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Friday, April 22, 2011

PLC History


PLC History
 PLC development began in 1968 in response to a request from an US car manufacturer (GE). The first PLCs were installed in industry in 1969.
Communications abilities began to appear in approximately 1973. They could also be used in the 70′s to send and receive varying voltages to allow them to enter the analog world.
The 80′s saw an attempt to:
standardize communications with manufacturing automation protocol (MAP), reduce the size of the PLC, and making them software programmable through symbolic programming on personal computers instead of dedicated programming terminals or handheld programmers.
The 90′s have seen a gradual reduction in the introduction of new protocols, and the modernization of the physical layers of some of the more popular protocols that survived the 1980′s.
The latest standard “IEC 1131-3″ has tried to merge plc programming languages under one international standard. We now have PLCs that are programmable in function block diagrams, instruction lists, C and structured text all at the same time.

Programmable Logic Controllers

Programmable Logic Controllers

Finding quality programmable logic controllers at a reasonable price is always a difficult thing to do. When first getting started, most people don't want to invest a lot of money to prove a concept. A great way to get started is to find a good used system on ebay and build your foundation with hardware readily available. That way later on once you're ready to take your concept to full production, you'll already be using the same hardware as your production machines.

PLC Basics

What is a PLC?
You may have heard of Programmable Logic Controllers (PLC), but still find yourself wondering, how to get started learning PLC Basics?  With the the different types of PLC products and brands available, it is easy to get lost before even getting started learning PLC Basics. Today, the most common PLC  products are manufactured by the following companies:
  • Allen Bradley
  • GE Fanuc
  • Klockner Moeller
  • Mitsubishi
  • Omron
  • Schneider Electric
  • Siemens
As you can see, with the various choices in manufacturers all claiming different technology claims, it is easy to wonder where to start
So what exactly is a PLC?
A PLC is a device that gathers information (inputs) and uses a preconfigured program inside (logic) to make decisions and generate desired results (outputs).
How much training is required to learn PLC Basics?
Even PLC experts started their journey to a wealth of PLC knowledge with a few first steps.  The easiest way to start learning about PLCs is to begin by building a solid foundation that all other knowledge will be built upon.  With that in mind, the following books are non-brand specific and will build that solid foundation.
What are some good uses for a PLC?
In case you're looking for a reason to learn about PLCs, here are some great uses for them:
  • Manufacturing - Escalators, lifting operations and complete plant control
  • Food Industry - Filling machines, Batch and Process control
  • Textile Industry - Washing machine controls
  • Plastics Industry - Extruder, Injection molding control systems
  • Agriculture - watering systems
  • Amusement Parks - Roller coaster ride and effects systems
This is just a sampling of how a PLC can help control a process or operation. The 10 billion dollar PLC market continues to grow annually as the technology improves and expands into new applications.



How to find PLC training?

Many individuals struggle to find PLC Training specific enough to address their needs.  The trouble is, Classroom style PLC training is expensive and generic.  It’s almost impossible to learn PLC programming without traveling to a class or searching all over the internet.  Both of these methods waste countless hours searching though unorganized or non pertinent information.  Before investing large amounts of time or money on PLC training, the following resources are a great way to learn the specific pertinent information you’re looking for.
  • Programmable Logic Controllers - Frank D. Petruzella

  • Programmable Logic Controllers - James A. Rehg

  • Introduction to Programmable Logic Controllers - Gary Dunning

  • As you can see, there are many different options to train yourself on PLC Basics.  Building the solid foundation is a key first step to ensuring success down the road.

    How much PLC training is required?

    Because each person’s definition of PLC training is different, there is no single answer. This is why PLC classroom trainings are not the most effective way to learn.  Putting many students with different goals in the same classroom results in a lot of time wasted listening to facts that don’t matter.

    How to maximize the effectiveness of PLC training?

    Understanding what needs to be learned is a key first step. Individuals who have had the most success learning about PLC training apply the following principles.
    1.    Make a list of specific learning objectives.
    2.   Search out those items in books or using other resources.
    Once a solid foundation has been built, it is easy to apply just in time learning principles by contacting training companies and asking about how their training would address remaining learning objectives left over from the initial list.
    PLC training is the start to an incredible journey.  Initial research evaluating the specific learning topics saves time and thousands of dollars worth of formal training. Intuition has brought you here and by continuing to invest in yourself, the technology of the future becomes easier to grasp.


    PLC Programming

    How to Learn PLC Programming?

    You may be familiar various forms of Programmable Logic Controllers (PLC), but still find yourself wondering, how to get started PLC Programming.  Don't worry; it's a completely legitimate question, especially because of the different languages available.  You may commonly find PLC programming using the following methods:
    • Function Blocks
    • Ladder Logic
    • Sequential Function Charts
    • Structured Text
    As you can see, with the various choices in PLC programming languages available, it is easy to wonder where to start.

    Where to use PLC Programming Languages?

    In most cases, each PLC programming language has a unique purpose.  The uses will vary slightly from person to person but here are the general strengths of each PLC programming language:
    • Ladder Logic – Most common, general purpose and easy to troubleshoot
    • Function Blocks – Process Applications
    • Sequential Function Charts – Events occurring over and over in the same order
    • Structured Text –Text based programming option is preferred
    This is just a sampling of the different types PLC programming languages available. Each language has benefits and drawbacks that vary based upon application.

    How Exactly to Learn PLC Programming?

    After identifying the PLC programming language for a specific application, learning objectives become easier to focus on. The resources below are some great places to get started.

    The Hands on Approach to PLC Programming

    If you’re the type of person who learns best by doing, a simulator with instruction manual may be a great place to start.  Simulators also come in handy down the road for testing out logic when you cannot take down a machine to try something out.



    PLC Manual


    What does ‘PLC’ mean?
    A PLC (Programmable Logic Controllers)  is an industrial computer used to monitor inputs, and depending upon their state make decisions based on its program or logic, to control (turn on/off) its outputs to automate a machine or a process.
    NEMA defines a PROGRAMMABLE LOGIC CONTROLLER as:
    “A digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions by implementing specific functions such as logic sequencing, timing, counting, and arithmetic to control, through digital or analog input/output modules, various types of machines or processes”.
    Traditional PLC Applications
    *
    In automated system, PLC controller is usually the central part of a process control system.
    *To run more complex processes it is possible to connect more PLC controllers to a central computer.
    Disadvantages of PLC control
    - Too much work required in connecting wires.
    - Difficulty with changes or replacements.
    - Difficulty in finding errors; requiring skillful work force.
    - When a problem occurs, hold-up time is indefinite, usually long.
    Advantages of PLC control
    * Rugged and designed to withstand vibrations, temperature, humidity, and noise.
    * Have interfacing for inputs and outputs already inside the controller.
    * Easily programmed and have an easily understood programming language.
    Major Types of Industrial Control Systems
    Industrial control system or ICS comprise of different types of control systems that are currently in operation in various industries. These control systems include PLC, SCADA and DCS and various others:
    *PLC
    They are based on the Boolean logic operations whereas some models use timers and some have continuous control. These devices are computer based and are used to control various process and equipments within a facility. PLCs control the components in the DCS and SCADA systems but they are primary components in smaller control configurations.
    *DCS
    Distributed Control Systems consists of decentralized elements and all the processes are controlled by these elements. Human interaction is minimized so the labor costs and injuries can be reduced.

    *Embedded Control

    In this control system, small components are attached to the industrial computer system with the help of a network and control is exercised.

    *SCADA

    Supervisory Control And Data Acquisition refers to a centralized system and this system is composed of various subsystems like Remote Telemetry Units, Human Machine Interface, Programmable Logic Controller or PLC and Communications.

    ROM VS Programmable ROM

    ROM

    AMIBIOS BIOSShort for Read-Only Memory, ROM is memory that is capable of holding data and being read from; however, it is not capable of being written to or having its data modified. Unlike RAM, ROM is non-volatile and capable of keeping its contents regardless if it has power or not. A good example of PROM is the computer BIOS as shown in the example picture to the right.

     

     

    Programmable ROM

    Short for Programmable Read Only Memory, Programmable ROM, or PROM is a computer memory chip capable of being programmed. Once the PROM has been programmed, the information written is permanent and cannot be erased or deleted. A good example of a PROM is the computer BIOS.