The Rockwell Automation is industry is based in the US and is meant to help industrial automation. Their brands are Rockwell software and Allen-Bradley, and they have more than 20000 employees. They are surely the number one firm for programmable logic controllers.
There are a lot of videos where you can learn the software behind PLCs, but of course, the best comes from the best. Depending on the area you want to focus on, there are many ways you can accomplish it. There are a lot of videos you can learn from and get a better understanding of PLC software.
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About PLCs
Installed PLC is very simple in appearance. You have a input-output devices known as I/O and CPU module. It happens that the I/O is part of the CPU, and it can also be in other modules. The CPU connects with the I/O, so in many systems, they have a backplane which physically maintains them in place and electronically is connecting them. Because a PLC is a computer, you don’t need to limit it to only digital outputs and inputs. As technology advanced, the producer added analog and other numerical outputs and inputs.
Now we can put PID controllers exactly into the PLC program and calculate statistical process control values. As the name says, because it is a programmable logic controller, you have to program it. Almost every PLC is programmed with an application on the desktop PC or laptop. They are connected with the PLC using Ethernet or a private communication bus, it depends on the manufacturer.
Inputs and outputs
When you want to train for working with PLCs, you need to train on it to understand how it works. Videos won’t help you fully understand, you need to experience it from different perspectives which include classes, videos, live practices. You also need to cover problem-solving and troubleshooting skills which are very important when you are working with machines.
The input module of a PLC converts field voltages such as a 120-volt limit switch to a 5 volt DC logic levels. Output modules perform the same function but in reverse order where 5 volt DC is converted to field voltages to control devices such as 120-volt relay coils.
Get more information here: https://www.myplctraining.com/beginners-plc-overview-part-3-of-4-plc-inputs-and-outputs-io/
Processor
The processor is the most important part of a PLC. The code that you made for the machine is stored in the processor. You need to know fundamentals about PLC processor which is like knowing how strong your PC is. On the older version of PLC, the processor was located in the slot of the chassis and these are still being used widely.
Without the software processor is useless, so the most important part about it is the software behind it. It is important to learn from the beginning without shortcuts. These codes can also be copied, so sometimes that is the best way to go because you sometimes need the same instruction that you already made. You can also add things to the existing code, but you need to be really experienced because that is when mistakes are usually made.
Scanning the ladder logic
PLCs control processes by continually scanning the ladder logic program. The scan of a PLC consists of three major steps. First is to check the input status. Next is to execute the program and the last step is to update the output status. This is done constantly, so it is very important.
During the check input status, the PLC determines the state of each input device in the system and writes the values into the input image area. In the next step of the scan cycle, the PLC executes the program one instruction at a time. In the last step of the scan, the outputs are energized or de-energized.
Bits and position
Everything in the PLC boils down to bits within the memory and the memory can be memory attentive and non-memory attentive. It means that if you turn power off to the PLC whether the bits are maintained in the last status which would be memory attentive or if they go back to zero which would be non-memory attentive. Bits are either 1 or 0 and usually, you have an address associated with that bit which determines the spot.
XIC and XIO
The main instruction that everyone will teach you first is XIC or examine if closed and XIO or examine if open. Another extremely helpful way of thinking about these instructions is if and if not. The fundamental confusion regarding the programmed instructions used by PLCs live from the fact to make and break symbols commonly used in PLC programs look like normally open and normally closed contacts and people often mistakenly refer to them in this manner.
PLCs look for logically asserted values and the two instructions respond differently to the logical states of inputs. Make instruction receives a logical zero at the end but it does not allow logical continuity from left to right. If a make instruction or XIC receives a logical at the end, it does allow logical continuity from left to right. When it comes to XIO or break it does the same thing in different order. Read more on this link.
OTE function
OTE is also the basic instruction of a PLC everyone should know and it means output enable. If an output receives a logical zero it is not enabled, if an output receives a logical one it is enabled. The output enables instruction looks remarkably similar to a contactor coil. It is often illustrated in the PLC program as a parenthesis enclosing the output of interest.
Normally a PLC delivers output signals via electromechanical relay for AC or DC loads. If the assigned output receives the logical 0, the output enable instruction, the electromechanical relay coil is de-energized and the contact remains in the deactivated open state whatever load is attached to that contact is similarly de-energized. If an assigned output receives a logical 1, the electromechanical relay coil is energized and the contact is actuated into the activated closed state.
