Distributed Control System (DCS) Explained

What is a DCS?

A Distributed Control System (DCS) is a computerized control system that streamlines the functionalities of industrial devices used throughout a workspace. A DCS utilizes a wide range of controllers to permit all the parts to converse with one another just as PCs do. These controllers are distributed geographically across a plant to allow for high-speed communication to the control process. When utilizing various kinds of modules, the framework may require diverse correspondence norms, for example, Modbus and Profibus.

What is a Distributed Control System
Distributed Control System Layout
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A PLC installed alongside other components

What Is a PLC (Programmable Logic Controller)?

What Does “PLC” Stand For?

A Programmable Logic Controller, abbreviated as “PLC” is a computer used to address the issues of a particular assembling process. These devices come in a wide range of shapes and sizes, with numerous alternatives for computerized and simple I/O, as well as protection from high temperatures, vibration, and electrical noise. The invention of the PLC allows for computers to be streamlined into the industrial automation process.

A PLC can be a solitary device figuring and executing operations, or a rack of various modules utilized to meet whatever your automation system requires. A portion of the extra parts include processors, power supplies, additional IO, interfaces, and more. Each part cooperates to have the option to run open or shut circle activities that are appraised at fast and high accuracy. Take a CNC machine for instance; a PLC would be utilized to control positioning, motion, and torque control. These devices are popular since they are inexpensive in relation to the amount of power and lifespan they possess. PLCs can run for hours on end. 

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PLC vs. DCS: What’s the difference?

Before we get into the differences of a PLC’s and DCS’s, we need to talk about what each of them are designed to do.

What is a PLC?

A PLC, or Programmable Logic Controller, is a computer that has been adapted to specifically meet the needs of any specific manufacturing process. These devices come in many different shapes and sizes, with many options for digital and analog I/O, as well as protection from high temperatures, vibration, and electrical noise. The invention of the PLC allowed computers to be streamlined into the industrial automation process.

A PLC can be a single device calculating and executing operations, or a rack of different modules may be used to meet whatever your automation system requires. Some of the additional components include processors, power supplies, additional IO, interfaces, and much more.  Every part works together to be able to run open or closed loop operations that are rated at high speed and high precision. Take a CNC machine for example; a PLC would be used to control positioning and motion, as well as torque control. These devices are popular because they are very inexpensive relative to the amount of power and how many hours you get out of them.

 What is a DCS?

A Distributed Control System is an automated control system that streamlines the functionalities of the various devices that are used throughout an entire work space. This type of system uses many different controllers to allow all the machining parts to talk to each other as well as computers that can input parameters and display information such as power usage, speed, and much more. These controllers are distributed geographically across a plant to allow for high-speed communication to the control room. When using different types of modules however, the system may require different communication standards such as Modbus and Profibus. DCS’s started coming to fruition throughout the 1960’s once the microcomputer was brought widespread into the market.

Then what exactly is the difference?

A PLC will probably be used to control a machine that isn’t too complex wheres the DCS can have total control of all the operations in an entire plant. The PLC is preferred in situations where the machine does not have to worry about meeting specific conditions inside the plant. These conditions typically involve operations that may need to stop or restart, as well maintaining precise temperatures. A DCS will be able to take advantage of all the aspects of an automated system, from the machines and sensors to the controllers and computers. An entire DCS is much more expensive than a few PLC’s, but each have their advantages in any given situation and certain automated systems will always require one over the other.

Visit MRO Electric and Supply’s website to see all of our available Programmable Logic Controllers. If we don’t have what you need listed on the site, contact us at sales@mroelectric.com or (800)691-8511 and we will be happy to help.

Modicon PLC History

Richard E. Morley, also known as Dick, was an American electrical engineer. He was an employee at Bedford and Associates, located in Massachusetts. He is most commonly known for his involvement with the production of the first Programmable Logic Controller (PLC) for General Motors and the Modicon in 1968. General Motors Company, often referred to as GM, is an American multinational corporation that is headquartered in Detroit, Michigan that engineers, manufactures, markets and distributes vehicles and vehicle parts and sells financial services.

Known as an author, educator, influencer and specialized engineer, Morleys’ accomplishments and contributions have earned him numerous awards from families such as ISA (the instrumentation systems and automation society), Inc. Magazine, Franklin Institute, SME (the Society of Manufacturing Engineers), and the Engineering Society of Detroit. SME offers the Richard E. Morley Outstanding Young Manufacturing Engineer Award for outstanding technical accomplishments in the manufacturing space by engineers age 35 and younger.

Schneider Electric currently owns the Modicon brand of PLCs. The PLC has been recognized as a major advancement in the automation space and has had an unprecedented impact on the manufacturing community as a whole. PLCs were designed to replace re-wiring and hard-wired control panels with software program changes when production updates were necessary. Before PLCs came about, several relays, drum sequencers, cam timers and closed-loop controllers were used to manufacture vehicles and vehicle parts. Re-wiring the relays and other necessary components was a very in-depth and costly process, but clearly worth the effort. The Modicon 084 PLC was modeled to be programmed in ‘ladder logic’ which had the look of the schematic diagrams of relay logic it was replacing.  This made the transition to PLCs easier for engineers and other professionals in the manufacturing space.  The automotive industry is still one of, if not the largest users of PLCs today. MRO Electric and Supply has new and refurbished Modicon parts available including the Modicon Quantum series. We also offer repair pricing. For more information, please call 800-691-8511 or email sales@mroelectric.com.

Modicon PLC History

The Modicon PLC Timeline

A few years later, in the 1970’s, dialogue between PLCs came about. Introduced as the first industrial communications network, Modbus was based on a Slave/Master architecture that used messaging to communicate between Modbus nodes. All and all, a lacking standardization made PLC communications a nightmare.

In the  1980’s, General Electric made an effort to regiment the interconnection of devices from several manufacturers with MAP (manufacturing automation protocol). PLC programming software was also created to operate on personal as well as professional computers in order to remove the need for dedicated programming terminals or handheld programmers.

As years have gone on, PLCs have evolved as technology evolves. Nowadays, they include process, motion, and distributed control systems, as well as complex networking. Equivalent to an average, run-of-the-mill desktop computer, PLCs have capacities for data handling storage and impressive processing power.

PLC Security

Programmable logic controllers, also known as PLCs, initially came about in the late 1960s. PLCs were designed to replace relay-based machine control systems in the major U.S. vehicle manufacturing space. The relay-based control systems were considered hard to use and were disliked amongst those in the automation and manufacturing in.

In 1968, Dick Morley of Bedford Associates in Massachusetts designed the Modular Digital Controller, later dubbed the Modicon. After the Modicon 084’s initiation into the world, there was no looking back to those relay-based control systems. Be sure to check out our article covering Modicon PLC history to learn more.

PLCs are user-friendly microprocessor-based specialty computers that carry out control functions, many of which are of high levels of complexity. They are engineered to endure harsh and strenuous situations such as in heated, cooled and even moist environments. Used for automation usually in the industrial electromechanical space, PLCs are computers that deal with the controlling of machinery, often on  the following:

  • factory assembly lines
  • power stations
  • distribution systems
  • power generation systems
  • gas turbines

PLCs are programmed using a computer language. Written on a computer, the program is then downloaded to the PLC via a cable. These programs are stored in the PLCs memory. The hard-wired logic is exchanged for the program fed by its user during the transition between relay controls to PLC. The manufacturing and process control industries have gotten to take advantage of PLC applications-oriented software since Modicon PLCs inception.

plc security
PLC Functions and Directions

PLCs use programmable memory in order to store particular functions and directions. Some functions and directions would include:

  • on control
  • off control
  • timing
  • sequencing
  • counting
  • arithmetic
  • data manipulation
PLC Types

Understanding the different types of PLCs will be very helpful when looking into PLC security.

The numerous types of PLCs can be organized into three principal categories:

  • Advanced PLC: Advanced PLCs offer the greatest processing power out of all of the PLC types. They feature a larger memory capacity, higher input/output (I/O) expandability, and greater networking options.
  • Compact Controller: Logic Controllers are increased intermediate level offerings with an increased set of instructions and a greater input/output (I/O) than a run-of-the-mill logic controller
  • Logic Controler: A logic controller is often referred to as a ‘smart relay’. They are generally straightforward to use and considered a good place to begin when becoming acquainted with PLCs. They are cost-effective for low input/output (I/O), slower speed applications.
PLC Security

As security concerns remain in many professional spaces including the factory automation space, becoming up-to-speed with the different types of PLC Security is imperative. By creating and implementing an effective strategy to remain secure, you will likely avoid issues, downtime, and setbacks. Understanding the different types of PLCs will be very helpful when looking into PLC security.

PLC Cybersecurity: How the control network is linked to the internet, as well as other networks. A handful of PLC issues could likely involve the following:

  • Incident response planning and plans;
  • Issues drafting and reviewing policies
  • Issues drafting and reviewing procedures
  • Retention of cybersecurity experts and vendors;
  • A need for preparation of a breach:
    • exercises
    • training
    • breach simulations
  • A need for cybersecurity insurance review and counseling
  • A demand for record management and information infrastructure;
  • Privacy risk management
  • Assessment of cybersecurity risk in mergers and acquisitions;
  • Payment Credit Industry (PCI) Compliance protocols
  • Vendor contract management protocols
  • Supply chain risk management

PLC Physical Security: Although PLC physical security differs from PLC cybersecurity, it is still important and should be prioritized when an individual or a company is undergoing breach simulations, training, and exercises. PLC physical security deals with:

  • correcting default passwords
  • ensuring only certified individuals are in the control system’s environment
  • limiting access to thumb drives and securing access

MRO Electric and Supply maintains a comprehensive stock of Modicon PLC parts, including the Modicon Quantum series. Also, feel free to check out our repair and core exchange programs to learn how to save.

Understanding Issues with Security
In order to create and implement training and procedures for staff, you must understand how issues with security occur.  Not all cybersecurity attacks occur from external hackers or scammers. In fact, experts believe that only an estimated 20% of all cybersecurity attacks are intentional and intended to be malicious. Whether you think it’s possible or not, an offended employee could indeed be your hacker. Almost always caused by software issues, device issues, and malware infections, cybersecurity seems straight-forward initially, until you dig into those fine, often overlooked details.

As many in the automation space may know, PLC cybersecurity wasn’t a thing a decade ago. These days, PLCs are connected to business systems through any run-of-the-mill network and aren’t separated from other networks that other automation equipment may also be on.  As time goes on, it’s becoming more and more common to see TCP/IP networking from a business system standpoint. By connecting via TCP/IP, data exchange, as well as more rational and scalable business decisions, is enabled.

PLC Security Factors:
  • Although it may not actually connect to the internet, a control system is unsafe. Contrary to popular belief, a modem connection could also experience intrusion and a hack.
  • Wireless networks, laptop computers, and trusted vendor connections could be other sources of connections in which people may be likely to overlook.
  • Keep in mind that the majority of IT departments are unaware of factory automation equipment, including CNCs, CPUs, PCBs, robotics parts and, last but not least, PLCs.
  • Piggybacking off of the last point, IT departments’ lack of experience with the aforementioned equipment, along with their lack of experience with industrial standards and scalable processes indicate that they should not be in-charge and responsible for a company’s PLC security. Nobody wants an annoyed employee to make inappropriate changes to a PLC’s communication highway.
  • Hackers do not necessarily need to understand PLC or SCADA to block PC-to-PLC communication. They absolutely do not need to understand a PLC or SCADA system to cause operational or programming issues.
  •  Often times, control systems, including ones that many PLCs integrate with, use Microsoft Windows, which is very popular amongst hackers.
  • Some PLCs crash simply by pinging an IP address, like what happened at the Brown’s Ferry Nuclear Plant, which is located in upstate Alabama. Since the incident in 2006, the plant has undergone numerous security, operational, and management improvements.

In conclusion, when a security breach occurs, regardless of the specifics, understanding that time is of the essence will help smooth over most incidents. Trusting who has access to a control systems environment and thumb drive is crucial. If someone has access to the control system environment and thumb drive, ensure they’re well-qualified and up-to-speed with their team and/or company.

Choosing the most appropriate PLC

As many machine automation professionals know, deciding on which PLC to work with can be one of the most difficult decisions you have to make when organizing your control system.  There is no one size fits all equation, so are here are some guidelines I use.

Brand –   Many of the major players such as have small, medium, and large-scale PLCs.  Always consider when brands the end user already is using.  Things will always go smoother if the maintenance personnel is already accustomed to the brand of PLC you choose.  Also, try to pick a brand that will have stellar local support for the end user if you are not in the area.

Sizing – Sizing a PLC is imperative to the success of your project.  If you go too small,  you may max out your I/O (such as this Modicon Quantum I/O)on changes and additions.  On the other hand, if you go too large,  you may blow go over your budget. Leaving room for expansion is ideal, but, in the long run, going over your budget is not practical.

  • Count up your:
    • Discrete input points
    • Discrete output points
    • Analog input points
    • Analog output points
  • Communications.   regularly have a port available on the PLC to communicate with it from your laptop without disconnecting other devices.  With modern PLCs with several communications methods, there is no reason for this to happen.
    • Will you need remote I/O?  This can reduce installation time and troubleshooting in the long term.
    • Will your system utilize an HMI?  How will you communicate with it?
    • Having a way to remotely monitor your PLC is becoming standard practice.

MRO Electric and Supply has new and refurbished Omron and Siemens products available. We also offer repair pricing. For more information, please call 800-691-8511 or email sales@mroelectric.com.

plc

How to maintain a PLC (Programmable Logic Controller)

Updated: June 2024

Proper maintenance of Programmable Logic Controllers (PLCs) is crucial to ensuring they continue to function efficiently and reliably. Routine PLC maintenance involves tasks such as checking for wear and tear, replacing defective components, and consistently updating the software. This proactive approach not only extends the lifespan of PLCs but also helps in avoiding unexpected downtimes and costly repairs. Additionally, maintaining PLCs plays a key role in predictive maintenance, leveraging data and analytics to foresee potential equipment failures and schedule timely interventions. By adhering to a consistent maintenance routine, industries can enhance their operational efficiency and safeguard their investments in automation technology.

Why is PLC Maintenance Important?

PLCs (programmable logic controllers) are such an integral part of the automation world, and in turn a major contributor to the industrial market. Downtime can be incredibly costly, and finding parts for legacy units can be difficult and time consuming. (MRO Electric sells many legacy and discontinued automation components, from top brands) Therefore, properly maintaining your PLC can avoid unnecessary headaches and get the most life out of your units.

Pre-Maintenance Checklist

Before starting preventative maintenance on your PLC, make sure to do the following:

  1. Back up your PLC program prior to getting your hands dirty (it’s also a good idea to always keep a master copy of operating programs on hand).
  2. Follow proper lockout/tagout procedures.
  3. Remove power from the system. Power should always be off and unplugged during maintenance.
  4. Audit all parts in use.

PLC Maintenance Procedures

This is a good guidebook to use when performing preventive PLC maintenance:

  1. Check environmental factors / operating conditions. Humidity, temperature and other factors play an important role in the longevity and proper operation of your components. Be sure that these factors are consistently within the range of your PLCs optimal operating conditions.
  2. Clear debris, dust, and buildup from your units. A clean working environment for your PLC is a great way to prevent downtime. Also, dust getting to the circuit boards could cause a catastrophic short circuit.
  3. Clean or replace all filters installed in enclosures. This allows your PLC to get the maximum airflow and ensures consistency.
  4. Check all your connections for a tight fit, especially I/O modules. This is a very simple way to make sure everything is working smoothly. Also, a loose connection may cause lasting damage to your components.
  5. Inspect I/O devices for proper adjustments.
  6. Check LED battery indicators on the RAM memory module in the CPU. If the OK LED is on or flashing, replace the battery ASAP.

Other Things to Keep in Mind

  1. Calibrate circuit cards with process control analogs every 6 months.
  2. Service devices such as sensors every month.
  3. Never place other pieces of equipment that produce lots of noise or heat close to your PLC.

How to maintain a PLC (Programmable Logic Controller)

As many of us know, PLCs (programmable logic controllers) are staples in the factory automation world. In order to have them running optimally and as efficiently as possible, routine maintenance is imperative. Generally, manufacturers produce PLCs to endure strenuous, unsterilized environments. By adhering to an adequate maintenance schedule, PLCs operating timeframe can be lengthened.

Protect your PLC

Always be on the lookout for corrosive and conductive contaminants that have the potential to become a detriment to a PLCs’ components. By completing visual inspections for black dust and blowing airborne particles from the PLC’s vicinity, you are lowering the likelihood of contamination.

Is power flowing?

A PLC will not operate correctly without adequate power. To avoid any operation bugs, remain vigilant of any surges or shorts.

Calibrate Analog Components

Always refer to the preventative maintenance schedule for any analog input device. Analog inputs need to be cleaned regularly and calibrated as accurately as possible.

Take EMI into consideration

EMI (electromagnetic interference) is known to cause horrible issues for PLCs without clearly indicating what the specific issue is or how to go about fixing it. To remain ahead of the game, many perform an audit of the local wiring to pinpoint potential EMI sources before they interfere with the operation of your PLC. Lower-level components and high-current wires often interfere with each other, which wiring designs must take into consideration.

Additional PLC Maintenance Tips

By creating a PLC maintenance checklist and adhering to it strictly, operating errors can likely be avoided. The space between the PLC and the machine it’s controlling should be minimal.

MRO Electric and Supply has new and refurbished Modicon PLC parts available here. We also offer repair pricing. For more information, please call 800-691-8511 or email sales@mroelectric.com.