Programmable Logic Controller

We use a PLC to operate our bagging system which has 4 inputs including magnetic switches, photo-electric sensors and a proximity sensor. The machine has 7 air valves which control 4 air cylinders (extend/retract) which operate valves and other mechanisms. Our controller is programmed on our PC and with one click, is dumped to the controller board where the inputs and outputs are connected. Power-up the controller and the system runs itself. We investigated dozens of controllers and for too many reasons to list, chose the SPLATPC controller. It is fabulous!!. Check it out at <http://www.splatco.com>. Please reply to this if it was helpful Thanks, MAX

Because you can program it what to do and it is an independent control that doesn't depend on an outside computer that is prone to crashing, such as a Windows based computer, etc. It is its own little logic center and retains its programming independent of external systems. So, if you utilised a system that depended on a PC to control something with a software application, and that PC locked up or lost the hard drive or just received a virus, you are in trouble. But the PLC takes programming you put in with a notebook, then you disconnect the notebook, the PLC retains the programming, it applies rule sets you give it, and uses those rule sets to control something. And it has multi channels. Think of it as a very robust computer that actually works for simple rule set tasks, not like the one I am using to type the message !

George

My Dear Mani i am just reproducing the write up from web site http://www.plcs.net you will find host of basic inofmation on PLCs at this site hope it would be of use to you

A PLC (i.e. Programmable Logic Controller) is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software, that gives the desired results.

PLCs are used in many "real world" applications. If there is industry present, chances are good that there is a plc present. If you are involved in machining, packaging, material handling, automated assembly or countless other industries you are probably already using them. If you are not, you are wasting money and time. Almost any application that needs some type of electrical control has a need for a plc.

For example, let's assume that when a switch turns on we want to turn a solenoid on for 5 seconds and then turn it off regardless of how long the switch is on for. We can do this with a simple external timer. But what if the process included 10 switches and solenoids? We would need 10 external timers. What if the process also needed to count how many times the switches individually turned on? We need a lot of external counters.

As you can see the bigger the process the more of a need we have for a PLC. We can simply program the PLC to count its inputs and turn the solenoids on for the specified time.

This site gives you enough information to be able to write programs far more complicated than the simple one above. We will take a look at what is considered to be the "top 20" plc instructions. It can be safely estimated that with a firm understanding of these instructions one can solve more than 80% of the applications in existence.
That's right, more than 80%! Of course we'll learn more than just these instructions to help you solve almost ALL your potential plc applications.

CRM

Thank you very much for the details,and also for where to look for more details (at http://www.plcs.net).

dear Mr.Mani

To day PLC operated process is so common you will find them every where from Drycleaning machines to food process plants, Power generating plants to sailing Huge cargo ships.Allenbradely,Honeywel are some of the major players in this field.

CRM

http://en.wikipedia.org/wiki/Programmable_logic_controller

Thank you.The website referred is very informative. Mostly it describes the concepts / basic theory. Along with, I need to know practical applications where PLCs are in use?

There are tens of thousands of practical applications for PLCs. The car you drive was most likely built on an assembly line controlled at least in part by PLC's. The beverage you drink from a can was most likely filled and sealed on a production line being controlled by a PLC. Many modern Roller Coasters are controlled using PLCs as well as other ammusement rides.

...in the USA?

In the UK it is illegal to use electronic devices for safety interlocking in public transport systems. Any electronic system must have a hard-wired safety interlock supervising it; reference the Docklands Light Railway in London.

Older machines uses dozens of reles and temporizators for make your functions. Standar was one rele for each external signal (sensor, switches), one rele for each output (electrovalve, contactor, lamp, motor) and others reles for logic and temporization. Newer machines need only one PLC with multiples inputs and outputs for the same functionality. Changes in system were made chaneging wires and connections. Today, with PLC, changes are made by software. No screwdriver requiered. El español es mi lengua madre, pero mi escaso ingles puede ser util.

If you want see aplication , go to GlobalSpec search "Programmable Logic Controller" them have 450 companies to have all you do need.

Tomás

• A fully-automatic water treatment plant in East Kilbride that produces 80m³/d of water with a resistivity of 18.2MΩ-cm.
• A similar plant at 364m³/d in Singapore.
• A fully-automatic condensate polishing plant for a power station in Jersey.
• A fully-automatic water pretreatment plant for cleaning up 25m³/h Town Mains water in Baku.
• Service selection and temperature control systems for brine/cooling water/steam services on reactor jackets for pharmaceutical manufacture in Dagenham.
• A pharmaceutical recrystallisation plant in Dagenham.
• A user interace for a water treatment plant for an oil refinery in Teeside.
• A control system for a gelatine routing system for photographic materials manufacture in Harrow.
• A control system for an automatic emulsion washing plant (ultrafiltration) for photographic materials manufacture in Harrow.
• A fully-automatic 40000m³/d tertiary effluent recycling plant in Ulting.

Etc., etc.

Some of the processes I have used PLCs in are

• Lumber of wood sorting, stacking and grading
• Steel and wire rolling mills
• Plasterboard or Drywall production
• Water Treatment works
• Just about everything you can think of with mining just about everything
• Brick manufacturing
• MDF and particle board manufacture
• Grain silo and transportation control
• Conveyor belts carrying just about anything you can think of
• HVAC local control
• Data gathering and local control in conjunction with complex computer control and automation. In other words the real work interface and front end processing and control.
• Home automation and security

The thing about PLCs is that their use is only limited to your own imagination. Put simply they are a microprocessor based computer control system that is specially designed so that it can be directly used to control real world systems that require the sensing and switching of mains type voltages and currents. The concept is built around an off the shelf system that can easily be wired to any common type sensing equipment via a range of off the shelf input output modules. The only thing that you need to do is wire the thing in and program it accordingly.

Initially the way they were programmed in a way very similar to the ladder diagrams that many hard wired control panels used. As they became more sophisticated various other programming techniques were introduced but most still have some sort of ladder diagram programming available.

They are probably the most under utilized piece of automation and control equipment that has ever existed. I think the main reason for their underutilization is that many people do not understand how versatile they actually are and how easy they are to use. Considering you can now purchase a base level one for less than US$100 there are few control applications that they could not be used in.

Some traffic light here in the USA is controlled by the PLC. As a matter of fact, when I was learning how to program a plc, one of the exercise is to program a traffic light signal to turn on and off those lights.

MidniteFighter

Will it be possible to give a step by step approach, in the design exercise of this PLC program "a traffic light signal to turn on and off lights", so that it can help in training session?