Controls - The Building Blocks to Automation

By: Thomas Yoon

As man learns to make machines that no longer rely on animal
or human power, he finds that he has to develop some means to
manage and control them. Powerful machines let loosed by
themselves will create havoc and destruction.

Control systems have been developed for machines or processes
so as to reduce the chances of failure and to provide the
required results.

Basically, there are open loop control systems and close loop
control systems.

Open loop systems are those where the controller action is not
related to the final result. This means that there is no
feedback to the controller to adjust the control action. A
simple example is when you fill up a tank using a garden hose.
As long as the tap is opened, the water will flow. The height
of the water in the tank will not make the tap close.

However, when you see the tank becoming full and decide to
close the tap, you are adding the element of feedback to the

It then becomes a closed loop. But it is a human
controlled closed loop.

Closed loop systems use feedback from the final result to
adjust the control action accordingly.

But how would you like to stand in one position, watch the
process going on and operate valves, or switches according to
the conditions you want? This is very tiring, isn't it?

Moreover, human beings are prone to fatigue, boredom, and
misjudgment. Manual control works very well only if the speed
of the response is very slow, and the result is not very
critical or important. Human controlled systems can become
very unreliable.

Machines are made to replace humans in most control systems

The basic feature of any control system consists of 4 elements.
These are the measuring element, the controlling element, the
set value, and the correcting element.

The measuring element provides a means of detection/measurement
of the conditions required. This is the "eyes" or "ears" (or
other senses) of the system.

The controlling element is the place where all the decisions on
what actions to take are being made. It can be considered the
"brains" of the system. It must make decisions based on certain
guidelines or values required. The set values are inputted into
the system by humans.

The correcting element is where the correction to the process
is done. It can be considered like the "hands" or "feet" of the
system. It must take certain physical actions to bring the
processes back to the set value.

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