had a delicious breakfast at with Fida Ali. The third member of our trip,Mr Fasi ur rehman, was coming from Islamabad. He is very nice and funny guy perfect for such long trips.

We left at 9am and somewhere on the way after exiting Mansehra we stooped at a fruit shop and bought watermellon. It was so tasty and  Fasi asked the guy if it was injection free because in cities when the fruit is tasty we doubt always it .

Then we stared the journey and at a view point in Gadi Habib Ullah we stopped for  some photography. We witness the massive plantation under Billion Tree Tsunami (BTTP). It is really an amazing work been done by Imran Khan and team, specially in an area where there is abundance of tree and large extend of deforestation was going unnoticed. Imran Khan and team did exactly the opposite.

Then the journey started and our next stop was a point near Muzaffadabad. It was really an amazing  view to see the snake shaped river engulfing the city. The Hydro power station and the zigzag road going up on the mountain was also multiplying the beauty of the city.It is small city relatively but the beauty is beyond expression.

We descended and entered the city. Contrary to our expectation Muzaffarabad is very low altitude and very hot city. We did our lunch at Royal Continental Hotel and had some rest before resuming our journey. To make sure we don’t face any issue in our upcoming remote and long journey we went to mechanic to do a check up for our vehicle.

Our next destination was Neelum Valley.

( To be continued)

The Mighty Baha Lake in Khokush Nala Ghizer, Gilgit-Baltistan

I had been to home on my eid holidays and soon after the eid prayers my elder brother and his friends made plans to go on hiking and fishing to Baha Lake in khokush nala. I was also invited to join them. Although I was yet relieved of the exhaustion of the long drive from Lahore to home but I couldn’t refused as it was always my dream to go on such adventurous tours.

We reached at the lake site almost at mid night and  and camped there. The weather was not that much welcoming that night and in the morning we git up early as it was cold and everyone picked up there tools and went for fishing. I also took one and went to the lake site and there i witnessed majestic view of the lake. I was standing on a big foot of rock and wind was blowing fast. I could see the waves rising in the middle of the lake and coming towards the bank. In no time they stroke with the rocks and turned back. I stopped fishing and sit there for quite long just to enjoy this majestic view. I couldn’t describe it in any better in words so I am putting up the video which I had captured and you can view and enjoy it.



Funny Moments in Courts

Court room is always instantaneous with the lawyers always shooting question at opposite parties and on witnesses.  Sometimes there happen very funny moments in exchange of words from both sides, Here are some of the most funny moments recorded in courtrooms.

1) Some things just aren’t straightforward enough

ATTORNEY: How was your first marriage terminated?

WITNESS: By death…

ATTORNEY: And by whose death was it terminated?

WITNESS: Take a guess.

2) Using the oath as a perfect reason to make a joke

LAWYER: Now sir, I’m sure you are an intelligent and honest man–

WITNESS: Thank you. If I weren’t under oath, I’d return the compliment.

3) Some questions are just too complicated

LAWYER: When he went, had you gone and had she, if she wanted to and were able, for the time being excluding all the restraints on her not to go, gone also, would he have brought you, meaning you and she, with him to the station?

OTHER LAWYER: Objection. That question should be taken out and shot.


4) There’s never a reason not to make a pun

LAWYER: Doctor, did you say he was shot in the woods?

WITNESS: No, I said he was shot in the lumbar region.

5) Taking responses too literally

ATTORNEY: ALL your responses MUST be oral, OK? What school did you go to?


6) To be fair, those headlights are pretty flashy

LAWYER: Trooper, when you stopped the defendant, were your red and blue lights flashing?


LAWYER: Did the defendant say anything when she got out of her car?

WITNESS: Yes, sir.

LAWYER: What did she say?

WITNESS: ‘What disco am I at?’

7) Everything is possible

ATTORNEY: Doctor, before you performed the autopsy, did you check for a pulse?


ATTORNEY: Did you check for blood pressure?


ATTORNEY: Did you check for breathing?


ATTORNEY: So, then it is possible that the patient was alive when you began the autopsy?


ATTORNEY: How can you be so sure, Doctor?

WITNESS: Because his brain was sitting on my desk in a jar.

ATTORNEY: I see, but could the patient have still been alive, nevertheless?

WITNESS: Yes, it is possible that he could have been alive and practicing law.


8) I don’t think that’s how memory works

ATTORNEY: This myasthenia gravis, does it affect your memory at all?


ATTORNEY: And in what ways does it affect your memory?

WITNESS: I forget..

ATTORNEY: You forget? Can you give us an example of something you forgot?

9) Some people just simply aren’t good with numbers

ATTORNEY: How old is your son, the one living with you?

WITNESS: Thirty-eight or thirty-five, I can’t remember which.

ATTORNEY: How long has he lived with you?

WITNESS: Forty-five years.

10) Technically, it’s not wrong, which is the best type of being right

ATTORNEY: What is your date of birth?

WITNESS: July 18th.

ATTORNEY: What year?

WITNESS: Every year.

11) That one must’ve hurt…

ATTORNEY: The youngest son, the 20-year-old, how old is he?

WITNESS: He’s 20, much like your IQ.

12) Details matter

LAWYER: Any suggestions as to what prevented this from being a murder trial instead of an attempted murder trial?

WITNESS: The victim lived.

13) This seems like a trick question

LAWYER: You were there until the time you left, is that true?

14) Using the right to remain silent isn’t always the brightest idea

LAWYER: Did you ever stay all night with this man in New York?

WITNESS: I refuse to answer that question.

LAWYER: Did you ever stay all night with this man in Chicago?

WITNESS: I refuse to answer that question.

LAWYER: Did you ever stay all night with this man in Miami?


Judge and lawyers in courtroom

15) This is when you need to switch attorneys

ATTORNEY: She had three children, right?


ATTORNEY: How many were boys?


ATTORNEY: Were there any girls?

WITNESS: Your Honor, I think I need a different attorney. Can I get a new attorney?

This post has been copied from shareably