DIFFERENCES BETWEEN PLCs AND MICROCONTROLLERS:

Gone are the days when microcontrollers were the most popular all over. Now PLC has taken charge of the industrial sector world wide and across Pakistan.

All the industries in Pakistan are now using PLC systems in different ways some of the salient features of PLCs are:

PLCs are robust

PLCs are reliable

PLC Architecture is interchangeable

Integration with multiple communication protocols

Extendable I / Os

Availability for redundant architectures

Easy to communicate with HMIs

Easy to maintain

Easy to use Safety PLCs are available for hazardous processes.

While microcontrollers have some drawbacks:

Microcontrollers are not designed to withstand extreme conditions such as PLCs with the roughness and unique ability. This does not make them ready for industrial applications.

Microcontrollers are considered to be of vital importance in industrial applications by the university students a perception which they created during their academic years. However the use of microcontrollers is very limited. I have occasionally seen the role of them in industries. On the other hand PLCs are the main building block of automation and are widely used across whole country in various different industries.

PLCs and microcontrollers are some of the most misunderstood systems. That misconception comes from the fact that most people try to understand them only from a traditional software engineering perspective. They think that since microcontrollers can be programmed in C or C++ (traditional programming languages for traditional software development), then they must behave like traditional software. In reality, they are more like hardware systems, and have issues that are usually faced in hardware design. Since microcontrollers behave like software, and PLCs are programmable devices like microcontrollers, they too must behave like software.

Today we will discuss the brief comparison between these two technologies and try to cater the questions often arises in student’s mind.

Programmable Logic Controller (PLC) defined by NEMA as a digitally operating electronic apparatus that uses a programmable memory for internal storage of instructions for implementing specific functions such as Logic, Sequencing, Timing, Counting And Arithmetic Through Digital Or Analog Input / Output modules.

A PLC system could range from a stand-alone system that can take 10 digital inputs and 10 digital outputs and a few analog inputs and outputs, to a complete DCS that controls an entire plant or field, with tens or hundreds of different modules connected over long distances, multiple processing units and redundant systems.

At the heart of the PLC is ease of use, but not in the manner that one might think. Its ease of use is in terms of deployment and maintenance. Couple that with reliability and scalability and a system that is almost unbeatable.

Pros:

·         Large capacity - The PLC nowadays have a capacity of 2000+ I/Os that is analog and digital combined. This is maintained through a central engineering station for ease of control.

·         Modular Design - The PLC capacity and design can easily modified to suite customer need post implementation stage. This is not feasible with relays or microcontroller based solutions.

·         Distributed architecture - For large application a distributed system can be implement with communication between various PLC using protocols like Modbus, Ethernet and profibus etc.

·         Industrial Grade - PLCs are designed with tolerance to withstand various hazardous condition for Industries such as Electromagnetic interference, high temperature, power fluctuation etc.

·         Safety - PLCs manufacturers also provide safety features such are SIL certification as per customer requirement for Protection/Emergency Shutdown System.

·         Utility - PLCs can interface with a large no of drives and actuators ranging from analog and digital to special type such as speed measurement and RTD/thermocouples etc. These can be done easily by changing I/Os modules and configuring them.

·         Easy Maintenance and Spares - Due to modular design the trouble shooting is easier and the no of spares requirement is reduced and easily manageable.

Microcontroller is a microprocessor with internal input and output and memory i.e. RAM, ROM, PORTS. It needs surrounding circuitry in order to function. It has little or no real-word signal level compatibility (cannot connect it to a thermocouple or a motor directly). It is typically the central building block in a system that is built up along with other components. 

Pros:

·         In case of Microcontroller the programming is somewhat tedious because of machine language.

·         A microcontroller is also a logic controller but used in dedicated systems which are programmed once and for all, the program for which will not be accessed by the user, and whose program will not need to be altered frequently.

·         Microcontrollers Developed for Dedicated equipment.

·         With a microcontroller, you may have to design your own signal interfacing.