PLC Control Systems | ITI Group (2024)

FAQs

What are the basics of PLC control system? ›

A PLC's operation is broken down into three stages: inputs, program execution, and outputs. PLCs capture data from the plant floor by monitoring inputs from any connected machines or devices. These inputs are checked against the program logic, which changes the outputs to any connected output devices.

There are four basic steps in the operation of all PLCs; Input Scan, Program Scan, Output Scan, and Housekeeping. These steps continually take place in a repeating loop. Energizes or de-energize all output devices that are connected to the PLC.

The faults inside PLC are most likely in the output input power supply or channels rather than the CPU itself. Consider any output device that fails of turning on even the LED output is on. If you are testing the output PLC voltage and it indicates normality, then its fault may be the device fault or wiring fault.

Generally, a product life cycle consists of product development, market introduction, growth, saturation, and decline. By studying product life cycle (PLC) stages, companies try to predict the progression of products in the market.

The main components of a PLC consist of a central processing unit (CPU), power supply, programming device, and input and output (I/O) modules. The CPU is the brain of the PLC and carries out programmed operations. These operations or outputs are executed based on signals and data provided from connected inputs.

These three PLC components are: processor, power supply, and an input/output (I/O) section. The processor, or the brain of the PLC system, is a solid-state device designed to perform a wide variety of production, machine tool, and process-control functions.

PLCs take inputs, perform logic on the inputs in the CPU, and then turn on or off outputs based on that logic. Here are some examples of how PLCs can work in industrial settings: The CPU monitors the status of the inputs, e.g. “switch on,” “proximity sensor off,” “valve 40% open”

To check PLC inputs, you need to set your multimeter to the appropriate mode and range, depending on the type of input signal you are measuring. For example, if you are measuring a DC voltage input, you need to set your multimeter to DC volts and select a range that covers the expected input voltage.

– Sinking and Sourcing boil down to defining the direction of conventional current flow between 2 devices. – A Sinking module will have the current flowing into it from the load. – A Sourcing module will have the current flowing into the load from the module.

What are the most common defect of PLC? ›

Module Failure of the Input/Output

This is the most common reason for PLC failures. A telltale sign of input/output PLC system failure is a sudden halt to the process or an irregular performance.

Power Supply Module:

This module is used to provide the required power to the whole PLC system. It converts the available AC power to DC power which is required by the CPU and I/O module. PLC generally works on a 24V DC supply.

Because all PLC input cards read voltage either 0–5V or more traditionally 0–10V. This is because all A/D (analog to Digital) converter chips are voltage input. One big reason is 1–5V is also common in instrumentation.

A reset of the PLC project stops the program and resets the variables to their initialization value. RETAIN variables and PERSISTENT variables are also reset depending on the type of reset.

PLC are divided into three types based on output namely Relay output, Transistor output, and Triac Output PLC. The relay output type is best suited for both AC and DC output devices.

There are two main categories of PLC programming languages. Specific languages used will vary depending on the manufacturer. While some have their own, specialized languages, standard ones fit into one of two categories: textual language or graphical language.