Hardware for PLCs 211

AC

Alternating current. Electricity that reverses direction at regularly recurring intervals of time. AC switches direction at a frequency of 60 hertz in the United States..

Address

The unique identification of the location of groups of data in the CPU's memory. Addresses correspond to data from specific input and output devices.

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current switches direction at a frequency of 60 hertz in the United States.

amperage

The amount of current flowing in a circuit. Amperage is measured in amperes (A), or amps.

Analog

A continuously variable electrical signal within a given range of values. Analog signals communicate information about variable conditions, such as pressure or temperature.

Backplane

The panel on the back of a PLC rack where I/O modules, the CPU, and the power supply are connected. The backplane provides paths for communication signals.

binary digits

The smallest unit of information on a computer. Binary digits, or bits, consist of 1s and 0s.

Bytes

A group of eight binary digits. Bytes are used to express computer memory size.

Capacitor

An electronic component that stores an electric charge and releases it as needed. Capacitors may be used in CPUs as backup power sources.

central processing unit

CPU. The microprocessor device inside a computer that controls system activities. The central processing unit executes a PLC program and performs all logic activities for the system.

communication module

A PLC component with software and connection ports to enable communication between devices. Communication modules may support multiple communication protocols.

Contaminants

Foreign materal, such as dirt or dust, that can interfere with machine operation. Contaminants can damage the electronic components of a PLC.

Control panels

A group of controls that allow an operator to interact with a specific machine. Control panels usually consist of a display screen and multiple input devices.

CPU

Central processing unit. The microprocessor device inside a computer that controls system activities. The CPU executes a PLC program and performs all logic activities for the system.

DC

Direct current. Electricity that flows in one continuous direction. DC is used in many PLC circuits.

diagnostic

A set of computer instructions that helps users or technicians investigate or analyze the cause or nature of errors or failures. Diagnostic programs in a CPU can help troubleshoot software problems in a PLC.

DIN rail

A metal track or rail, standardized by the Deutsche Institut für Normung (DIN), to which electronic devices can be easily attached or removed. DIN rails are often used in PLCs and electrical panels.

direct current

DC. Electricity that flows in one continuous direction. Direct current is used in many PLC circuits.

Discrete

An electrical signal that is either on or off. Discrete signals are two-state signals.

EEPROM

Electrically erasable programmable read-only memory. A type of read-only memory that can be erased and rewritten with electrical signals. EEPROM is nonvolatile and easy to change.

Electrical signals

Voltage, current, or frequency that communicates information between two devices. Electrical signals are either analog or discrete.

Enclosure

A physical barrier designed to contain and protect the electrical components of a system. Steel enclosures are used to protect PLCs.

Erasable programmable read-only memory

EPROM. A type of read-only memory that can be erased with special ultraviolet tools. Erasable programmable read-only memory protects data from unauthorized changes.

Ethernet ports

A socket or opening on a CPU or computer that accepts an Ethernet cable connector. Ethernet ports allow for high-speed data transmission.

EtherNet/IP

A network communication protocol used for industrial systems. EtherNet/IP uses Ethernet cables for transmission.

faults

A problematic condition that interferes with a component's or system’s ability to function as intended. Faults in PLCs can occur due to software problems or hardware problems.

fiber optic cables

A cable packed with thin, flexible glass or plastic optical fibers that transmit light instead of electricity. Fiber optic cables are used to connect devices such as PLCs and computers.

field devices

An outside component that connects to an input/output module on a PLC. Field devices, also called input/output devices, send signals to and receive signals from PLCs.

fixed PLC

A type of PLC configuration with the CPU, I/O module, and power supply housed in a self-contained unit. Fixed PLCs are often used for applications requiring only basic process control.

flow sensors

A flow control device that measures the speed or quantity of a flowing liquid or compressed gas. Flow sensors are a type of analog input device.

Gateway

A device used to join incompatible hardware components on a network. Gateway devices enable communication between network components with different communication protocols.

handheld programmers

HHPs. A type of proprietary programming device used with specific brands of PLCs to enter program instructions. Handheld programmers have a small display screen and keypad all in one unit.

Hardware

The physical components that form a PLC system. Hardware components for a PLC include the power supply, input and output modules, and the CPU.

HMIs

Human-machine interfaces. A peripheral device connected to a controller that allows an operator to send commands and receive information from connected machines. HMIs usually include a display screen and one or more input devices.

Human-machine interface

HMI. A peripheral device connected to a controller that allows an operator to send commands and receive information from connected machines. A human-machine interface usually includes a display screen and one or more input devices.

I/O devices

Input/output devices. An outside component that connects to an input/output module on a PLC. I/O devices, also called field devices, send signals to and receive signals from PLCs.

I/O modules

Input/output modules. The portion of a PLC that contains connection points for field devices and circuitry to convert electrical current. An I/O module may be input only, output only, or a combination.

I/O points

Input/output points. A connection point on an input/output module for a field device. Input/output points may be discrete or analog.

input devices

A type of field device connected to a PLC that responds to a condition and sends an electrical signal to the input module. Input devices include components such as limit switches, pushbuttons, and sensors.

input modules

The portion of a PLC that receives signals from input devices. The input module reduces the incoming signal voltage and sends it to the CPU.

input signals

An electrical signal from an input device. Input signals enter the input module and are then sent to the CPU.

Input/output devices

I/O devices. An outside component that connects to an input/output module on a PLC. Input/output devices, also called field devices, send signals to and receive signals from PLCs.

input/output module

I/O module. The portion of a PLC that contains connection points for field devices and circuitry to convert electrical current. An input/output module may be input only, output only, or a combination.

input/output points

I/O points. A connection point on an input/output module for a field device. Input/output points may be discrete or analog.

integrated circuits

A complete electronic circuit within a single component. An integrated circuit in a CPU stores program data and allows communication with field devices.

Keyboards

A large keypad including a full set of letters and numbers along with other symbols and commands. Keyboards are included with some control panel HMIs and most PCs.

Kilobytes

KB. A unit of memory equal to 1,024 bytes. Kilobytes are often used to measure the size of small digital files.

limit switches

A mechanical sensor that detects the presence or absence of an object. Limit switches are common discrete input devices.

local area network

LAN. A type of wired network that enables communication between a group of computing devices in a specific geographic location. Local area networks are commonly used by manufacturers and other organizations to store and exchange digital information across a large facility.

Megabytes

MB. A unit of memory equal to about 1 million bytes. Megabytes are often used to measure the size of large digital files.

Memory

The portion of a computer where data is stored. Memory storage can be built into the CPU of a PLC or added in the form of a removable device.

memory card

A removable memory storage device for PLCs, PCs, and other digital devices. Memory cards generally have EEPROM storage.

memory module

A PLC component that provides extra memory storage. Memory modules allow PLCs to store additional programs and data.

micro PLC

A type of fixed PLC with fewer than 36 I/O points. Micro PLCs are used for small-scale applications.

Microprocessor

A computer processor on a small electrical circuit. A microprocessor is responsible for most of the functions of the CPU in a PLC.

Mobile devices

A handheld, portable computer that can connect to the internet. Common mobile devices include smartphones and tablets.

Modbus

A network communication protocol used for industrial systems. Modbus may use either Ethernet cables or serial cables for transmission.

modular PLC

A type of PLC configuration that has a CPU, power supply, I/O modules, and other components that are removable and interchangeable. A modular PLC can be expanded to meet the needs of large-scale applications.

motor starters

A device that safely starts or stops a motor circuit. Motor starters are common discrete output devices.

Multimeter

A device that can measure voltage, current, and resistance. Multimeters are used to verify the voltage of an input/output point on a PLC.

Nonvolatile

A type of computer memory that preserves any data in memory even if the device loses power. Nonvolatile memory is often used for operating systems and long-term data storage.

operating cycle

A sequence of events that the CPU performs according to its program. The operating cycle repeats continuously as long as the CPU is in run mode.

operating modes

A setting that determines the actions of a CPU. Operating modes allow a CPU to accept program instructions or run a program.

Operating system

OS. The software on a computer that allows files to be created and organized, manages the interaction of different programs, holds data in memory, and performs other functions. Operating systems are used on more advanced PLC CPUs.

output devices

A type of field device connected to a PLC that performs a desired action after receiving an electrical signal from the output module. Output devices include components such as motor starters, heaters, and solenoids.

output modules

The portion of a PLC that sends signals to output devices. The output module increases the outgoing signal voltage.

output signals

An electrical signal that the CPU sends to an output module. Output signals cause an output device to turn on or off.

PC

Personal computer. A processor-driven device that runs multiple programs and processes simultaneously. PCs are used as programming devices for PLCs.

peripheral devices

A component connected to a PLC that allows operators to interact with and monitor programs in the PLC. Peripheral devices include programming devices and HMIs.

Personal computer

PC. A processor-driven device that runs multiple programs and processes simultaneously. Personal computers are used as programming devices for PLCs.

Personal protective equipment

PPE. Any clothing or device worn to minimize exposure to hazards and prevent injury. Personal protective equipment for electrical work may include insulated hard hats, insulated gloves, and eye protection.

PLCs

Programmable logic controllers. A processor-driven device that uses logic-based software to control machines and processes. PLCs are used in industrial automation.

power supply

The PLC component that provides electrical energy to the rest of the system. The power supply converts incoming electricity into low-voltage direct current for the CPU and input/output modules.

pressure transducers

A device that converts variations in pressure into an electrical signal. Pressure transducers are a type of analog input device.

preventative maintenance

Regularly scheduled service and upkeep performed while a machine or system is still in working order. Preventative maintenance can prolong equipment life and reduce costs.

Process of elimination

A logical method of removing incorrect options until only the correct option is left. Processes of elimination are used to create and test hypotheses for troubleshooting.

PROFINET

A network communication protocol used for industrial systems. PROFINET uses Ethernet cables for transmission.

program mode

A CPU operating mode in which the CPU does not run a program or perform the operating cycle. Program mode, also known as stop mode, allows operators to change or edit programs.

programmable logic controller

PLC. A processor-driven device that uses logic-based software to control machines and processes. Programmable logic controllers are used in industrial automation.

programming device

A peripheral device used to enter a program into a CPU's memory. Programming devices include personal computers and tablets.

Programs

The set of instructions entered into a CPU's memory that direct the PLC to control field devices. Programs for PLCs are often written in ladder logic.

proportional hydraulic valves

A control valve used in fluid systems that can change its output in response to an input value. A proportional hydraulic valve is a type of analog output device.

Proprietary

Designed by a specific company for use only with its own systems or devices. Proprietary components include hardware like programming devices and software like network communication protocols.

Protocols

A set of standards and rules used by networked devices to interact with each other. Protocols are the language that networked devices use to communicate.

proximity sensors

A device that uses an electronic sensing field to detect the presence of an object. Proximity sensors are common discrete input devices.

pushbuttons

A control device that turns an electrical circuit on or off. Pushbuttons are common discrete input devices.

Rack

An enclosure with slots used to connect multiple parts of a modular PLC. A rack allows some PLC components to share a power source.

Random access memory

RAM. A type of temporary memory storage that allows data to be immediately stored, accessed, and changed. Random access memory is lost in the event that power is removed.

Read-only memory

ROM. A type of memory storage that permanently stores data that can be read but not changed. Read-only memory can be used to store permanent PLC programs.

Relays

A switch controlled by electrical current. Relays are common discrete output devices.

remote run mode

A CPU operating mode in which the CPU executes its program but can be accessed from a programming device. In remote run mode, operators can remotely change the CPU operating mode.

RS-232

A serial interface standard specified by the Electronic Industry Association for the interconnection of devices. RS-232 is the most common type of serial port on PLCs.

run mode

A CPU operating mode that causes the CPU to execute the steps of a program. During run mode, changes cannot be made to a program.

serial communication

A type of communication that transmits and receives data one bit at a time using one signal line to transmit and another signal line to receive. Serial communication is the most basic form of communication used by PLCs.

serial ports

A socket or opening on a CPU that accepts cable connectors with variable numbers of pins. A serial port allows data to be transmitted one bit at a time.

shielded twisted pair cables

A type of twisted pair cable that includes a layer of metal shielding between the intertwined wires and the protective outer jacket. Shielded twisted pair cable is used for network communications.

Smartphones

A small mobile device that functions as both a phone and a computer. Smartphones are able to connect to and send data across the internet.

Software

The programs and instructions that control a computer's hardware functions and operations. Software is written in a programming language.

software key

A number or code used as a password to access functions on a CPU. Software keys are required to access the CPUs of PLCs made by some manufacturers.

Solenoids

A device that converts electrical energy into linear mechanical force. Solenoids are common discrete output devices.

stand-alone devices

A computer or other device that is not connected to a communications network. A stand-alone device can perform its function without requiring additional devices.

Status LEDs

A light made of a semiconductive material that flashes different colors to provide information about a CPU or other PLC modules. Status LEDs indicate conditions such as the CPU's operating mode, network communication, or field device status.

Stop mode

A CPU operating mode in which the CPU does not run a program or perform the operating cycle. Stop mode, also known as program mode, allows operators to change or edit programs.

Tablets

A flat rectangular handheld computer that is usually controlled by a touchscreen. Tablets are mobile devices that allow users to access information from any location.

Temperature sensors

A type of sensor that measures thermal values. Temperature sensors are a type of analog input device.

terminal blocks

An electrical connector on an I/O module where multiple wires are clamped down in I/O points. Terminal blocks are interchangeable and may be moved between modules.

test mode

An operating mode that allows a CPU to run a program without energizing output devices. Test mode may be used to check for program errors.

Touchscreens

A display screen that is designed to respond to the touch and movement of an operator's fingers. Touchscreens are common HMI input devices.

Ultraviolet

UV. Invisible rays of light energy that consist of wavelengths shorter than those of visible violet light. Ultraviolet light is used to erase some types of computer memory.

USB ports

A socket or opening on a CPU that accepts a rectangular USB connector. USB ports are used to connect programming devices and upload programs.

variable frequency drives

VFDs. A device that converts incoming AC power to different frequencies to allow for AC motor speed control. A variable frequency drive is a type of analog output device.

Ventilation

The process of letting in fresh air. Ventilation in a PLC enclosure prevents overheating and dust accumulation.

Volatile

A type of computer memory that does not preserve data in the event of a power outage. Volatile memory includes random access memory.

voltage

The electrical pressure or potential that pushes electrons through a conductor. Voltage is measured in volts (V) and is also called electromotive force.

Volts

V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. Volts measure voltage, which is also known as electromotive force.

wireless local area network

WLAN. A network that enables wireless communication between devices in a single geographic location. Wireless local area networks are typically established by connecting a wireless access point to a wired internet device.

Wireless network

A type of digital communication network that sends and receives signals using radio waves instead of copper or fiber optic cable. In a wireless network, a device transmits a radio signal through an antenna.

wireless router

A networking device that transmits data through an antenna rather than a network cable. Wireless routers, which are used to create computer networks, operate through the use of radio waves.