Programmable Logic Controllers (PLCs) play a critical role in industrial automation, enabling precise control and monitoring of machinery and processes. To effectively navigate the world of PLCs, it is essential to grasp the key terminologies associated with this technology. Understanding PLC terminologies such as inputs, outputs, ladder logic, and scan cycle is fundamental to programming and operating PLCs.
This knowledge empowers engineers and technicians to design, troubleshoot, and optimize automation systems with precision and efficiency. In this article, we will explore the essential PLC terminologies, providing a solid foundation for harnessing the full potential of PLCs in industrial settings. Let’s dive into the world of PLC terminology and unlock new possibilities in automation and control.
A
Analog Input
Analog inputs are used to read continuous, variable signals from the environment. Think about it like a dimmer switch on a light – it’s not just ‘on’ or ‘off’, but it can be set to any level of brightness in between. So, if you have a sensor that can measure a wide range of values, it sends this data to the PLC as an analog input.
The PLC then uses this data to make decisions or control processes. Analog inputs are important for accurate measurements, like temperature control in chemical plants.
Analog Output
Analog outputs, on the other hand, are used to control or adjust variables in a system. Analog output instructs a dimmer switch to adjust brightness according to desired levels. It tells the switch how much brightness to provide.
This could be based on certain conditions or rules set up in the PLC. PLCs use analog outputs to control valve flow and adjust water flow as needed. Analog outputs enable precise management and optimization of processes in a control system.
B
Backup Battery
A backup battery in a PLC is like a safety net. Imagine you’re working on your computer and suddenly there’s a power cut. Without a backup battery, you’d lose all your work! Similarly, The backup battery in a PLC ( Programmable Logic Controller) prevents data loss during power outages. keeping the system running smoothly.
It helps the system run smoothly and prevents disruptions. That could affect important processes.
Baud Rate
The baud rate is like the speed of conversation between devices. When devices “talk” to each other in a PLC system, they exchange information in a language made up of bits.
The baud rate tells us how many bits are sent per second. A higher baud rate means more bits can be sent in the same amount of time, leading to faster communication.
Binary Coded Decimal (BCD) Input
BCD input is a way of representing decimal numbers in a format that PLCs can understand. You can think of it like a translator that converts regular numbers into a special code of 1s and 0s.
This way, PLCs can work with common decimal numbers. While still using their preferred language of binary code. BCD inputs are often used in PLCs to read data from devices like keypads or displays.
Boolean Logic
Boolean Logic is like the ‘yes’ or ‘no’ language for PLCs. It is named after George Boole. A mathematician came up with a system of logic that only has two values: true or false. In the world of PLCs, this logic to make decisions.
For example, if a light switch is on (true/1), the PLC might decide to turn on a fan. If the switch is off (false/0), the fan stays off. This kind of simple, binary decision-making is the heart of PLC operation.
C
Certification
PLCs can earn certificates, like students after exams. UL and CE are organizations providing these certificates.
They ensure safety, reliability, and compliance with standards. Such as electrical safety and environmental impact.
A PLC with such a certificate is trusted to perform its job well, like a seal of approval.
Communication Ports
Communication ports in a PLC are like the doors and windows in a house – they’re how information gets in and out. Different types of ports are used to connect the PLC to other devices or networks.
For example, an Ethernet port might connect the PLC to a computer network. RS232 or RS485 ports can connect it to devices like printers or scanners.
Compact or Brick PLC
A compact or brick PLC is like a suitcase packed with everything you need for a trip. Compact PLCs have fixed and built-in components. Unlike larger modular PLCs that offer flexibility for additions or rearrangements.
They’re typically smaller and less expensive than modular PLCs. Compact PLCs are suitable for simpler systems, offering less flexibility and expandability requirements.
Control Method
The control method guides a PLC in performing its tasks. It includes simple actions like turning motors on/off. Complex operations like adjusting conveyor belt speed based on objects. And managing entire processes in manufacturing lines.
The control method is determined by customized programming to suit specific application requirements.
Count Value
A count value is like a digital scorekeeper for a PLC. For example, every time a product passes by a sensor on a production line, the count value might go up by one.
This allows the PLC to keep track of how many times an event has happened or how many objects have been processed. This count can then be used for tasks like inventory management or quality control.
Counter Reset Modes
Counter reset modes determine when the count value resets to zero. like resetting a stopwatch. It can be done manually, automatically after a set time, or triggered by specific events.
This feature is crucial for starting the count anew, like at the beginning of a production batch.
Current Consumption
Current consumption is the amount of electrical power a PLC uses to do its job. Monitoring a PLC’s current consumption, like tracking your car’s fuel consumption. It helps identify issues and areas for improvement.
If the PLC is using more power than expected. for example, it could mean that there’s a problem with one of its components.
D
Digital Input
Digital input is like a light switch; it’s either ‘on’ or ‘off’, there’s no in-between. In a PLC, digital inputs come from devices that only have two states, like a button being pressed or not.
When the button is pressed, the digital input might be a ‘1’ (on), and when it’s not pressed, the input might be a ‘0’ (off). PLCs utilize binary information for decision-making and process control.
Digital Output
The digital output is the instruction from a PLC to a connected device; again, it’s like a light switch that can be ‘on’ or ‘off’. For example, if a PLC receives a digital input that a button has been pressed. It might send a digital output to turn a light on.
And when it receives an input that the button isn’t pressed anymore, it might send an output to turn the light off. In this way, digital outputs are how the PLC communicates its decisions to the rest of the system.
E
Electrical Isolation
Imagine you’re at a party and it’s too noisy to have a conversation. Electrical isolation is like going to a quiet room to talk without all the noise. In a PLC, it’s used to separate different parts of the system so they don’t interfere with each other.
This way, if there’s a problem like a power surge in one part, it doesn’t affect the others. This helps keep the PLC and its connected devices safe and working properly.
Electrically Erasable Programmable Read-Only Memory (EEPROM)
EEPROM is like a book that a PLC can read over and over again, but also erase and rewrite when needed. It’s a type of memory that stores the PLC’s program – the set of instructions it uses to do its job.
And even if the PLC loses power, the information in the EEPROM isn’t lost. Just like how a book doesn’t lose its words if you close it.
EMC (Electromagnetic Compatibility)
EMC is like a rule that says all electronic devices have to play nice together. Technically, EMC ensures devices don’t cause interference and function properly. Even when exposed to interference, like radio static.
For a PLC, having EMC certification means it won’t mess with other devices in the system. It can do its job effectively even in a ‘noisy’ electromagnetic environment.
Erasable Programmable Read-Only Memory (EPROM)
EPROM is like a chalkboard for a PLC. It’s a type of memory that can be written to with new information (like writing with chalk). But also erased when it’s no longer needed (like wiping the chalkboard clean). However, to erase an EPROM, you need a special tool: ultraviolet light.
Once it’s erased, new data can be written onto it. In a PLC, EPROM might be used to store the program that tells the PLC how to operate.
External Power Supply
An external power supply is like the plug that powers your TV – it’s outside the TV but connected to it. In the same way, a PLC might have an external power supply that’s not built into the PLC itself. But provides it with the electricity it needs to work.
This can be useful because it means the PLC can be used with different power supplies. It depends on what’s available or needed for a particular system.
F
Fail-Safe Circuit
Imagine you’re on a roller coaster and the power goes out. You’d want to know that there’s a system in place to safely bring you back down. That’s essentially what a fail-safe circuit does in a PLC. It’s a design that ensures if something goes wrong; the system will still go to a safe state.
It may involve machine shutdown, alarm sounding, or safety mechanism activation. It aims to prevent accidents and minimize damage during unexpected situations.
Field bus Protocols
Field bus protocols are like the rules of a conversation. When devices in a PLC system ‘talk’ to each other, they need to follow certain rules so they understand each other. That’s what field bus protocols are.
They define things like how data should be formatted. How devices should take turns talking, and what to do if a message doesn’t get through. With a shared field bus protocol, devices in a system can communicate efficiently.
H
Hardware Fault
Imagine a Hardware Fault as a flat tire on a bicycle. Physical issues with the PLC’s components can disrupt its proper functioning. This might be a faulty wire, a damaged chip, or a worn-out connector.
Detecting these faults quickly is crucial to keep the PLC system running smoothly. It’s like having regular checks on your bicycle to ensure the tires are properly inflated. There are no loose screws, so you can enjoy a safe and smooth ride.
High-Speed Counters
High-Speed Counters in PLCs are like super-fast scorekeepers at a sports game.
This is important in industries like packaging. Where items on a conveyor belt need to be counted accurately at high speeds. These counters help the PLC maintain accuracy in processes where timing is critical.
Human Machine Interface (HMI)
An HMI is like the display and buttons on your microwave. It’s the way people can interact with the PLC system. It could be a touchscreen, a keyboard, or buttons and lights.
The HMI allows users to send commands to the PLC. It also receive information from it (like when the cooking time is up). It’s a vital component for efficient control and monitoring of industrial processes.
I
I/O Control Method
The I/O Control Method is like the traffic controller at a busy intersection. It determines how the inputs and outputs are managed.
Similar to a traffic controller directing cars for smooth traffic flow. The I/O control method in a PLC determines when and how inputs are read and outputs are sent. This ensures efficient control of industrial processes, optimizing their operation.
Input Interrupts
Imagine if you’re reading a book and your phone rings. You’d stop reading to answer it, right? That’s what Input Interrupts are like in a PLC. They’re signals that tell the PLC to stop. What its doing and handle something important right away, like a safety alert.
Once the interrupt is dealt with, the PLC can go back to its regular tasks. These interrupts ensure urgent signals don’t get missed in the routine operations.
Input Module
An Input Module is like your ears or eyes. It’s a part of the PLC that receives information from the outside world, like sensors or switches. Like eyes see light and ears hear sound, an input module takes in signals about system conditions. Such as machine status or process temperature. This information is then used by the PLC to control the system based on its programmed logic.
Input Voltage Level
The Input Voltage Level for a PLC is like the water pressure in your shower. It’s the ‘strength’ of the electrical signal coming into the PLC from an input device, like a sensor or a switch. Just like you’d want the right water pressure for a comfortable shower. PLC requires signals at the correct voltage for accurate reading and response.
Input/Output Addressing
Input/Output Addressing in a PLC is like putting labels on boxes in a warehouse. Each input and output in the PLC has a unique address or label, which helps the PLC identify and locate them easily.
Just as a warehouse worker can find a specific box by its label. The PLC uses these addresses to know exactly where to get input data or send output instructions.
Instruction Execution Time
Instruction Execution Time refers to the duration for a PLC to execute a command. similar to completing a task on a to-do list. It can involve simple actions, like turning on a light, such as adjusting machine speed. Minimizing these times enhances system control efficiency and enables swift response to changes.
Instruction Set
An Instruction Set for a PLC is like a cookbook for a chef. It’s a collection of all the ‘recipes’ or commands that a PLC can use to do its job. Each instruction guides the PLC to perform a specific task. It is like comparing values or moving data.
Just like a chef uses different recipes to make different dishes. A PLC uses different instructions to control a wide range of industrial processes.
IP Rating (Ingress Protection)
An IP Rating is like a suit of armor for a PLC. It tells you how well the PLC is protected against things like dust and water. The higher the rating, the stronger the protection.
For example, a PLC with a high IP rating might be able to work in a dusty factory or outdoors in the rain. Similar to a knight’s armor for battle. A PLC needs the right IP rating to ensure safe and reliable operation in its environment.
L
Linear Counting Mode
Linear Counting Mode in a PLC is like counting steps on a fitness tracker. It’s a method for tracking consecutive events in a straightforward, linear sequence. For instance, if you’re monitoring a conveyor belt. You might use linear counting mode to count how many boxes pass by a sensor.
Like the step count on your fitness tracker going up with each step you take. The count in the PLC increases with each box that passes.
M
Memory Card Slot
A Memory Card Slot in a PLC is like a backpack for a hiker. It’s a place where additional ‘storage space’ can be added, in the form of a memory card. This extra memory can be used to store more program data or to save important information.
Just as a hiker uses a backpack to carry more supplies for a long journey. A PLC can use a memory card slot to handle larger or more complex tasks.
Modular PLC
A Modular PLC is like a Lego set. It’s made up of different ‘blocks’ or modules that can be added, removed, or replaced as needed. These modules can include things like input/output units, communication modules.
Just like you can build different things with the same Lego set by rearranging the blocks. A modular PLC can be customized to suit different industrial processes.
N
Network Interface
A network interface in a PLC serves as a connection point. And allowing communication with other devices and networks. It facilitates data exchange between the PLC and external components.
The network interface enables smooth communication for the PLC. Allowing it to receive and send information to control and monitor processes.
Noise Filter
A noise filter reduces unwanted electrical noise in PLC systems. Electrical noise can be caused by factors like electromagnetic interference or voltage fluctuations. Which can disrupt the signals in the PLC.
The noise filter acts as a barrier, blocking or reducing this unwanted noise. The noise filter helps maintain signal quality by minimizing electrical disturbances. Ensuring accurate and reliable operation of the PLC.
Noise Immunity
Noise immunity is the PLC system’s resistance to electrical noise without affecting performance. PLCs are designed for noisy environments like industrial settings.
High noise immunity enables the PLC to handle disturbances. Ensuring proper functionality and preventing errors or malfunctions.
Non-Fail-Safe Circuit
A non-fail-safe circuit in a PLC is a circuit that does not automatically shut down. In other words, if there is an issue or failure in the circuit, it will continue to operate despite the problem.
Non-fail-safe circuits in a PLC can be risky. And Leading to equipment damage or unsafe conditions. Careful design and management, along with safety measures. Ensure the system’s safe and reliable operation, mitigating potential risks.
Number of Inputs
The number of inputs in a PLC indicates the total signals it can receive from sensors or switches. Each input detects a condition for the PLC to use in decision-making or control actions. The more inputs a PLC has, the more signals it can process and respond to.
Number of Outputs
The number of outputs in a PLC indicates the quantity of control signals it can send to external devices. Outputs enable the PLC to take action based on inputs received. More outputs allow control of more devices or complex tasks.
O
Operating Temperature Range
The operating temperature range determines a PLC’s temperature tolerance without issues or damage.
It includes minimum and maximum limits for reliable operation.
Range critical for optimal performance and preventing malfunctions or failures.
Output Module
An output module in a PLC interface with external devices. Allowing the PLC to send control signals to those devices.
The output module converts PLC signals to activate external devices like motors, solenoids. And Also lights with appropriate voltage levels.
Output modules vary in output quantity. It enables flexible and scalable control of multiple devices simultaneously.
Output Voltage Level
The output voltage level in a PLC refers to the specific voltage at which the PLC delivers signals. It represents the electrical potential difference that the PLC output. It can provide to control connected components such as motors, valves, or lights.
The output voltage level needs to match the requirements. Then connected devices to ensure proper operation and functionality.
Overhead Processing Time
PLC overhead processing handles internal tasks not related to input/output operations.
It includes memory management, communication protocols, and background tasks.
Consider overhead processing time for efficient use of system resources during design.
P
PLC Cycle Time
PLC cycle time is the duration of one full program execution cycle.
It includes input scanning, logic execution, and output updating.
A shorter cycle time means faster control response, important for time-critical applications.
PLC Firmware
PLC firmware is the software controlling its operation. It includes instructions, logic, and control algorithms.
It provides intelligence for specific tasks based on programmed logic.
Firmware updates allow customization and adaptation to different applications or requirements.
PLC Programming Cable
A PLC programming cable connects a computer or programming device to a PLC.
It transfers programming code, configuration settings, and data for programming or debugging.
The cable uses a specific connector type compatible with the PLC’s communication port.
PLC Programming Languages
PLC programming languages are used to create control logic for a PLC.
They provide a structured framework for writing instructions and defining PLC behavior.
Common languages include ladder logic, structured text, and function block diagram. And also a sequential function chart.
Each language offers unique syntax and features for different programming styles and applications.
PLC Scan Cycle
The PLC scan cycle refers to the sequential process that a PLC follows during its operation. It involves scanning inputs, executing the program logic, and updating outputs. During the scan cycle, the PLC reads inputs, and evaluates logic. It updates outputs based on the inputs.
The scan cycle repeats at set intervals for real-time control. And Also monitoring of connected devices.
PLC State
The PLC state represents the operational condition of the PLC.
“Run” means the PLC is executing the control program and responding to inputs and outputs.
“Stop” means the PLC is halted and not processing any logic.
“Fault” indicates an error or abnormal condition, often requiring troubleshooting or maintenance.
Other states may include “Program” for programming mode and “Test” for diagnostic purposes.
Monitoring the PLC state is crucial for operation and troubleshooting.
Power Supply
The power supply in a PLC provides electrical power.
It converts input power to the required voltage and current.
The power supply ensures stable and reliable power distribution for proper PLC operation.
Processing Speed
Processing speed is the CPU’s instruction and calculation rate in a PLC.
It affects input processing, control logic execution, and output generation speed.
Higher processing speed allows quicker response. And efficient handling of complex control tasks in a PLC.
Processor Unit
The processor unit is the central component that handles processing. It controls function in a PLC. It consists of the CPU, memory, and other supporting circuitry.
The processor unit reads inputs and executes the programmed logic. It generates outputs based on the control algorithms. It serves as the brain of the PLC, coordinating and managing the overall operation of the system.
Program Memory Capacity
Program memory capacity is the available memory in a PLC for storing the control program. It determines the maximum size of the program that can be stored in the PLC.
Program memory capacity impacts control logic complexity and functionality.
More capacity allows for extensive control algorithms, accommodating complex automation tasks.
Programmable Read-Only Memory (PROM)
PROM is non-volatile memory in PLCs for permanent program data storage.
It stores unchangeable programming code or data, retaining content even without power.
This makes PROM suitable for critical or fixed information storage in PLCs.
Programming Port
The programming port is a dedicated interface on a PLC.
that enables the communication between a programming device and the PLC.
It allows for transferring programming code, and configuration settings. Data for programming, monitoring, or debugging the PLC.
Pulse Width Modulated (PWM) Output
PWM output is a control technique used in PLCs to generate variable voltage. It rapidly toggles the output signal between ON and OFF states at a fixed frequency.
This modulation technique allows for precise control of the average output level. Enabling applications such as motor speed control or dimming of lights.
Q
Quick-Response Inputs
Quick-response inputs in a PLC swiftly detect and respond to changes in input signals. These inputs are designed to have minimal delay or response time. It Ensures fast and accurate detection of input state changes.
Quick-response inputs are used for real-time monitoring or high-speed input processing in applications.
R
Rack-based PLC
A rack-based PLC has modular components mounted in a rack.
The rack allows easy installation and system expansion.
Modules can be added or removed for flexible configuration and scalability.
Random-Access Memory (RAM)
RAM in PLCs stores temporary data and program instructions during runtime.
It offers fast access for processing variables, intermediate results, and program execution data.
RAM contents are lost when power is removed, requiring data to be saved in non-volatile memory.
Read-Only Memory (ROM)
ROM is non-volatile memory in PLCs for permanent program instructions or unchangeable data.
It holds pre-programmed firmware and fixed program data that remains constant during runtime.
ROM retains its content even when power is removed from the PLC. Ensuring that critical program instructions or data are always available. When the PLC starts up.
Real-Time Clock
An RTC in a PLC provides accurate time and date information. It allowing time-based operations and task scheduling.
It ensures that the PLC can perform time-critical functions. Such as time-based control actions, event scheduling, or time stamping of data. The real-time clock is powered by a backup battery. It ensuring that it continues to keep time even when the PLC is powered off.
Relay Output
A relay output in a PLC refers to an output channel. That uses electromechanical relays to control external devices. The relay output provides electrical isolation between the PLC and the connected equipment. Current levels without directly affecting the internal circuitry.
It enables the PLC to turn on or off devices such as motors, lights. It also solenoid valves by energizing or de-energizing the relay coil.
Ring Counting Mode
Ring counting mode is a counting mode available in some PLCs. It involves incrementing or decrementing a counter value based on a specific condition. Such as the rising or falling edge of an input signal.
In-ring counting mode, the counter loops back to its minimum or maximum value. Once it reaches its maximum or minimum limit respectively. This mode is useful in applications where continuous counting is required. Allowing the counter to wrap around and continue counting without interruption.
S
SCADA System
SCADA stands for Supervisory Control and Data Acquisition. It remotely monitors and controls industrial processes.
Components include sensors, PLCs, HMIs, communication networks, and a central supervisory system.
SCADA collects real-time data, displays it, and enables control actions. It is used in manufacturing, utilities, and transportation sectors.
Sink Output
A sink output in a PLC refers to an output channel that is capable of sinking current. The output provides a path to ground or common reference for the connected load. When the sink output is activated, it allows current to flow from the load to the PLC, completing the circuit.
Sink outputs are commonly used when connecting to devices. When the load is wired in a common negative configuration.
Software Fault
A software fault in a PLC refers to an error or malfunction that occurs within the PLC’s software program. It can result from unexpected conditions during program execution. Software faults can lead to incorrect or unintended behavior of the PLC. And potentially affecting the control and operation of connected devices.
Software testing, debugging, and quality assurance practices minimize faults. It ensuring the reliability and stability of the PLC system.
Source Output
A source output in a PLC refers to an output channel that is capable of sourcing current. The output provides the power or voltage source to the connected load. When the source output is activated. It supplies current or voltage to the load, enabling the circuit to operate.
Source outputs are commonly used when connecting to devices. That require a sourcing signal or when the load is wired in a common positive configuration.
Storage Temperature Range
Storage temperature range ensures safe device storage without functionality impact or damage.
It specifies optimal temperatures to prevent degradation or failure. Storing outside range reduces lifespan, data integrity, and causes irreversible damage.
T
Transistor Output
In a PLC, a transistor output is a channel using transistors for switching. It controls high-current/voltage devices.
Transistor outputs interface with external devices like solenoids, motors, or relays. They provide low-power control signals to switch higher-power devices.
W
Watchdog Timer
A watchdog timer monitors PLC software, checking if it runs as expected. It detects errors or program stops.
If no signal is received within a set time, it triggers PLC reset and recovery process.
The watchdog timer maintains system reliability by detecting and recovering from software failures.
Conclusion
In conclusion, understanding the key terminologies related to Programmable Logic Controllers (PLCs) is crucial for effective programming and operation in industrial automation systems. From inputs and outputs to ladder logic and scan cycle, these terminologies form the foundation of PLC functionality.
By mastering these concepts, users can optimize their PLC programming, enhance system performance, and unlock the full potential of PLCs in various industrial applications. Continuous learning and familiarity with PLC terminologies will empower individuals to tackle complex automation challenges and drive efficiency in control systems.