Programming Device
Chapter-3
A programming device is often a personal computer (PC) with software that enables it to program a PLC.
Often an industrialized PC is used so that it can function reliably in a factory environment.
The programming device frequently has additional functionality depending on the software used.
For example, a programming device running Siemens Totally Integrated Automation Portal (TIA Portal) software is used in all phases of the design, operation, and maintenance of systems that can include PLC'S, HMI'S, PCs, electronic drives, and related devices.
Programming Concepts
There are multiple ways to program a PLC. At one time, PLC programming languages varied with the PLC manufacturer.
In general, however, PLC'S manufactured in recent years are programmed using a language defined in an international specification, IEC 61131.
There are 5 languages that are all a part of the IEC (International Electrotechnical Commission) Section 61131-3 Standard. This IEC Standard allows some ground rules that standardize PLC's and their languages.
The 5 most popular PLC Programming Languages are:
1. Ladder Diagram (LD)
2. Sequential Function Charts (SFC)
3. Function Block Diagram (FBD)
4. Structured Text (ST)
5. Instruction List (IL)
1. Ladder Diagram (LD)
Ladder Diagram was originally modeled from relay-logic which used physical devices, such as switches and mechanical relays to control processes.
Ladder Diagram utilizes internal logic to replace all, except the physical devices that need an electrical signal to activate them.
Ladder Diagram is built in the form of horizontal rungs with two vertical rails that represent the electrical connection on relay-logic schematics.
You can program all the necessary input conditions to affect the output conditions, whether logical or physical.
2. Sequential Function Charts (SFC)
In Sequential Function Charts, you use steps and transitions to achieve your end results.
Steps act as a major function in your program. These steps house the actions that occur when you program them to happen.
This decision can be based on timing, a certain phase of the process, or a physical state of an equipment.
Transitions are the instructions that you use to move from one step to another step by setting conditions of true or false.
3. Function Block Diagram (FBD)
The Function Block Diagram which is also a graphical type of language.
The Function Block Diagram describes a function between inputs and outputs that are connected in blocks by connection lines.
Function Blocks were originally developed to create a system that you could set up many of the common, repeatable tasks, such as counters, timers, PID Loops, etc.
You program the blocks onto sheets and then the PLC constantly scans the sheets in numerical order or is determined by connections which you program between the blocks.
4. Structured Text (ST)
This language is a textual based language.
Structured Text is a high-level language that is like Basic, Pascal and “C”.
It is a very powerful tool that can execute complex tasks utilizing algorithms and mathematical functions along with repetitive tasks.
The code uses statements that are separated by semicolons and then either inputs, outputs, or variables are changed by these statements.
You must write out each line of code and it uses functions such as FOR, WHILE, IF, ELSE, ELSEIF AND CASE.
5. Instruction List (IL)
The Instruction List is also a textual based language.
The Instruction List language resembles Assembly Language. When you use this PLC Programming Language, you will use mnemonic codes such as LD (Load), AND, OR, etc.
The Instruction List contains instructions with each instruction on a new line with any comments you might want to annotate at the end of each line.
Two of the programming languages defined in this specification are ladder diagram (LAD) and function block diagram (FBD).
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