The word
‘Automation’ is derived from Greek words “Auto” (self) and “Matos” (moving).
Automation therefore is the mechanism for systems that “move by it-self”.
However, apart from this original sense of the word, automated systems also
achieve significantly superior performance than what is possible with manual
systems, in terms of power, precision and speed of operation.
Definition: Automation is a set of technologies
that results in operation of machines and systems without significant human
intervention and achieves performance superior to manual operation.
Industry
:- In a general sense the term “Industry” is defined as
follows.
Definition: Systematic Economic Activity that could be related to
Manufacture/Service/ Trade.
Control :- It is perhaps correct
to expect that the learner for this course has already been exposed to a course
on Control Systems, which is typically introduced in the final or pre-final
year of an undergraduate course in Engineering in India. The word control is
therefore expected to be familiar and defined as under.
Definition: Control is a set of technologies that achieves desired patterns of
variations of operational parameters and sequences for machines and systems by
providing the input signals necessary
Open and closed loop:- All the
elements constituting the measurement and control of a single variable are
called a control loop. Control
that uses a measured signal, feeds the signal back and compares it to a set
point, calculates and sends a return signal to make a correction, is called closed loop control. If the
controller does not incorporate feedback to make a correction then it is open loop. Timers and sequence
controllers using logic, such as those on an elevator, are open loop.
Feedback control
:- Feedback control is accomplished with a controller. To function properly, a controller
must provide correction in a manner that maintains stability. The theoretical
basis of feedback control is control theory, which
also covers servomechanisms, which
are often part of an automated system.
Maintaining stability is a
principal objective of control theory. Stability means that the system should
not oscillate excessively around the set point or get into a situation where it
shuts down or runs away.
As an example of feedback
control, consider a steam coil air heater in which a temperature sensor
measures the temperature of the heated air, which is the measured variable.
This signal is constantly "fed back" to the controller, which
compares it to the desired setting (set point). The controller calculates the
difference (error), then calculates a correction and sends the correction
signal to adjust the air pressure to a diaphragm that moves a positioner on the
steam valve, opening or closing it by the calculated amount.
The complexities of this
are that the quantities involved are all of different physical types; the
temperature sensor signal may be electrical or pressure from an enclosed fluid,
the controller may employ pneumatic, hydraulic, mechanical or electronic techniques
to sense the error and send a signal to adjust the air pressure that moves the
valve.
The first controllers used analog methods
to perform their calculations. Analog methods were also used in solving
differential equations of control theory. The electronic analog computer was
developed to solve control type problems and electronic analog controllers were
also developed. Analog computers were displaced by digital computers when they
became widely available. Common applications of feedback control are control of
temperature, pressure, flow, and speed.
. . .
No comments:
Post a Comment