dcs & plc

[TimeFluxCap]

TimeFluxCap,

If you plan to upgrade use the latest version CS3000 3.07 version. This run on a Ethernet platform.

Is that the gigabit ethernet? Now that is fast!

 

[labingtone]

yes it support gigabit ethernet.

 

[mpkashyap]

Selection Criterion for PLC and DCS

please help me out
difference between plc & dcs with example

PLC Preferred when:

• Equipment will be located on the plant floor
• More than one “cell” or “subsystem”
• Highly distributed I/O and controllers
• OEM’s involved
• Local operator interface desired
• Third party interfacing required
• Large discrete content or good mix of discrete and analog control with small amount of complex batch, blending, or multi-variable analog control
• Cost differential is an issue

DCS Preferred when:

• OEM’s not involved
• Large number of operator consoles desired
• Small amount of third party interfacing required
• Large amount of complex batch, blending, or Multi-loop analog control
• Plant “advanced” control/optimization required
• Non-time critical discrete/sequential control
• Cost (both installed and maintenance )is not a concern

 

[SIR]

Hi, all.
This is my first post here, so be gentil.

As I was looking for topics about the differences between PLC (with SCADA) and DCS, I mostly see that the discussion is HW-related.

For my job I'am working with both systems(more PLC + SCADA then DCS), and I'am convinced that one of the main differences is the software aspect.

If I have to compaire the both systems, from a programming point of view, I see the following main differences (correct me if i'am wrong):

1) Database
PLC + SCADA => 2 databases (1 for PLC and 1 for SCADA, which should be more or less identical copies)
DCS => 1 database for control and supervision

2) Standard software functions (e.g. motor logic and symbol)
PLC + SCADA => 2 standards (1 for PLC and 1 for SCADA)
DCS => 1 standard

3) Software execution and I/O handling
PLC => scan based
DCS => time based

4) Programming concept
PLC + SCADA => programmation has to be done in both parts seperatly. e.g. first the PLC program and then the SCADA software
DCS => putting something on the supervision screen automatically generates a standard function block in the control part of the DCS. Then it's just a matter of assigning I/O's to that function block.

 

[dandrade]

In this topic it includes the subject. I add a parcel here, therefore the commentary will be adjusted to the this topic.

http://www.plctalk.net/qanda/showthread.php?t=15765
BY LJAM
Most of the confusion comes from the roots of both systems. PLC were first created for and by electrical engineers to replace electrical relay panels (I believe GM engineers start it all). On the other hand, DCS systems were developed to replace pneumatic controllers … initially with logic performed by integrated circuit in cards and later by microprocessors.

As a user of both systems for the pass 15 years, I have seen how technological advances have draw closer together both systems to the point that many DCS’s manufacturer are talking about hybrid systems (i.e. Honeywell Experion PKS: Allen-Bradley Contrologix hardware and Honeywell firmware) … Emerson Fisher-Rousemount Delta V is another example of a hybrid system. Hybrid systems target medium size applications and compete with medium to large PLC systems.

In my opinion the gap between the two technologies was reduced considerably by improvements in the communication and networking capabilities of PLC’s, along with the raising in popularity of field buses (which also imply the usage of better and faster processors).


PLC’s still are the preferred system for control applications in manufacturing environments where sequencing and interlocking are the main concern. DCS’s are and will be (for the years to come) the preferred system for control systems at the top end of the process industry (i.e. we commissioned and thermal power plant of 60,000 tags). The middle point between those two is where both systems fight for supremacy.

The main points to consider before making a decision on whether use one or the other are:

§ The system number of tags and I/O (system capabilities).

§ Control strategies and the right engineering tools (the right tool will make the engineer easier and faster).

§ Hardware and support cost.

Very clarified well. LJAM must appear more frequent
Good for knowing that pneumatics always originated the DCS. The points of idea system:

• DCS simple and complex analogical systems.
• PLC discrete and analogical systems (simple)

DCS- Advanced Resources for analogic treatment:

• PWM, SFK and other resources to evaluate analogic signals in the domain of the time and frequency.

Is true features? I never visualized a manual of the DCS instructions...
Manual exist in Digital format?

By SIR
3) Software execution and I/O handling
PLC => scan based
DCS => time based

Time based?!? How to work method?

 

[Smoker113]

I work with both and simply put (in my limited knowledge):

PLCs - Scale down better, they can be installed standalone or as part of a network.
DO NOT usually come with an HMI/historian etc.
Fast scan rate, great for logic solving/interlocks and general automation.
Runs into problems on big systems (50,000 IO plus).
Any segementation has to be designed and set up by the system integrator, this in itself is not part of the PLC side, but done in something like Intellution or Wonderware.

DCS - Requires substantial set-up costs!
You need several parts just so the system can run.
Comes with lots of pre-built goodies such as alarm annunciation, HMIs & historisation.
Great for regulatory PID control, supervisory and advanced control apps.
Can handle BIG installations well due how the manufacturer allows segmentation the network.

In summary PLCs tend to be more flexible in what they can do, but require the integrator to BUILD everything from scratch.
DCS comes with alot more 'canned' stuff and as such has the tools to manage a much larger scaled system.

The line is getting blurry tho!
Honeywells C200 controller looks remarkably familiar......

http://hpsweb.honeywell.com/NR/rdonlyres/E43FF645-248A-4D1D-80AF-0EA80DC4CF1A/0/ControlExeEnvironC200.jpg

 

[undercontrol]

At the beginning : DCS more likely suitable for process control and PLC more likely to discrete control.

Nowadays : PLC function is going more & more to be like DCS

 

[omer53]

Actually i was trying to understand the diffrence between PLC &
DCS. but i still could'nt find a solid answer about it.

is it
DCS is for PID controls
PLC is for basic controls like Analog and digital I/O s but (which can also done by DCS too.

what else a dcs can do which a PLC cant
...
really need your help
thankx is Advance

 

[SLC_Integrator]

TimeFluxCap,

If you plan to upgrade use the latest version CS3000 3.07 version. This run on a Ethernet platform.

Its actually 3.08
It does run on gigbit ethernet (VNet IP) and its a joy to do work on.

I have a complete system set up in our staging room next to my office ready to go to a customers site for a refinery DCS replacement we are doing.

Its been a while since this thread and after re-reading it I guess one thing is some folks should really go and work on a system before they comment on it!

As for my views:

Yes!

Old DCS systems DO suck to work on because they are stupidly expensive, completely user vicious and a real PITA to backup or document.
On the other hand when these systems were put in, PLC were expensive, huge and extremely limited. Windows didnt exist and HMIs were unheard of. Folks had the choice to either stick with pneumatics and their associated problems or put in a TDC2000/RS3/Provox/Infi90/XL.

Now folks are finding that these legacy systems are coming to the end of their life and we are seeing alot of demand to rip out and replace. Alot of Delta V and CS3000 is going in with the odd Experion system for those Honeywell lovers.

 

[MikeW]

Actually i was trying to understand the diffrence between PLC &
DCS. but i still could'nt find a solid answer about it.

is it
DCS is for PID controls
PLC is for basic controls like Analog and digital I/O s but (which can also done by DCS too.

what else a dcs can do which a PLC cant
...
really need your help
thankx is Advance

As others have stated on this old topic, both can control an application (PID and/or simple logic), it depends on what you want: (This may be an overly gross simplification in some cases)

Pay a lower cost for the hardware initially for a PLC and then possibly spend many hours (and possibly increase the total cost)developing all the functions required to make the hardware work.

Pay more upfront for hardware and operating system software for a DCS but many programming functions may be easily added (operator GUI interface, PID loop setup and plotting, easier networking/ data historian, etc)

DCS can be expanded into a large system with lots of IO and PLC are typically the choice is a small system with limited IO.

 

[farrei]

think

i think dcs if you r talking about siemens its very tricky because siemens plc is also doing the work of dcs but when you talking about generaly dcs is the system that can handle with analoge values in which you caqn store ,maninpulat and display is called dcs and plc is only for digital values evry brand other than siemens having there seperate system for dcs but siemens combine both things i heard from many people that siemens dont have dcs system but my thinking is that siemens make both combine if some one has ojection then we can do more discusion on that topic