Beginner's Guide to PLC Programming - Engineer and Technician. 77 Pages· · How to Program a PLC (Programmable Logic Controller). By Neal. Omron PLC Beginner Guide - Ebook download as PDF File .pdf), Text File .txt) or read book online. Beginner Guide to PLC - Download as PDF File .pdf), Text File .txt) or read online.
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process is controlled by a ladder program loaded into the PLC CPU memory. signal from various types of automatic sensing and manual input field devices. Lecture – Introduction to PLC's. MME A programmable logic controller ( PLC) . and temperature switches are closed or when the manual . Same basic . basic inputs contacts and output coils and rely heavily upon data stored in the memory of the PLC. The memory of a PLC is organized by types. The memory.
In recent times there have been contenders to replace the PLC but the priniciples and popularity of those early PLC's functions and concepts have continued unabated. It is essential for many people from the technician to the engineer to understand these essential pieces of equipment. Our goal is to make it comprehensive as possible, providing not only the generic principles in all PLCs, but to give practical examples from many different PLC manufacturers. To this end you are welcome to comment on each section by registering as a user and clicking the "add a comment" link at the bottom of the page. I've got the page numbers done. If you wish to be notified of updates then please register for an account and make sure the email notification selection is checked.
To the beginner, it is more valuable than the thick and complex books written by college professors. They cover functions and algorithms you may never use. After wading through one of these, you still might not know how to turn on a motor. And it is written in plain English.
It summarizes dozens of techniques that are needed to write a solid program. It has easy to understand text with relay ladder logic routines that can be used again and again. You learn how to use coils, contacts, internal bits, latches, timers, safety rungs, addressing, inputs, outputs. The good news is that ladder logic, and programmable logic control, is not that hard to understand.
There are just a few essential concepts that you need grasp, and we will share those with you. We know you are busy. This tutorial lets you learn when you have the time. The ebook can be downloaded to your computer, and the tutorial can be viewed online at any time.
You can learn at your own pace. Here is a small excerpt from the book: After the part has been moved into position, the PLC will instruct the machine to clamp the part in place. The solenoid moves the actuator, which holds the part.
You will notice that the branch in the rung contains the logic to provide a manual method of holding the part for machine set-up and maintenance. Then, you can use this bit throughout the program to turn off outputs immediately when the machine shuts down. If the emergency stop is clear, and the machine guard is in place, and there is no system fault the operator may press the start button to set the latch. We could have rearranged any of the bits in this rung, though we would still have to put the latch around the Start pushbutton.
However, to make the rung easier to read, I try to place bits from left to right in order of importance. This module typically lives in the slot beside the power supply. Manufacturers offer different types of CPUs based on the complexity needed for the system.
The CPU consists of a microprocessor, memory chip and other integrated circuits to control logic, monitoring and communications. The CPU has different operating modes.
In programming mode it accepts the downloaded logic from a PC. The CPU is then placed in run mode so that it can execute the program and operate the process.
Since a PLC is a dedicated controller it will only process this one program over and over again. One cycle through the program is called a scan time and involves reading the inputs from the other modules, executing the logic based on these inputs and then updated the outputs accordingly. It's simply a matter of determining what inputs and outputs are needed, filling the rack with the appropriate cards and then addressing them correctly in the CPUs program.
Inputs Input devices can consist of digital or analog devices. A digital input card handles discrete devices which give a signal that is either on or off such as a pushbutton, limit switch, sensors or selector switches. An analog input card converts a voltage or current e.
Examples of analog devices are pressure transducers, flow meters and thermocouples for temperature readings Outputs Output devices can also consist of digital or analog types. A digital output card either turns a device on or off such as lights, LEDs, small motors, and relays. Typical outputs signals can range from VDC or mA and are used to drive mass flow controllers, pressure regulators and position controls.
The most widely used form of programming is called ladder logic. Ladder logic uses symbols, instead of words, to emulate the real world relay logic control, which is a relic from the PLC's history. These symbols are interconnected by lines to indicate the flow of current through relay like contacts and coils.
Over the years the number of symbols has increased to provide a high level of functionality. The completed program looks like a ladder but in actuality it represents an electrical circuit. The left and right rails indicate the positive and ground of a power supply. The rungs represent the wiring between the different components which in the case of a PLC are all in the virtual world of the CPU. So if you can understand how basic electrical circuits work then you can understand ladder logic.
In this simplest of examples a digital input like a button connected to the first position on the card when it is pressed turns on an output which energizes an indicator light. The CPU is then put into run mode so that it can start scanning the logic and controlling the outputs.
Imagine if you will a fifty foot long cabinet filled with relays whose function in life is to control a machine. Wires run in and out of the system as the relays click and clack to the logic. Now imagine there is a problem or a small design change and you have to figure it all out on paper and then shut down the machine, move some wires, add some relays, debug and do it all over again.
Imagine the labor involved in the simplest of changes. This is the problem that faced the engineers at the Hydra-matic division of GM motors in the late 's. Fortunately for them the prospect of computer control was rapidly becoming a reality for large corporations as themselves. So in the GM engineers developed a design criteria for a "standard machine controller". This early model simply had to replace relays but it also had to be: A solid-state system that was flexible like a computer but priced competitively with a like kind relay logic system.
Easily maintained and programmed in line with the all ready accepted relay ladder logic way of doing things. It had to work in an industrial environment with all it's dirt, moisture, electromagnetism and vibration.
It had to be modular in form to allow for easy exchange of components and expandability. The Race is On This was a tall order in but four companies took on the challenge. Information Instruments, Inc. Digital Equipment Corp.
By June of they were selling the first viable Programmable Controller the "" their 84th project which sold over one thousand units. These early experiences gave birth to their next model the "" in which set Modicon as the early leader in programmable controllers. Not to be outdone, the powerhouse Allen-Bradley all ready known for it's rheostats, relays and motor controls downloadd Information Instruments in and began development on this new technology.
By Odo Struger and Ernst Dummermuth had begun to develop a new concept known as the Bulletin PLC which would make them successful for years to come. Allen-Bradley termed their new device the "Programmable Logic Controller" patent 3,, over the then accepted term " Programmable Controller ". The PLC terminology became the industry standard especially when PC became associated with personal computers. Numbers, Codes and a Little Logic At the heart of any computer system are the numbering systems and digital codes used for instructions and memory storage.
Besides the ones and zeros it is important to understand how these bits are packaged into codes like BCD and Gray codes. Understanding these concepts enables the programmer to manipulate the PLC at it's most basic level. Don't you want to feel the power at your fingertips!? Now for the most part these types of concepts will be transparent when programming but there will be occasions when you'll be glad you read this. When the cavemen first started counting they sat around looking at their fingers and stopped at ten.
It took man a little longer to figure out the concept of zero but nobody is perfect. So we've ended up with a common way of counting by 10's which in tech jargon is refered to as base or radix Base or radix refers to the number of symbols you have available to count. We'll see that computers make it more difficult for us lazy humans because they like to count by base-2 binary. In a compromise with computers us humans have developed the base-8 octal or base hexadecimal systems.
Binary People: Learning your 1's and 0's Introduction "There are 10 types of people in the world: Those who understand binary, and those who don't. Consider if you had no choice but to count with only a zero or a one. Pretend that the evil goblin of number snatchers had taken every number from two to nine. How would you count anything? You'd have to do it like 0, 1, 10, 11, , , , and so on. You get the point?