Saturday, September 25, 2021

Process Control

Before going to details of Process control and Automation, Lets understand its basic first. The approach to identify the actual status of ongoing processes at any instance of time, re-analyse the acquired data in accordance with preset rule and guiding principle and consequently carrying out the operation of control element is called Process control.

Basic block diagram for Process control

In controlling all the processes, the above mentioned activities may be undertaken by human being only, or by man-machine collaboration, or even by machine only. However, Here we are discussing about the controls that can be shifted gradually to machines to minimise the efforts of human being. So let us concentrate on that only.

What do you mean by automation?? Got the idea but not able to define !! In a simple way, Automation can be defined as the

Definition of Automation:

Automation is basically the process to delegate the jobs performed by human beings to a machine with an aim to achieve :

  • More efficiency

  • Excellence in quality of the manufactured goods

  • Minimise the wastage of power and resources

  • Better safety

and many more.

Automation/Process Control History:

Progressive growth of the Process control system

The various method adopted in human history for process control and automation are as follows:

1.   Manual Control :

In such condition, all the jobs of process control/automation are carried out by operators. This system has many disadvantages. The most commonly occurring disadvantage is “Human-error”. This also further affects the quality of the output we are getting.

            There are a lot of other limits too if we further raise our scale and go in mass-productivity. If we go for a better output quality, then we have to limit this human-error by increase in human strength which will further result in increase of manufacturing price of the item. The more it will be human strength, the less will be the precision and so will come the safety issues. Furthermore, the consumption of raw material as well as the power will also be more, as it directly relates with the precision of human proficiency.

2.   Logic control (Hard-wired) :

Mankind gradually evolved with days started his first attempt in the direction of automation. This was the ‘Era of Hard-wired logic controls’. At that time the partial automation was achieved with the help of Electro- mechanical/magnetic elements (Relay/contactor/timer/counter). This method was very popular for a long time and used on vast scale, it, too, was having many limits attached with it :

  • massive cabling (and a complex one)
  • Less reliable and prone to failure.
  • No redundancy. Even one element’s failure dumps the whole system.

3.   Control with Electronics :

As the Electronic world started to work reliably, the Flip-flops and Logic-gates (AND, OR, NOT and its combinations) replaced the Hard-wired control elements in the circuitry. Very soon, Electronics replaced the old aged electro-mechanical and Capacitor based timers too. This replacement to electronic elements brought us the following advantages:

  • Less bulky. Saved a lot of space.
  • Increase in power efficiency. Low power consumption.
  • More reliable. Failure of electronic component was much less in comparison.

Though this electronic change brought more reliability in process control, there was still no flexibility of changing the process control structure with requirements.

4.   PLC based Control :

PLC stands for Programmable Logic Control. PLCs brought a revolutionary change in the process control method, as it was fully flexible and was programmable as per needs. The golden era in PLC based controls started with the arrival of microcontroller and micro-processor (the name surely rings a bell, isn’t it). These PLC almost removed the complex cabling of control elements as the process control could now be achieved by programming only. There is no need to change the circuitry/control elements again and again as simply a change of program can now give us the desired control.

We can see a PLC control almost everywhere ranging from a simple toy to a vast industrial controls.

In our next post, we will go through PLCs in detail. Till then, take care and keep learning.

Sahil Mishra
Sahil is a BTech in Marine Electrical. He is also a Reliability Analyst and has specializations in Russian Control Systems, Machinery Control System and Automated Power Management. He has work experience of 18 years. He is an Author, Editor and Partner at Electricalfundablog.
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