what is Programmable Logic Controller(PLC)?

A programmable logic controller (PLC) is a microcomputer which is designed to control processes and events in an industrial environment-that is,to take over the job previously done with relay logic controllers.so we can say PLC is the replacement of relay logic controller.
PLC  has some advantages-
Programmable Logic Controller (PLC)  is suitable for rugged design harsh industrial environments against   high temperature variations, dust, and vibrations
it has    Industry standard I/O interfaces;
capable of communicating with other PLCs, computers and intelligent devices.
Industry standard programming languages; easily learned and  understood. Programming is primarily concerned with logic, timing, counting and switching operations.
 Field programmable.
 Reduces hard wiring and wiring cost.                                                                                                            Monitoring, error checking and diagnostics capability.
Competitive in both cost and space requirements. 

Basic Components:
 PLC is essentially a microcomputer, tailored specifically for certain  control tasks.
 Hardware: consists of the actual device technology, i.e. the PCBs,  integrated modules, wires, battery, housing etc.
Firmware: is the software part, known as executive software, that   is permanently installed and supplied by the the PLC  manufacturer. Programs are usually stored in ROM or EPROM.
Software:is is the user program.user program usually stored in the RAM.
 What is Firmware? 
 PLC hardware does not differ significantly from computers. What  makes the PLC special is the executive software. It is the internal  program, provided by the manufacturer,which executes the user’s program.       The executive software determines                                                                 
-  what functions are available to the user’s program,
-  how the program is solved,                                                                      
-  how the I/O is serviced,
-  what the PLC does during power up and down and fault conditions.
                                                                                                                                                       Multitasking Capability
Some PLCs are capable of executing multiple tasks with a single processor.user  program assigns I/O for each task separately.
Multitasking may take several forms:
Time driven - it is possible to configure the processor to run each task on periodic time intervals.
Event driven or interrupt driven-user defines a particular event,such as input changing state or an output turning off,that causes each tasks to run.



Considerations in Choosing PLC :
1.Number and Types of input & output points required
2.Size and type of memory required
3.Speed and power required of CPU and instruction set
4.Manufacturer’s support and backup
PLCs basic hardware are-
power supply,memory,Central processing unit(CPU)/logic solver,I/O interface ,programming section.
Memory:The memory function of CPU stores program and data that's the CPU need to perform various operations.The memory is to organized into several sections-

• Executive memory
• Scratch pad
• Processor file

Central processing unit(CPU):
CPU execute a program stored in executive the memory is set by the manufacturer.It organize all control activities by receiving inputs,performing logical decisions according to the program,and control the output.CPU does not operate I/O directly,its works with the I/O image stored in the I/O image memory.The I/O interface is responsible for transferring the image outputs to the I/O system.A "watchdog " timer is provided to time the CPU to executed the user's program.

the HVAC System,an integral part of building construction.

Now a days HVAC system is an integral part in building construction field.HAVC means heating, ventilation and air conditioning.
the ancient Romans had remarkably good radiant heating in some buildings,which was achieved by warming air and then circulating it in hollow floors and walls.In the dry climate of the middle east,people hung wet mats in front of open doorways and achieved a  crude form of evaporative air cooling.In Europe,Leonardo da Vinci designed a large evaporative cooler.
The development of HVAC was begun scarcely 100 years ago.Central heating system was developed in the nineteenth century,and summer air conditioning using mechanical refrigeration has grown into a major industry only in the last 60 years.A typical person in modern society may spend up to 90% of each day indoors.It is not surprising,therefore,that providing a healthy,comfortable indoor environment has become a major factor in our economy.
Air conditioning:
many of the peoples air conditioning simply means "the cooling of air".for engineering purpose this definition is neither sufficiently useful no accurate.the real definition is-
Air conditioning is the process for treating air in an internal environment to establish and maintain required standards of temperature,humidity,cleanliness,and motion.
Sound control can be considered an auxiliary function of air conditioning system.even though the system itself may be the cause of the problem.the air conditioning equipment can produce excessive noise,requiring additional sound attenuating devices as part of the equipment.
The definition of air conditioning given hare is not meant to imply that every HVAC system regulates all of the conditions described.A hot water or steam heating system only control air temperature,and only during the heating season.A warm air system also control temperature in winter only.by adding humidifier we can also control humidity.
Air conditioning system used for newer commercial and industrial buildings and luxury apartment houses usually provide year-round control of most or all of the air conditions described.For this reason,it is becoming increasingly popular to call complete HVAC systems environmental control systems.
Components: most heating and cooling system has following basis components-

• A heating source
• A cooling source
• A distribution system
• Equipment for moving air or water
• devices for transferring heat between the fluid and the room

the development of an HVAC system for a building consists of a number of steps.these are- 

• design 
• installation
• operation &regular maintenance
• service

If anyone want to learn about HVAC ,the most important thing is to locate a proposed building and follow the HVAC system development through planning ,installation,and operation.This experience will help him a lot to get a clear concept about HVAC beside study.

Refrigerants ,Ozone depletion and Global warming.

 what is refrigerant?
A refrigerant is any body or substance,which acts as a cooling agent by absorbing heat from another body and substance.theoretically, any reasonably  volatile substance which is liquid at the temperature desired in the evaporator can be used as a refrigerant,but in practice the choice is limited by factors such as toxicity,cos ,flammability,chemical stability etc.
there are two types of refrigerants,primary refrigerant & secondary refrigerant.

primary refrigerant:A primary refrigerant is one ,which is used in a recirculating cycle and is accompanied a change in state.during cyclic process it undergoes compression,condensation,expansion and evaporation.

secondary refrigerant: A secondary refigerant is one,which is used as heat transfer medium without a change of state but with a change in temperature.

many refrigerants have been used over the years and some of them have become obsolete and since replaced by newer refrigerants.some currently popular refrigerants are being phased out due to their damaging effect on ozone layer.conventional refrigerants are four types-
1.Inorganic 2.Azeotropes 3.Halocarbon 4.Hydrocarbon.
Ozone Depletion and Global Warming:
among these four refrigerant groups,some of the rfrigerants in the Halocarbon family have lost favour becouse of their negative impect on environmental issues.
Helocarbon refigerants contain one or more of the three halogens-chlorine,fluorine and bromine.these refrigerants are obtained by replacing one or more hydrogen atoms in a hydrocaron molecule.because of their great stability,fully halogenated compounds,such as chloflurocarbons(CFCs) persist in the atmosphere for many years and eventually diffuse into the atmosphere.the molecules of CFCs ,such as R11 and R12,contain only carbon and halogens contains contain chlorine and fluorine.
Once in the uper atmosphere,the CFC molecules break down releasing chlorine,which destroys ozone and causes Ozone Depletion.

In the lower atmosphere ,the CFC molecules absorb infrared radiation,which may contribute to the worming of the earth,this is called Global Warming.Substitution of a hudrogen atom by  one or more of the halogens in a CFC molecules greatly reduces its  lifelime in atmosphere and consequently its negative impect.These compounds are reffered to as hydrochlofluorocarbons(HCFCs).
So the ozone depleting refrgerants will be phased out as per decision of the Montreal protocol,an international treaty.

what is mechatronics?

mechatronics is the synergistic combination of  precision mechanical engineering,electronic control and system thinking in the design of products and manufacturing process.
we can also say, mechatronics is a methodology used for the optimal design of electromechanical products.

the portmanteau mechatronics  was first coined by Mr Tetsuro Mori,a senior engineer of the japanese companyYaskawa.in1969.

mechatronics constituents:there are three basic mechatronics constituences.they are-

1. Electronic Engineering
2. Mechanical Engineering
3. software Engineering

Mechatronics key elements: there are some mechatronics key eklements-

• modeling and simulation
• automatic control
• opimization
• mechanical systems
• electrical systems
• computer systems
• actuators
• sensors

What is modeling and simulation?
Modeling: modeling is the process of representing the behaviour   of real system by a collection of mathematical equation and logic.
Simulation: simulation is the process of solving the model and is performed on computer.
simulation process has three basic steps-

1. Initialization
2. Iteration
3. termination

what is optimization?
In mechatronics optimization is primarily used to establish   the optimal system configuration.its solves the problem of distributing limiting resources throughout a system such that the pre-specified aspects of its behaviour is satisfied.
automation in production system:
it as technology concerned with the application of mechanical ,electronic and computer based systems to operate  and control production.
production system is the collection of people,equipment,an procedures organized to accomplish the manufacturing activities of a company.it can be divided into two categories-

• fcilities
• manufacturing support system

references:
M.B. Histand & D.G. Alciatore,Introduction to mechatronics & measurement systems,McGraw-Hill,Inc.
S. Centinkunt,mechatrinics,J. Wiley &Sons,Inc.
C.T. Kilian,Modern Control Techology,Thomson Delmar Learning.

what is modern control system ?

a control system is an interconnection of  components forming a system configuration that will provide a desired system response.
primary reasons: power amplification,remote control,convenience of input form,compensation for disturbances.

important outcomes:1. increased productivity and lower product cost 2.better and more uniform quality of product 3.greater safety for operating personnel.

classifications:
open loop system: output has no control on control action.
closed loop system: maintains a prescribed relationship between the output & some reference input by comparing them and using the difference as a means of control.
servomechanism: a feedback control system to control motion.
process control system: a process control system where one or more process variables such as temperature,flow,fluid leveletc are controlled.
batch process: is a sequence of timed operations executed on the product being manufactured.
continuous process:one or more operations are being performed as the product is being passed through a process.


controllers:
1.continuous controllers
2.discontinuous controllers

continuous controller: P controller,I controller,PD controller,PI controller,PID controller.

discontinuous: two-position,three-position, multiposition controller.