Chapter 1
Simplification of engineering and precise control of
manufacturing process can result in significant cost savings. The most cost-effective way, which can pay
big dividends in the long run, is flexible automation; a planned approach
towards integrated control systems. It
requires a conscious effort on the part of plant managers to identify areas
where automation can result in better deployment/utilization of human resources
and savings in man-hours, down time.
Automation need not be high ended and too sophisticated; it is the
phased, step-by-step effort to automate, employing control systems tailored to
one’s specific requirements that achieves the most attractive results. That is where Industrial electronics has been
a breakthrough in the field of automation and control techniques.
ROLE OF ELECTRONICS IN AUTOMATION
A constant demand for better and more efficient
manufacturing and process machinery has led to the requirement for higher
quality and
reliability in control techniques.
With the availability of intelligent, compact solid state electronic
devices, it has been possible to provide control systems that can reduce
maintenance, down time and improve productivity to a great extend. By installing efficient and user friendly
industrial electronics systems for manufacturing machinery or processors, one
can obtain a precise, reliable and prolific means for generating quality
products.
Considering the varied demand and increasing
competition, one has to provide for flexible manufacturing process. One of the latest techniques in solid state
controls that offers flexible and efficient operation to the user is
“PROGRAMMABLE CONTROLLERS”. The basic
idea behind these programmable controllers was to provide means to eliminate
high cost associated with inflexible, conventional relay controlled
systems. Programmable controllers offer
a system with computer flexibility:
1.
Suited to withstand the industrial environment
2.
Has simplicity of operation
3.
Maintenance by plant technicians and
4.
Reduce machine down time and provide expandability for future.
DEFINATION
OF PLC
A Programmable controller is a solid state user
programmable control system with functions to control logic, sequencing,
timing, arithmetic data manipulation and counting capabilities. It can be viewed as an industrial computer
that has a central
processor unit, memory, input output interface and a
programming device. The central
processing unit provides the intelligence of the controller. It accepts data, status information from
various sensing devices like limit switches, proximity switches, executes the
user
control program store in the memory and gives appropriate
output commands to devices like solenoid valves, switches etc.
Input output interface is the communication link between
field devices and the controllers; field devices are wired to the I/O
interfaces. Through these interfaces the
processor can sense and measure physical quantities regarding a machine or
process, such as, proximity, position, motion, level, temperature, pressure,
etc. Based on status sensed, the CPU
issues command to output devices such as valves, motors, alarms, etc.
Programmer unit provides the man machine interface. It is used to enter the application program,
which often uses a simple user-friendly logic.
BENEFITS OF PROGRAMMABLE CONTROLLERS
1. Programmable controllers are
made of solid state components and hence provide high reliability.
2. They are flexible and
changes in sequence of operation can easily be incorporated due to
programmability. They may be modular in
nature and thus expandability and easy installation is possible.
3. Use of PLC results in
appreciable savings in Hardware and wiring cost.
4. They are compact and occupy
less space.
5. Eliminate hardware items
like Timers, counters
and Auxiliary relays.
The presence for timers and counters has easy accessibility.
6. PLC can control a variety of
devices and eliminates the need for customized controls.
7. Easy diagnostic facilities
are provided as a part of the system.
Diagnosis of the external systems also becomes very simple. Thus easy service/maintenance.
8. Programming devices provide
operator friendly interface with the machine. Being an outcome of the latest
art of electronics technology, Programmable controllers provide higher level of
performance with computers is possible.
Useful management data can be obtained and maintained.
9. It has total protections
against obsolescence and has wide scope for up gradation.
Chapter 2
PLC ARCHITECTURE
PLCs contain three basic sections:
1.
Central processing unit (CPU).
2. Memory: EPROM, RAM, and so on.
3. Input/output section for communication with
peripherals (ADC, DAC).
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