Blog Archive
PLC vs. DCS
At EPIC Automation, every practical, beneficial and cost-efficient automation solution we develop is based upon industry research and trends. Before any design or development takes place, our engineers take the time to research and gain a thorough understanding of the process. In October of 2011, Bill Lydon, Editor of Automation.com wrote an article called "PLC vs. DCS - Competing Process Control Philosophy". Below we have built a table of the differences he sees between the two controls platforms:
|
|
PLC |
DCS |
Common Applications |
Non-core process functions including material handling, water treatment, motor controls, balance of plant operations, air compressor controls, packaging, and other functions |
Core processes (food, pharmaceutical, refining, etc.) |
Control Architecture |
Programming Model “Loose” component architectures allowing functions to be easily added with hardware and software |
Configuration Model Multi-disciplined controllers for logic, sequential and process control, HMIs, custom applications, and business integration on one platform. |
Price |
No Significant Difference Competitive with DCS |
No Significant Difference Competitive with PLC |
Enterprise Interface |
PLC applications have caught up to DCS in recent years and most interface to business enterprise systems for information interchange and synchronized operations |
DCS systems have tied into the enterprise for years, conforming to the Purdue Model and more recently the ISA95 standard |
Asset Management |
PLCs are playing catch up |
Provide integrated software for a full range of devices and asset management standards |
APC Advanced Process Control |
Beginning to add functions and break into process control |
Offer a number of tools for optimizing control loops and more advanced alternatives to improve performance of PID control. |
Total Production Optimization |
Can be approximated with loosely coupled software add-ons |
Real-time software modeling and control optimization is an emerging function |
Sensor/Control Network Communications |
PLC systems tend to have less refined interfaces to Foundation Fieldbus and HART. In many cases they rely on third party hardware and software with configuration being more labor intensive. |
DCSs have highly refined and integrated interfaces to Foundation Fieldbus and HART and adequate interfaces to other industrial automation networks |
DCS Backbone Network |
PLC systems use open published protocols that are designed to cover a wide range of applications including simple discrete, synchronized motion control, motor control, and process. PLC suppliers continue to add options for redundancy. All control functions can connect to one Ethernet backbone (process control, discrete, motion control, safety; etc.) |
In DCS systems, the process networks (Foundation Fieldbus, HART) and PLC-oriented networks (DeviceNet, Profibus, Modbus, etc.) are connected to controllers, which are connected to the process DCS backbone. DCS systems generally have easier to apply redundancy solutions but the open networking standard groups such as ODVA and PI International have defined solutions for their protocols particularly with the initiatives for networked machine safety. |
Skid & Packaged Systems |
Provided by skid vendor. Usually require field engineering to configure and maintain |
N/A |
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Comments
Frank Says:
February 16, 2012 at 08:16 AM
I just reviewed your blog table and have a few comments. You will get different inputs from people based on their industry slant so I will try to be unbiased. I’ll just give you the facts.
Common applications – I spent the last couple years taking out a couple of legacy DCS systems and replacing them with PLC control. The control works just fine and the maintenance guys like the ability to understand the simpler control when they need to make changes.
Price – the hardware prices might be competitive but the per point yearly software licensing pricing of the DCS is significantly higher.
Sensor / Communication Networks and Asset Management – The systems I just put in included HART natively into the I/O cards and software and also accessed through the backplane over the plant network by the same asset management system that was doing it through the DCS using multiplex cards. We used this feature a lot during startup. Modbus has always been a no-brainer in PLCS which DCSs adopted. ODVA (also called Devicenet) and EthernetIP started out in the PLC world and was adopted by the DCSs. The same PLC has FF and Profibus communication, but since I have no experience yet with it I can’t say how refined it is but I suspect it probably works if you get the right drivers. There is a war going on with companies trying to keep some of the driver properties proprietary to their equipment while saying they are totally open. Mostly it’s a lot of marketing games.
Marvin Says:
February 03, 2012 at 09:35 AM
I like the table format, very easy to read. I’m personally inclined to PLC’s but there many advantages to the DCS platform.
Spud Says:
February 02, 2012 at 06:56 AM
Ah, i see. Well that’s not too ticrky at all!”
Gabrielle Says:
January 26, 2012 at 10:30 AM
I have exactly what info I want. Check, palese. Wait, it’s free? Awesome!
Mickey Says:
January 19, 2012 at 08:51 AM
Posts like this brigthen up my day. Thanks for taking the time.