Seven Ways Today’s Distributed Control Systems (DCS) Can Save You 20% or More In the past, DCS Systems were large, expensive and very complex. This drove many control engineers to use Programmable Logic Controllers (PLCs) and Human Machine Interface (HMI) in order to lower cost. Today, these implementations are consistently more expensive than DCS systems for the same process or batch application. This report documents the key advantages of DCS systems over PLC/HMI engineered systems and the typical value of each.
Executive Summary This report has been developed to help show how you can significantly reduce the cost of your process automation. As you probably know, integrating independent PLC’s and required operator interface, takes a great amount of time and effort. This effort is focused on making the technology work together, rather than improving operations, reducing costs, or improving the quality or profitability of your plant. Many engineers do not normally think about it but a PLC/HMI system may have a subset, if not all, of the following unique and manually coordinated databases. • Each controller and its associated I/O • HMI (potentially multiple HMIs) • Alarm Management • Batch / Recipe and PLI • Redundancy at all levels • Historian • Asset Optimization • Fieldbus device management Each of these databases must be manually kept in sync. Every time a change is made in one, others usually need to be updated to reflect the change. For example, when an I/O point and some control logic is added you probably need to change or add a HMI element, the Historian and the Alarm database. This means your engineers must make these changes in each of these databases, not just one. In another scenario a change may be made in an alarm setting in a control loop. In a PLC implementation there is no automatic connection between the PLC and the HMI. This can be a large problem during start up of a new application where alarm limits are being constantly tweaked in the controller to work out the process while trying to keep the Alarm Management and HMI applications up to date with the changes and useful to the operator. Key Advantages Today’s DCS systems (also known as Process Control Systems) are developed to allow you to quickly implement the entire system by integrating all of these databases into one which is designed, configured and operated from the same application. The table below explains how savings can be realized by using today’s DCS System over a PLC/HMI system. This information has been collected from decades of implementation expertise of ABB engineers, end user controls engineers, consultants, and multiple Systems Integrators who actively implement both types of control solutions based on application requirement and user preferences. Page 2
PLC/HMI Process Control System *Time savings (DCS) with Process Control Engineering Control Engineers must map As control logic is 15‐25% out system integration designed, alarming, HMI depending on between HMI, alarming, and system how much controller communications, communications are HMI and and multiple controllers for automatically configured. alarming is every new project. being One software designed into Control addresses (tags) configuration tool is used the system. must be manually mapped in to set up one database engineering documents to used by all system the rest of the system. components. This manual process is time As the Control Engineer consuming and error prone. designs the control logic, the rest of the system falls Engineers also have to learn into place. multiple software tools, which can often take weeks The simplicity of this of time. approach allows engineers to understand this environment in a matter of a few days. Programming Control logic, alarming, When control logic is 15%‐45% system communications and developed, HMI HMI are programmed Faceplates, alarms and independently. Control system communications Engineers are responsible to are automatically integrate/link multiple configured. databases to create the system. Faceplates automatically appear using the same Items to be manually alarm levels and scalability duplicated in every element set up in the control logic. of the system include. These critical data ‐ Scalability data elements are only set up ‐ Alarm levels once in the system. ‐ Tag locations (addresses) This substantially reduces the time it takes to Only basic control is engineer and implement a available. Extensions in system and errors in the functionality needs to be system. Page 3
PLC/HMI Process Control System *Time savings (DCS) with Process Control created on a per application basis. (e.g. Feed Forward, This is analogous to having Tracking, Self tuning, your calendars on your Alarming…) This approach desktop and phone leads to non‐standard automatically sync vs. applications, which are having to retype every tedious to operate and appointment in both maintain. devices. People who try to keep two calendars in sync Redundancy is rarely used manually find it takes with PLC’s. One reason is the twice the time and the difficulty in setting it up and calendars are rarely ever in managing meaningful sync. redundancy for the application. Redundancy is set up in software quickly and easily, nearly with a click of a button. Commissioning Testing a PLC / HMI system is Process Control Systems 10‐20% and Start up normally conducted on the come with the ability to depending on job site after all of the wiring automatically simulate the the complexity is completed and the process based on the logic, of the start up production manager is asking HMI and alarms that are and “why is the system not going to be used by the commissioning running yet?” operator at the plant. Off line simulation is This saves significant time possible, but this takes an on‐site since the extensive effort of programming has already programming to write code been tested before the which will simulates the wiring is begun. application you are controlling. Due to the high cost and complex programming, this is rarely done. Troubleshooting Powerful troubleshooting All information is 10‐40% tools are available for use if automatically available to (Varies greatly the controls engineer the operator based on the based on the programs them into the logic being executed in the time spent system. controllers. developing HMI and Page 4
PLC/HMI Process Control System *Time savings (DCS) with Process Control For example, if an input or This greatly reduces the alarming, and output is connected to the time it takes to identify keeping the system, the control logic will the issues and get your system up to be programmed into utilize facility up and running date.) the control point. But when again. this is updated, did the data get linked to the desperate The operator also has HMI? Have alarms been set access to view the up to alert operators of graphical function blocks problems? Are these points as they run to see what is being communicated to the working and not. (read other controllers? only) Programming logic is rarely Root Cause Analysis is exposed to the operator standard. since it is in a different software tool and not Field Device diagnostics intuitive for an operator to (HART and Fieldbus) are understand. available from the operator console. Ability to change Changing the control logic to Adding or changing logic in 20‐25% to meet process meet new application the system is also very savings on requirements requirements is relatively easy. In many cases even changes is not easy. The challenge comes easier to change logic with uncommon. with additional requirements built in and custom to integrate the new libraries of code. functionality to the Operator Stations. Also, When changes are made, documentation should be the data entered into the developed for every change. control logic is This does not happen as automatically propagated much as it should. to all aspects of the system. This means far less If you were to change an errors and the “system” input point to a new address has been changed with or tag, that change must be just a single change in the manually propagated control logic. throughout the system. Operator Operator Training is the Training for operators is 10‐15% is Training responsibility of the available from the process common in developer of the application. control vendor. This is due training costs Page 5
PLC/HMI Process Control System *Time savings (DCS) with Process Control There is no operator training to the standardized way reduction, but from the vendor since every information is presented this can be faceplate, HMI screen or to operators. magnified Alarm management function with the can be set up differently This can significantly constancy from the next. Even within a reduce operator training found across single application operators costs and quality due to operators. could see different graphics the common and expected for different areas of the operator interface on any application they are application, no matter monitoring. who implements the system. System Documentation is based on As the control logic is 30‐50% due to documentation each part of the overall changed, documentation the nature of system. As each element is for all aspects of the the system changed, documentation system is automatically being put in must be created to keep created. place. each document up to date. Again, this rarely happens, causing many issues with future changes and troubleshooting. * Time savings based on typical costs associated with a system using ~500 I/O, Two controllers, One workstation and 25 PID Loops. Page 6
Your Customized Results As you know, these are “typical savings”. Your individual savings will vary from the estimates, and may vary greatly. To help you determine the savings for your application we have two tools to assist you. 1) A self help tool, the Custom Process Evaluation Worksheet (can be found at http://www.abbprocess.com/files/Process_Eval_Worksheet.xls). After you download this tool you will be able to change the cells highlighted in yellow to give you an idea where the savings can be found in your application. An example of the worksheet is shown below. Sample Process Application 2 Controllers, 500 I/O with 25 PID loops, One Workstation which also monitors other parts of the facility Project Phase PLC / HMI Process Control System Hours $/Hour Cost Typical Savings Cost Engineering 210 $120 $25,200 20% $20,160 Purchase Price N/A N/A $45,000 0% $45,000 Programming/Implementation 160 $120 $19,200 45% $10,560 Installation/wiring 200 $120 $24,000 0% $24,000 Integration 60 $120 $7,200 95% $360 Commissioning 20 $120 $2,400 40% $1,440 Troubleshooting (cost per hour 10 $10,000 $100,000 20% $80,000 includes plant downtime) Upgrade the process 100 $120 $12,000 45% $6,600 Training / Documentation 60 $120 $7,200 50% $3,600 Total $242,200 21% $191,720 2) Our local ABB Process Control Expert can be contacted to deliver a “Custom Process Evaluation” and assist you in the completion of the worksheet. Many engineers find this 20‐30 minute discussion helpful since our experts understand both the DCS and PLC/HMI architectures well and can help you understand where the savings shown in the worksheet really comes from. To find your local rep, please call 800 435 7365, option #2, then #5. Conclusion If you are using PLC’s and HMI to control your process or batch applications, your application is a great candidate to reduce costs and gain better control. Your savings would be significant and will continue to lower your costs over the life of your system. We look forward to helping you identify these savings and realize them in your next implementation. Page 7