PLC Installation Practices 345

alternating current

AC. A current formed when electrons flow in one direction and then the opposite direction. Alternating current may be used by some PLC outputs.

analog signals

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

antistatic packaging

Materials resistant to the build-up of electric charge that cover or protect electronic components. Antistatic packaging should be used for electrically sensitive components of a PLC.

antistatic workstations

A sturdy area or table made of antistatic materials that protects objects on the surface from ESD damage. Antistatic workstations should be used when working with modular PLCs.

antistatic wrist straps

A type of wrist strap that conducts electricity away from the wearer and into the ground. Antistatic wrist straps have a grounding cable that attaches to a grounded workstation.

architecture

The organization, structure, and design of PLC hardware and software. PLC architecture must be designed to meet manufacturing needs.

arc-rated

Safety equipment that is designed to withstand high voltages. Arc-rated PPE reduces the risk of electrocution from arc flashes.

assembly lines

A production process in which products are mass-produced in stages. Assembly lines use programmable logic controllers to help objects pass through different workstations until they are complete.

automation

The automatic control of equipment, a process, or a system. Automation is an efficient means of performing manufacturing processes.

cable ties

A long, thin plastic or nylon fastening device that locks when the point on one end is threaded through the loop on the other. Cable ties, or zip ties, can be used to attach tagout devices.

cable trays

A supportive device that holds wiring and provides ventilation for cables. Cable trays help organize and secure cables.

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.

chassis

An enclosure with slots in it that is used to connect and hold the multiple units of a modular PLC. A chassis, also known as a rack, typically allows room for additional units.

circuit breakers

A device that detects excess current to prevent overheating in a circuit. A circuit breaker often contains a bimetallic strip that bends and trips a switch to open a circuit.

circuitry

A closed path or multiple paths, usually composed of various devices and wires, through which an electric current follows. Circuitry design is important when creating PLCs to ensure they function as desired.

communication protocols

A set of formal rules describing how to transmit or exchange data, especially across a network. Communication protocol standards enable equipment to efficiently communicate with one another.

compact

A type of PLC in which the central processing unit, input/output module, and power supply are housed in a self-contained unit. A compact PLC, also known as a fixed PLC, is used for applications requiring basic process control.

connectors

The part of a wire that plugs into a port in an electronic device. Connectors come in different varieties depending on their purpose.

conveyor belt

A belt used in industry to transport materials over a distance. A conveyor belt may be controlled by a PLC.

corroded

A deteriorated or worn material. Corroded wire harnesses can occur from sunlight, water, oil, or chemicals.

corrosive

A chemical solid, liquid, or gas capable of irreparably harming living tissue or damaging material on contact. Corrosive materials can degrade PLCs.

current

The flow of electricity through a circuit. Current strength is called amperage and is measured in amperes (A), or amps.

cybersecurity

Protection against criminal or unauthorized access to computer networks, programs, and data. Cybersecurity has become a major industrial concern as networking and connectivity have increased.

data recovery

The process of restoring data that has been lost, accidentally deleted, corrupted, or made inaccessible. Data recovery can reduce losses and damage from a cyberthreat.

DC

Direct current. A current formed when electrons flow in a single direction continuously. DC uses sinking or sourcing for PLCs.

debugging

Testing programs to identify and fix errors. Debugging can occur automatically in some PLC programs.

diagnostics

A set of computer instructions for investigating or analyzing the cause or nature of errors or failures in the PLC. Diagnostics will keep a PLC and its programs running correctly.

dielectric

Having little or no ability to conduct electricity. Dielectric materials are used in footwear to prevent electric shock.

digital signals

An electrical impulse that has only two states. Digital signals, also known as discrete signals, are either on or off.

DIN rails

A metal track or rail to which PLCs and other electronic devices can be easily attached or removed. DIN rails are often used in electrical panels, wall boxes, charging stands, and other electrical devices.

direct current

DC. A current formed when electrons flow in a single direction continuously. Direct current uses sinking or sourcing for PLCs.

discrete signals

An electrical impulse that has only two states. Discrete signals, also known as digital signals, are either on or off.

distributed I/O system

A network that uses remote I/O modules and multiple PLCs. Distributed I/O systems may be wired or wireless.

electrical noise

Unwanted changes in the voltage of the current traveling on a wire, caused by another electrical source. Electrical noise is reduced by twisted pair cables and shielding.

electronic data sheet

EDS. A text file that outlines a device's data information for configuring and understanding the capabilities for integration between systems and components. An electronic data sheet can be downloaded from the device manufacturer.

electrostatic discharge

ESD. A release of static electricity that occurs when two charged objects come into contact. Electrostatic discharge is a major concern when working with electronics as it can harm equipment and technicians.

emulation

A PLC test that runs the program on a personal computer as if it were a physical system. Emulation mimics both the software and hardware of a PLC.

engineer

A person who designs machines, parts, or other technically complex components or features. In manufacturing, engineers are responsible for designing programmable logic controllers.

failover support

The ability to continue operation if a component fails. Failover support is essential for some PLC operations.

fail-safe

A response to unsafe conditions that causes systems to resort to non-dangerous states. Fail-safe may involve the closing of machine doors when a safety PLC has failed.

fault codes

The digital information output by a computing device that corresponds to a malfunction in a mechanical or electrical system. Fault codes are used to identify the type of malfunction and help facilitate troubleshooting processes.

field devices

A component that connects to an input/output module on a PLC and performs an action. Field devices have their own electrical requirement.

fixed

A type of PLC in which the central processing unit, input/output module, and power supply are housed in a self-contained unit. A fixed PLC, also known as a compact PLC, is used for applications requiring basic process control.

fuses

A safety device that detects excess current in a circuit. Fuses often have a component that melts and opens the circuit.

grounding bus bar

A metal bar in a PLC enclosure that provides a grounding point for the components of the PLC. A grounding bus bar typically mounts on the back of the PLC panel.

hardware

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

HMIs

Human machine interfaces. A device or system that displays machine or process information. HMIs may have a graphical or textual display.

horizontal

Parallel to the horizon or ground. PLCs should always be mounted horizontally on a surface.

human-machine interfaces

HMIs. A device or system that displays machine or process information. Human-machine interfaces may have a graphical or textual display.

humidity

The amount of water vapor in the air. Humidity control is important for 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. I/O modules may be input only, output only, or a combination.

industrial PLCs

A type of modular PLC that contains all modules in one centralized location. Industrial PLCs, also known as rack-mounted PLCs, are commonly used for conveyor belts.

input/output modules

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

installation guide

A technical document that outlines the specific procedures for mounting, wiring, and configuring a PLC. The installation guide will provide various ways to install the PLC, depending on the operation.

Institute of Electrical and Electronics Engineers

IEEE. An international organization composed of engineers, scientists, and students in the electrical field. The Institute of Electrical and Electronics Engineers sets standards for the electronics and computer industries.

insulated

Covered in a material that prevents the passage of electricity. Insulated gloves, boots, and hard hats are common PPE for electrical work.

internet protocol addresses

IP addresses. A unique numeric identifier for each node on a network. Internet Protocol addresses are used to communicate with a device using an internet protocol.

in-the-loop

A test for PLC programs that physically runs the program on the PLC hardware. In-the-loop testing can reveal timing issues or electrical issues that a simulation alone may not reveal.

IP addresses

Internet protocol addresses. A unique numeric identifier for each node on a network. IP addresses are used to communicate with a device using an internet protocol.

labeling machine

A device that adds labels to products or packages. A labeling machine may use a programmable logic controller to manage precise labeling.

LED indicators

Lights on a PLC that signify different issues or states of the PLC. LED indicator lights can help diagnose a problem with a PLC.

legacy

Relating to a previous technology. Some legacy software may be obsolete, while legacy machines are often still in use.

level

Completely horizontal and in alignment. Level the PLC to ensure it functions properly.

light-emitting diode

LED. A semiconductor transducer that emits a narrow spectrum of light in a forward direction. A light-emitting diode is a passive transducer that transforms electrical signals into light.

local area networks

LANs. A communication network that connects computers and associated devices together over a short or long distance. Local area networks use a wired connection.

local I/O modules

An I/O module located in the same space as the controller. Local I/O modules have high communication speeds.

lockout/tagout

LOTO. A method of protecting employees by preventing accidental machine startup through proper locking and labeling of machines during maintenance. Lockout/tagout is important for installing PLCs.

maintenance

Activities for the necessary care and repair of machines, such as the lubricating, adjusting, and replacement of parts. Maintenance requires time, labor, and money but results in savings.

memory

The portion of a computer where data is stored. Memory storage can be built into the central processing unit of a PLC or contained in a removable device.

memory card

A storage device that allows data to be easily read and easily changed. Memory cards continue to store data if the power source is removed.

milliamperes

mA. A unit of current equal to one thousandth of an ampere. Milliamperes may be used to measure current.

modular PLCs

A type of PLC that has removable and interchangeable units, including the central processing unit, power supply, and input/output modules. A modular PLC can process a larger variety of input/output signal levels to meet the needs of a more complex application.

motion control PLCs

A specialized programmable logic controller designed to control the movement of devices like servomotors. Motion control PLCs are used for CNC machines and pick-and-place robots.

mounting latch

A device located on a PLC that locks it into a DIN rail. The mounting latch can be set to the unlocked or locked position.

multimeter

A device that can measure voltage, current, and resistance. A multimeter is used when verifying the voltage of an input/output device for a PLC.

National Electrical Code

NEC. The standard for minimum safe electrical installations in both residential and commercial settings. The National Electrical Code is adopted in some form as law in all 50 states.

National Electrical Manufacturers Association

NEMA. An organization that sets standards for electrical equipment used in the United States. The National Electrical Manufacturers Association also provides ratings for electrical devices.

network parameters

A set of measurable factors or characteristics that define the scope of data transmission within a PLC system. Network parameters must be defined when wiring PLC communication connections.

noise immunity

The ability of a device to resist electrical interference. Noise immunity is important for programmable logic controllers in large, industrial environments.

NPN transistor

A semiconductor device that consists of a layer of P-type semiconductor material sandwiched between two layers of N-type material. A NPN transistor is used in sinking devices and has fast switching speeds.

orderly system shutdown sequence

A programming code that prevents damage or injury in an emergency by shutting down equipment or devices. Orderly system shutdown sequence protects technicians in case of an emergency.

overloading

A state in which the level of current exceeds the recommended level for a device or circuit. Overloading can cause overheating and equipment damage.

personal computer

PC. A processor-driven device for an individual user with commercial software. A personal computer may be used as a programming device for a PLC.

personal protective equipment

PPE. An article of clothing or a device worn to minimize exposure to hazards and prevent injury. Personal protective equipment for employees working with or around PLCs include clothing that reduces electrostatic discharge.

PLC

Programmable logic controller. A processor-driven device that uses logic-based software to provide electrical control to machines or processes. PLCs are used in factory automation.

PNP transistor

A semiconductor device that consists of a layer of N-type semiconductor material sandwiched between two layers of P-type material. A PNP transistor is used in sourcing devices and is easier to troubleshoot.

polarity

Having a positive or negative charge. Polarity determines the direction in which current flows.

power supply

The component that provides power to the central processing unit and input/output modules on a PLC. The power supply converts incoming current into a lower voltage for the CPU.

processing power

A programmable logic controller's ability to execute programs, perform tasks, and manage scan cycles efficiently. Processing power must be considered when selecting a PLC.

programmable logic controllers

PLCs. A processor-driven device that uses logic-based software to provide electrical control to machines or processes. Programmable logic controllers are used in factory automation.

protective debris strip

A piece of plastic adhered to the top of the PLC that protects the unit's vents during installation. Remove the protective debris strip after installation or else it could cause the PLC to overheat.

proximity sensor

A device that detects a change in a physical condition and turns it into an electrical signal. Proximity sensors are common discrete input devices.

pushbuttons

A type of mechanical contact that controls some aspect of a machine or process. A pushbutton is a common type of discrete input device.

rack

An enclosure with slots in it that is used to connect multiple parts of a modular PLC. A rack, also known as a chassis, typically allows room for additional units.

rack-mounted PLCs

A type of modular PLC that contains all modules in one centralized location. Rack-mounted PLCs, also known as industrial PLCs, are commonly used for conveyor belts.

redundancy

The duplication of controllers and components to have backup in the case of failure. Redundancy includes components that substitute for failing components to avoid having a complete system shutdown.

redundant PLCs

A specialized programmable logic controller that supports the production process in case of failure or stoppage. Redundant PLCs back up operations so that downtime is reduced.

relay contacts

The conductive components in a relay that open or close in response to circuit conditions. Relay contacts are common discrete input devices.

relays

A device that controls one circuit by opening and closing the contacts in another circuit. Relays are common discrete output devices.

remote I/O modules

A I/O module hosted at a location different from the controller. Remote I/O modules offer more flexibility in expanding the network.

root cause analysis

A study to determine the cause of a problem. Root cause analysis involves collecting and analyzing data to find a problem's origin.

safety PLCs

A specialized programmable logic controller that enhances the safety of operations by overseeing the safety of all system operations. Safety PLCs minimize risks by diagnosing and responding to faults.

scalability

The ability to expand a PLC system based on its capacity or without requiring replacement. Scalability is important for larger manufacturers that may expand or grow operations.

screwdriver

A tool used to fasten and tighten screws. Screwdrivers have a handle on one end and a blade on the other that fits into the recess in the head of a corresponding screw.

shielded twisted pair

STP. 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.

shielding

A protective layer in an electrical cable that protects the wires within from electromagnetic interference. Shielding can be made from foil tape, foil wrap, or other metal materials.

signal range

The recommended operating limit for an electronic device. Signal range is important to consider when wiring PLC input/output modules.

simulation

A PLC test that runs the program of a PLC in a virtual space. Simulations allow engineers to test PLC designs.

simulator

A computer program that generates a model of a PLC. Simulators may be used for testing a network or program for a PLC.

sinking

Receiving current from another device in a circuit. A sinking device contains a NPN transistor.

sinking input device

A device that receives current from a sourcing output and connects to the ground of the power supply. A sinking input device may be a PNP proximity sensor.

sinking output device

A device that receives current from the load and connects it to the ground of the power supply. A sinking output device may be a light, solenoid valve, or motor starter.

software

The programs and instructions that a processor-driven device carries out. Software in a PLC replaces many physical components, such as hard-wired relays.

sourcing

Supplying current in a circuit. A sourcing device contains a PNP transistor.

sourcing input device

A device that supplies positive voltage to turn on a device and allows current to flow into the controller. A sourcing input device can be a NPN proximity sensor.

sourcing output device

A device that supplies positive voltage to a load. A sourcing output device may be a light, solenoid valve, or motor starter.

stress tests

Putting a system through intense conditions to determine the breaking point. Stress tests should be performed on PLC communication networks to understand their limitations.

supervisory control and data acquisition

SCADA. A control system architecture used to monitor and control industrial processes. Supervisory control and data acquisition systems can make supervisory decisions locally or remotely.

technical data sheet

A detailed document about a product's specifications, performance, and usage. The technical data sheet for a PLC should be consulted prior to installation.

topologies

The configuration or physical pattern of parts and components within a working system, such as a controller area network. Common topologies include a bus, ring, and star shape.

triodes for alternating current

TRIAC. A complex semiconductor switch that has a four- or five-layer sandwich and three terminals called the gate, Main Terminal 1 (MT1), and Main Terminal 2 (MT2). Triodes for alternating current are designed specifically for AC and are primarily used for high-power and high-voltage applications.

troubleshooting

A systematic approach to solving problems quickly and efficiently. Troubleshooting often involves a logical process of elimination to identify the source of a problem.

underpowering

A state in which the device does not receive enough current to operate. Underpowering a PLC output can cause failure.

V

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

variable frequency drives

VFDs. A device that converts incoming AC power into other desired frequencies to allow for AC motor speed control. A variable frequency drive is a common analog output device for PLCs.

vibration

A rapid, continuous repeated motion in a machine or other structures. Vibration can negatively affect PLCs.

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. The V unit measures voltage, which is also known as electromotive force.

wire gauge

A standard measurement used to describe the diameter of wire. Wire gauge should be selected carefully when assembling a PLC.

wireless

Able to send and receive signals through the air instead of using cable. Wireless PLC networks allow for I/O modules to be located in different spaces.

wiring diagram

An electrical print that shows the physical locations and electrical relationships of all electrical components in a circuit. Wiring diagrams use symbols, like schematic diagrams, but they are much less common.