How does a PLC panel work? What are all the components and why do they need to be installed? Well, you’re in luck! Here’s a closer look at how a common PLC panel and its components work…
1. What is a PLC control panel?
PLC panels are steel boxes that contain the electrical components needed to run a factory machine. PLC stands for Programmable Logic Controller. Usually found in factory control panels, PLCs are industrial-hardened computers. High-voltage components make up many of the other items found inside.
2. Composition of PLC control panel
The following are the components of the PLC control panel:
1) PLC panel: Power components:
- Rotate off
- Power distribution block
- Branch circuit breaker
- Power supply
- Motor starter
- Variable frequency drive (VFD)
- Motor soft starter
2) PLC panel: control components:
- Auxiliary circuit breaker
- Master Control Relay (MCR)
- Ethernet switch
- Programmable Logic Controller (PLC)
- Human Machine Interface (HMI)
- Input/Output (IO) Modules
- Action button
3. How does the PLC control panel work?
In all PLC functions, there are four basic steps: input scan, program scan, output scan, and housekeeping. These stages are repeated again and again in a cyclical pattern. There are four steps in the operation of PLC.
1) Input scan
Use this function to detect the status of all input devices connected to the PLC.
2) Program Scanner
This function executes the logic of a user-created program.
3) Scan output
Activates or deactivates the operation of all output devices linked to the PLC.
4) General Cleaning Services
Communication with the programming terminal, internal diagnostics, and other tasks are performed during this phase.
Power distribution controllers (PLCs) are complex and powerful computers that receive data, execute logic on the data in the CPU, and turn outputs on or off based on the logic. Take the following scenario as an example:
The CPU keeps track of the state of various inputs (e.g. The proximity sensor is off, the valve is 40% open, etc.)
The CPU takes the information it receives from the input and applies logic to the information it receives.
The CPU controls the outputs according to the logic (for example, turning off the motor, opening the valve, etc.).
Control system engineers develop communication software that allows PLC panels to communicate with each other over the network using a variety of different protocols. In PLC-based panels, HMI/MMI displays various messages and controls for the operator. To maintain effective control over the system.
4. What material is used for the PLC panel?
- Painted carbon steel
- Stainless steel
- Glass fiber
5. Where is PLC used?
In smart buildings, PLCs are used to control elevators or turn on and off light switches. PLCs are used to monitor security cameras and automatic warning devices, traffic lights, and industrial processes such as cutting glass and paper. The PLC monitors runtime data such as equipment uptime, operating temperature, and usage statistics. It also starts and stops processes and generates notifications if the machine fails.
PLCs are used in product assembly, packaging, motion control, batch control, machine diagnostics and testing, and robotic processes.
6. How is PLC programmed?
Ladder logic is commonly used to program PLCs, but other languages such as Function Block Diagrams, Structured Text, Sequential Function Charts, and Instruction Lists are also used. Ladder logic uses a graphical diagram based on relay circuit hardware to express and specify the logical structure of a process in a PLC software application. The ladder logic code looks like an electrical schematic.
7. Advantages of PLC panel
- Very fast
- Ease of changing logic is flexibility
- Reliable due to no moving parts
- Low power consumption
- Modular assembly for easy maintenance
- Fault Finding and Diagnostic Equipment
- Able to handle very complex logic operations
- Good documentation facilities
- Easy to couple with the process computer
- Analog signal processing and closed-loop control programming
- Programmable counters, timers, and comparators
8. Choose the right processor
For selecting a modular processor, the most important criterion is the number of I/O points. Each PLC processor can only work with a limited number of I/O modules. A processor’s memory size (for data storage or program storage) and performance (scan time) are also important considerations. The size of the program depends on the complexity of the control problem and the skill and style of the programmer.
A PLC with the appropriate memory size and speed need to be selected according to the application.
Purge and pressurize panels
Fire and explosion-proof panel
SIL Safety PLC System
distributed control system
IEC 61439 Type Test Assembly Panel
9. Common questions
Here are some frequently asked questions about PLCs:
1) What is the difference between PC and PLC?
PLCs are often described as “rugged digital computers,” but there are some key differences between the two.
While a PC is required to run a PLC, a PC does not require a PLC to function. This is because PLCs run on microcontrollers, while PCs run on microprocessors.
PLCs use a scan-based approach to code execution, while PCs use an event-based approach to code execution.
PLC inputs are signals rather than data inputs from PC drives. Data from PLCs are often collected by PCs and used to trigger work orders, reports, and notifications.
PLCs’ operating systems are designed to perform control tasks, so unlike PCs, they typically do not use antivirus or registry cleaning utilities.
Ladder logic or proprietary vendor languages are used to program PLCs. PCs are programmed using high-level languages such as Java or C++.
PLCs are not immune to cybersecurity attacks and malware, but fewer instances have been reported than PCs. This is because PLCs have limited functionality compared to PCs.
Small PLC systems are usually less expensive than PCs for similar use cases, but large PLC systems required for complex logic operations can be expensive. PLCs are less expensive to physically maintain as they are better suited to harsh environmental conditions.
2) What is the difference between relay logic and ladder logic?
The control circuitry in the relay logic system needs to be hardwired for each control function. The logic and control functions of relays are based on physical electronic circuit diagrams.
A programmable microprocessor-based PLC performs logic and control functions using ladder logic. PLCs store ladder logic programs in memory. Unlike hardwired control systems, PLCs can be reprogrammed, saving time and money because expensive wires and cables do not need to be replaced. Only the I/O devices in the PLC need to be hardwired.
3) How are microcontrollers and microprocessors different?
Microprocessors and microcontrollers are sometimes used interchangeably, but there are significant differences between them. A microprocessor chip has only one CPU. A microcontroller consists of a CPU, memory, and input/output (I/O) modules, all embedded on a single chip.
A microprocessor cannot operate independently of other components, such as additional circuitry and memory, I/O modules, and software.
Microprocessors are used when a lot of complex processing is required, such as games and laptops, and when the task is undefined. In electronic equipment and industrial machines, microcontrollers perform repetitive, predefined tasks.
Microcontrollers are cheaper, smaller, and consume less power than microprocessors.
The importance of a robust and reliable control panel design cannot be overemphasized. Commercial control panels can handle hardware and software features and function more efficiently. All major components of the control panel should be well organized and optimized to provide the best performance at all times.