Process control systems (PCS), sometimes referred to as industrial control systems (ICS), include monitoring and troubleshooting equipment. The equipment is mounted along the production line and is used to provide information on the smooth running of the manufacturing process.

PCS systems can be simple, with a single sensor, often called a primary translator, along with a controller that processes the input and a receiver that processes the output. Or they can be complex, widely found in industries such as chemical processing, paper manufacturing, electricity production, oil and gas processing.

Most processes nowadays use DCS (Distributed Control Systems) and/or PLCs (Programmable Automation Controllers). Currently the functionalities of these control systems have merged, the PLCs have functionalities that until now were only found in DCSs, and the DCSs are capable of performing many functions that until now only the PLCs could fulfill.

PLCs have emerged as replacements of relay control systems, being used to control discrete processes and independent equipment. It is necessary to integrate them with other equipment, such as HMI (Human-machine interfaces).

DCSs, on the other hand, have emerged to replace PID controllers and are used in continuous production processes, especially for those that require advanced control measures. These systems are marketed with dedicated applications for programming and monitoring.

Even though PLCs are less expensive and can achieve almost all the features of a DCS, there are six major differences between them, as shown in the table below.




Response time

Faster, being ideal for real-time control;


Information processing takes longer, not recommended for security systems;



 It can operate with several thousand I/O;


More scalable, can operate with a large number of thousands of I/O, being perfect for the processes that extend over a large geographical area;




Does not support I/O with errors tolerance;


Supports redundancy, I/O are error tolerant;




Solution for simple processes, such as paper production;


They are the perfect solution for complex processes, such as oil and gas production, water treatment and chemical processing, processes that require advanced control;


Frequency of process change


Used for discrete processes, which do not change often;


For complex processes, which require continuous adjustment and analysis of large data blocks, it is necessary to integrate DCSs;




PLC developers provide support services through the network of integrative system partners;


DCS developers ask for their commitment to provide the integration and implementation service


Table 1. Major differences between PLC and DCS

 In order to choose the optimal solution for the own process, the differences highlighted in the table above must be taken into account and the cost and performance of each equipment must be balanced.