PLC vs. Microcontroller

The onset of the third industrial revolution in the latter half of the 20^th century set off a new wave of innovation on the global industrial stage. ‘Automation’ was the keyword that drove R&D during this period. A whole new fleet of controls technologies was developed that enabled the transition from primarily manual-based to automated industrial setups. At the forefront of this technological change were Programmable Logic Controllers (PLC). These devices entered the market in the 1970s and were quickly adopted by industrialists across the board. In the present age, PLCs are ubiquitous in almost every industry and carry massive scope for further improvements in the future.

Branching out of this is another rapidly growing tech, the Microcontroller (sometimes abbreviated as MC). Due to its unique qualities, it has become popular in the DIY and product design markets, where embedded control systems are the ideal choice. People who build small-scale machinery (like 3D printers, CNC routers, smart home concepts, etc.) prefer to work with microcontrollers. However, it is not as simple as a ‘micro’ controller for ‘small’ machines and PLCs for bigger machines, as it may seem to be. These are very different technologies whose application areas happen to overlap quite a bit.  

Due to this overlap, there is some decision-making that goes into choosing a controller for your specific application. This article presents a comprehensive comparison of PLCs and Microcontrollers to help you in making an informed decision.  

What are PLCs & Microcontrollers? 

Before diving into the details, however, let us give a brief refresher on both controllers to get the juices flowing.  

PLC

PLCs, as discussed above, are industrial-grade controllers prevalent in many businesses around the world. An easy analogy to understand them would be a personal computer (PC) that we all are familiar with. PLCs are basically specialized computers designed for an industrial setting. It has similar components, a user interface, and the same concept of hardware/software. The composition of a normal PLC is as follows.

• Central Processing Unit (CPU): Much like a PC, PLCs have a data processing unit that is the brains of the system. The decision-making and process control are performed by this unit.  
• Memory: The CPU needs a place to store and retrieve data from somewhere to execute its program. Non-volatile RAMs are the prime choice of PLC OEMs.  
• I/O: PLCs communicate with external devices. This connection with these devices is via an I/O (Input/Output) interface. 
• Operating System + Software: As with computers, there is an OS that is an intuitive interface between the user and the machine code. Software is used for functional requirements like programming, troubleshooting, setting up, etc. 
• Power Supply: This is a self-explanatory heading, the power supply provides energy to the whole setup. Usually, power supplies integrate electronic components to change input power to the voltage/current requirements of the PLC.  

Microcontrollers

Microcontrollers have the same architecture as a PLC. There is a data processing unit, a local memory, I/O, and a power supply to energize its circuitry. How is it different then, you may ask? Physically, a microcontroller is a Printed Circuit Board (PCB), most often in the form of a small chip. This PCB houses all the other components outlined above. PLCs are bigger with everything as a separate unit. The Arduino is the perfect example of an MC. In fact, you may be reading this on your smartphone, which houses multiple microcontroller chips inside of it. A small PLC, on the other hand, cannot fit inside your pocket. 

PLCs vs. Microcontrollers: A Comparative Analysis

Apart from the physical size, there are several other subtler differences between PLCs and MCs that we will now explore one by one.

Computational Capability

First things first! A discussion about computers is incomplete without processing power. PLCs and microcontrollers are both hard real-time systems designed for near-instantaneous control. You may have already guessed that PLCs are superior in terms of computational capabilities. They house stronger data processing units, often multiple-cored stacks, making them capable of dealing with highly demanding industrial tasks.

Generally, they have a scan time in the range of 10-50ms, which is really how low it gets for industrial applications. Microcontrollers are comparatively limited in terms of data handling. They may have comparable technical specifications but cannot handle the same volume of data. MCs are good at performing one (or a few) control task at a time but when it comes to multivariable problems, they max out very quickly.

I/O

Input and output interfaces of a controller are crucial elements in the control system. Industrial PLCs come with an extensive variety of I/O ports. The control engineer can easily integrate digital or analog I/O signals, over a range of currents/voltages, and install safety measures that are supported by the I/O itself. The modular design of PLCs also allows the number of I/O ports to be increased to hundreds by simply retrofitting additional I/O modules. 

Microcontrollers have their own I/O as well but are not as broad as PLCs. The number of ports is limited and the designer may not enjoy as much convenience in terms of incorporating analog signals over different voltage/current ranges.  There is code that can be used to filter and convert input/output signals but it increases cost and is still limited on many fronts.

Interconnectivity

At any given moment, controllers are receiving input signals, converting them to other forms, processing data for decision-making, and sending out signals to actuators. This entire loop is only possible if efficient communication is present within the system. Thus, interconnectivity plays a huge role in controllers. In PLCs, there are a number of built-in ports for communication media like Ethernet, USB, RS-232, etc. Through these, the PLC can communicate with other devices via a wide range of industry-standard communication protocols (EtherNet/IP, Modus, Profibus, etc.).

Microcontrollers, due to their small size, do not accommodate as many ports, limiting their utility in a larger control environment. They are also designed to support a certain class of data sharing protocols, making them best-suited for specific applications but a bad choice for anything else. Within their design sphere, they can sometimes process data quicker than PLCs, though.

Controller Programming 

A big chunk of the cost for a control system is the programmer’s salary. Thus it makes sense to know the differences between PLC and Microcontroller programming before finalizing which one to buy.  The PLC industry has gone through a series of standardizations and regulations over the past few decades, which has taken a solid shape by now. The IEC 61131-3:2013 standard pinpoints numerous aspects of PLC design, presenting manufacturers with a clear guideline of what they need to do. 

This has had a positive effect on the development of PLC programming environments. Most OEMs now follow a set of rules when it comes to devising syntax for their PLCs, which often follows the infamous Ladder Logic.  This standardization process means that a single programmer can work with different PLCs without considerable effort.

Microcontrollers are still new and have not yet gone through rigorous standardization. However, their programming stems from commonly used object-oriented languages like C, JavaScript, and even Python. Programmers need to develop a sense of dealing with assembly language and debugging but the grassroots-level syntax is similar. We would also like to add a short paragraph on how programming environments differ. In PLCs, this can be different for each OEM and users need to spend some time to get acquainted with the interface. For MCs, the environment is different for each product too but all of them are quite similar to daily-use software (so it is like using different versions of Microsoft Excel, for example).  

Data Security

As we move into Industry 4.0, there is an increasing risk of cyberattacks as layers of interconnectivity between devices increase. Control engineers have taken up the challenge and are developing technologies with better security measures. The sheer size of the PLC industry again plays a role in this changing dynamic. There is rigorous funding to back the development of PLCs that are less prone to getting infiltrated by cyber threats. Standardized security protocols are in place for OEMs to follow. Microcontrollers are not that different either as data security is mainly at the software level. What they might lack is the backing of a centralized, directed effort due to their open-source nature. Everyone chips in their two cents which is good for specific cases rather than universal control environments.

Working Environment

Industrial environments are rough and contaminated. Production machinery creates vibration, heat, chemical pollutants, corrosive elements, vapors, electrical noise, etc. Controllers need to be robust to survive in such environments and perform with minimal downtime.  

PLCs are designed with such conditions in mind and are generally up to the task. They often come in metal cabinets, damped from vibrations and protected from the environment. They can be further ruggedized for extreme environments by the OEM.  Microcontrollers normally come unprotected. This is not a flaw, it is just how the product’s identity has developed. If the user wants more protection, they can get enclosures and other supplementary protection. However, it requires customized designing and manufacturing, which is both time-consuming and costly.   

OEM Support

The level of support provided by the equipment manufacturer differs a lot between PLCs and MCs. PLCs, as highlighted above, are the product of a well-developed, standardized industry. The OEMs operating in it are established enterprises that specialize in providing industrial solutions. Such companies have dedicated customer support departments that collaborated with (potential) customers to figure out what is best for them, help them in installation, and offer the entire gamut of after-sales service.  

PLC buyers can also get official training from the seller for their specific PLC model, tailored for their specific application.  Moreover, PLC companies have huge R&D setups that closely monitor the overall performance of their products and work on improved versions. Due to their clientele being so widespread, they also ensure that subsequent generations are compatible with current ones.

Microcontroller users do not enjoy as many facilities. In most cases, there is no additional support from OEMs except for the standard user manual and basic training. Continuity in successive models is also not fully ensured and users of new generation models might find bugs in code that previously worked well. There is, however, a plethora of open-source material available to MC users. They can train themselves and discuss issues on online forums as much as they want, something which is not as easily accessible to PLC customers. 

Size

PLCs are considerably larger than Microcontrollers. The size of a PLC mainly depends on the buyer as they may choose to purchase additional modules to enhance their PLC’s functionality or capability. The basic PLC unit, however, is still much bigger than an MC chipboard as it is a standalone unit on its own. Microcontrollers, on the other hand, are portable, handheld devices. Users can easily manage them and put them wherever they want on their build. This brings us to our next point: mounting. 

Mounting

The physical location of the PLC matters in the spatial layout of a control system. A microcontroller, owing to its small size, can be fixed almost anywhere. They are lightweight so they can be placed on the machinery itself without damaging it. As for PLCs, their size warrants a bit more planning in deciding their physical placement in a plant. PLC cabinets are often placed at dedicated spots on shop floors or are fixed on walls/heavy machinery for easy access. The place also has to be accessible by wires and clear of pathways, further increasing the hassle. 

Cost

At the end of the day, it all boils down to how much money you have to spend. PLCs, naturally, cost a lot more than Microcontrollers due to their bigger size and broader application range. Depending on the industry and investor, an expensive PLC with precise control capability and high-quality components may be chosen for better performance. On the contrary, a comparatively rudimentary industry may be well-off with a cheaper, less precise version as the requirement is not that high.  

For Microcontrollers, the product development is still in its initial stages and the market is much more dynamic. There are very cheap boards that you can buy for your child’s robotics class, there are also high-end MCs that have been put to use in quite impressive DIY builds. In conclusion, it is the same as any market. The cost goes up with quality and requirement, and vice versa. In general, PLCs cost more than MCs.  

Final Thoughts

We hope that the information given above was helpful and you now feel more confident about the topic. The controls industry is not static in any way, it keeps on evolving with new and better products introduced frequently. It is easy to get bogged down in the details and get confused. We tried to convey the timeless basics so you can make better decisions. If you have any more queries or are looking to buy a controller, feel free to contact our technical staff who will be more than happy to assist you. For more information or to discuss which equipment might be best for your application, please visit our website here, or contact us at [email protected] or 1-919-535-3180. 

This entry was posted on December 13th, 2021 and is filed under Uncategorized. Both comments and pings are currently closed.