PLC Communications

What is a PLC?

A programmable logic controller (PLC) is a digital computer that is used in industrial automation to automate various electromechanical operations. It was created to address difficulties like high power consumption that occurred when relays were used to regulate industrial operations. It is made up of a programmable microprocessor whose program is produced on a computer and then sent to the PLC through a cable. The program is saved in the non-volatile memory of the PLC.

Programmable Logic Controller(PLC)

History of PLC

PLCs were invented by Dick Morley in 1964. Since then PLC has revolutionized the industrial and manufacturing sectors. There is a wide range of PLC functions like timing, counting, calculating, comparing, and processing various analog signals.

The fundamental advantage of a PLC over a "hard-wired" control system is that after you've programmed it, you can change it for very little money (only the cost of the programmer's work). In a hard-wired control system, you'll have to yank out all of the cables and start over (which is more expensive and takes longer).

Assume you have a light that is controlled by a switch. In general, the light has two modes of operation: ON and OFF. You've been given the responsibility of turning on the switch and waiting 30 seconds for the light to turn on. We're stuck with this hard-wired system. Only by entirely rewiring our circuit to include a timing relay will we be able to do this. That's a lot of work for such a small change.

Light Switch

This is where a programmable logic controller (PLC) comes in, which doesn't require any additional wire or hardware to ensure that a change is made. Rather, a simple update in code is required, which instructs the PLC to turn on the light 30 seconds after the switch is switched on. As a result, including many inputs and outputs is simple when utilizing a PLC.

How does a PLC work?

The programmable logic controller collects data from linked input devices and sensors, analyses it, and then triggers appropriate outputs based on pre-programmed settings. A PLC can quickly monitor and record runtime data such as operating temperature, machine productivity, alert generating when a machine malfunctions, automatic start and stop procedures, and more using its inputs and outputs. PLCs are durable and versatile manufacturing process control systems that can be adapted to a wide range of applications.

Working of PLC

PLC Scan Process

The steps in a PLC Scan Process are as follows:

• The operating system begins cycling and timekeeping. The CPU begins reading data from the input module and verifies all of the inputs' status.
• The CPU begins to run the user or application program, which is written in relay-ladder logic or any other PLC programming language.
• Following that, the CPU takes care of all internal diagnosis and communication activities.
• It inserts the data into the output module based on the program outcomes, updating all outputs.
• As long as the PLC is in run mode, this operation will continue.

Types of PLCs

The two main types of PLC are fixed / compact PLC and modular PLC.

Types of PLC

Compact PLC

There would be multiple modules in a single scenario. It has a set number of external I/O cards and I/O modules. As a result, it lacks the capacity to expand the modules. The manufacturer would choose every input and output.

Modular PLC

Modular PLC is a form of PLC that allows for various expansions through "modules." The number of I/O components can be raised. Because one component is independent of the others, it is easy to utilize.

PLCs are classified as Relay output, Transistor output, or Triac Output PLCs based on their output. Both AC and DC output devices benefit from the relay output type. Switching actions are employed in transistor output type PLCs, which are used inside microprocessors.

A PLC is classified as Mini, Micro, or Nano depending on its physical size.

Communication in PLCs

Because of its capacity to handle a number of connection modalities, the programmable logic controller (PLC) is an appropriate control and data gathering device for a wide range of industrial automation and facility control applications. However, because there are so many options, there is some uncertainty. Let's go over what communications are available and when they should be used to assist clear things up.

PLC networks offer a wide range of networking choices to satisfy your unique control and communication needs. Remote I/O, peer-to-peer, and host computer connections, as well as LANs, are common alternatives. These networks may connect as few as two PLCs, PCs, and other intelligent devices to hundreds of them in a dependable and cost-effective manner.

Many PLC manufacturers provide proprietary networking technologies that are incompatible with other brands of PLCs. This is due to the fact that each manufacturer uses distinct communications protocols, instruction sequences, error-checking techniques, and communication mediums.

It is feasible, however, to have separate PLCs "speak" to one another; all that is necessary is an ASCII interface for the connection(s) and a lot of software work.

Communication Interface Module

Intelligent I/O modules are used to transport data between the CPU and communication networks. These communication modules make it possible to link to other PLCs and computers located at a distance.