Glossary of Industry Standard Terms

Included below is a list of terms frequently used in electrical, automation, and related industries.

AC (Alternating Current): Current that periodically reverses direction.

Ambient Temperature: The temperature of the medium (air, water, etc.) surrounding a device.

Ampacity: The continuous current rating in amperes for a conductor.

Amp (Ampere): The basic unit for current. An ampere, also called an amp, is equal to a current of 1 Coulomb per second. The symbol for ampere is “A.”

Analog: A value that is continuously variable. Also used to describe circuits that work with analog signals.

ATEX: The ATEX directive consists of two EU directives describing what equipment and work environment is allowed in an environment with an explosive atmosphere.

ATEX 95: equipment directive 94/9/EC, Equipment and protective systems intended for use in potentially explosive atmospheres;

ATEX 137: workplace directive 99/92/EC, Minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres.”

AWG (American Wire Gauge): “A common method of specifying wire size (cross-sectional area). Larger numbers represent smaller wires. After AWG No. 1, the largest sizes are AWG No. 0, AWG No. 00, AWG No. 000, and AWG 0000. AWG No. 0 is called one-aught, AWG No. 00 is called two-aught, etc.

Bit: A 1 or 0 representing one position in a binary number. Branch Circuit: A part of a power distribution system extending beyond the final overcurrent protection device.

Byte: Eight consecutive bits.

C1D2 (Class I, Div. 2): Where ignitable concentrations of flammable gases, vapors, or liquids are present within the atmosphere under abnormal operating conditions.

Capacitance: The property of a circuit or device that allows it to store an electrical charge. The symbol for capacitance is “C.” The unit for capacitance is the fared.

Coil: An electromagnetic coil that when energized, closes or opens an electric contact.

Coil Voltage: The voltage required to energize the coil to make or break the contacts of a relay.

Constant Torque: The torque required to keep the load running is the same throughout the speed range.

Contactor: A device with large contacts that close when current is applied to its electromagnet. They are generally used to control the power applied to motors, lights or heating components.

CPT (Control Power Transformer): Coils of wire wound on a common frame that allow electrical energy to be transferred from one circuit to another.

CPU (Central Processor Unit): The decision-making part of a computer / PLC system. It may also be used to describe the processing circuits together with memory and other circuits needed for processing information.

Cracking Pressure: The point at which the internal pressure of a hydraulic system triggers or actuates a valve. Also called the blow-off pressure.

CSA (Canadian Standards Association): A standards-defining organization founded in 1919. It is involved in many industries, including electronics, communications and information technology.

Current: The flow of electrons in a circuit. Current is designated by the symbol “I” and is measured in amperes.

Cv Factor: A dimensionless coefficient or value which indicates relative flow capacity of a valve, defined as the gallons of water per minute (USGPM) at 60° F, which will flow through the valve at a one (1) PSIG pressure drop.

Digital: Used to describe circuits that use on or off (binary) signals. Also used to describe equipment that includes these circuits.

DC (Direct Current): Current in a constant direction.

Distributed I/O: Uses a network of sensors, transmitters, transducers, and monitoring devices to control a distributed system.

Ethernet: A system for connecting a number of computer systems to form a local area network, with protocols to control the passing of information and to avoid simultaneous transmission by two or more systems.

Explosion Proof: A motor enclosure type used in hazardous locations. Explosion-proof enclosures are also available for other types of equipment.

FM (Factory Mutual) Approvals: North American insurance company that provides certification of industrial and commercial products.

FNPT: Female National Pipe Thread (See NPT)

Frequency: The rate of variation of a periodic waveform. The symbol for frequency is “f.” The unit for frequency is Hertz.

Ground: A connection to the earth or to a conductive object such as an equipment chassis.

HART Fieldbus: A network system whereby instruments (measuring flow, level, temp,etc..) communicate to the main automation station using SMART technology.

Heat Dissipation: Dissipation of Heat

Hz (Hertz): A unit of frequency equal to one cycle per second. Hertz is abbreviated Hz.

HMI (Human Machine Interface): A device or software that lets users communicate with a machine or automation system. Besides translating complex data into useable information, an HMI relays the user’s commands.

HP (Horsepower): A unit of power. Horsepower is abbreviated HP. 1 horsepower is equal to 746 watts.

IEC (International Electrotechnical Commission): An organization based in Geneva, Switzerland with over 50 national committees as full members. ANSI represents the U. S. IEC writes international standards for electrical and electronic technologies and practices.

Impedance: The total opposition to alternating current. Impedance is the vector sum of resistance and reactance. The symbol for impedance is “Z.” The unit for impedance is the ohm.

H2 O (Inches of water): a unit of measure for quantity of water, being the quantity which will flow through an orifice one-inch square, or a circular orifice one inch in diameter, in a vertical surface, under a stated constant head; also called miner’s inch and water inch. The shape of the orifice and the head vary in different localities. In the Western United States, for hydraulic mining, the standard aperture is square and the head from 4 to 9 inches above its center. In Europe, for experimental hydraulics, the orifice is usually round and the head from 1/2 of an inch to 1 inch above its top.

Inductance: The property of an electrical circuit that opposes changes in current. Inductance is designated by the symbol “L” and is measured in henries.

Inrush Coil Power Consumption: The amount of power consumed to activate the coil of a contactor when first turning on a motor

Interrupting Rating: The maximum amount of current a protective device can cut off without harm to personnel or resulting damage to equipment, the premises or the device itself.

LBM: Lower Back Mount

Line: Line is the power coming in or “upstream”.

Load: Load is the power going out “downstream” of the device that interrupts power.

Loop Power: A 4-20ma loop-powered device extracts the power it needs to run its circuits from the loop itself. There is no separate power feed from the Analog input card or from anywhere else. The current that the device draws becomes part of the 4 to 20 ma. that flows in the loop, therefore the device must not require more than 4ma to operate.

MCM: Abbreviation for a thousand circular mils. Circular mills are used to designate the cross-sectional area of a round conductor. One mill is equal to 1/1000 of an inch. The circular mill area of a solid, round conductor is calculated by squaring the conductor’s diameter (in mills). 1 MCM is 1000 circular mils (also shown as 1 kcmil).

MNPT: Male National Pipe Thread (See NPT)

Modbus: Modbus is a serial communications protocol published by Modicon in 1979 for use with its programmable logic controllers (PLCs). It has become a de facto standard communications protocol in industry and is now the most commonly available means of connecting industrial electronic devices.

Motor Starter: A contactor and an overload relay assembled together to remotely control the operation of a motor while providing overload protection.

MTW: Machine Tool Wire is a type of wire whose insulation is made to be flexible for use in machines experiencing significant motion or vibration.

NACE (National Association of Corrosion Engineers): The leader in the corrosion engineering and science community, and is recognized around the world as the premier authority for corrosion control solutions.

NC Contact: Normally Closed contact – is closed in its de-energized (off) state and opens the contact when energized.

NEC (National Electrical Code): A document revised every three years based upon inputs to and recommendations of volunteer committee members of the National Fire Protection Association. The intent of the NEC ®, also called NFPA 70®, is to describe safe electrical practices. Although the NEC® is an advisory document, its use is often mandated by state and local building codes.

NEMA (National Electrical Manufacturers Association): An organization of manufacturers of electrical equipment that, among other things, develops standards for electrical equipment.

NO Contact: Normally Open contact – is open in its de-energized (off) state, and closes the contact when energized.

NPT (National Pipe Thread): Tapered Thread is a U.S. standard for tapered threads used on threaded pipes and fittings. The taper rate for all NPT threads is 1⁄16 (3⁄4 inch per foot) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe is 1° 47′ 24″ (1.7899°).

Ohm: The basic unit of resistance, reactance and impedance. The symbol for the ohm is “Ω”, the Greek letter omega.

OPC: The acronym “OPC” comes from “OLE (Object Linking and Embedding) for Process Control. OPC is a software interface standard that allows Windows programs to communicate with industrial hardware devices.

Overload: Can refer to an operating condition in excess of the full-load rating or a current high enough to cause damage if it is present long enough. Short circuits and ground faults are not overloads. Parallel Circuit: A closed circuit in which the current divides into two or more paths before recombining to complete the circuit

PDM: Product data management is the use of software or other tools to track and control data related to a particular product.

PID Controller: A proportional–integral–derivative controller (PID controller) is a generic control loop feedback mechanism (controller) widely used in industrial control systems – a PID is the most commonly used feedback controller. A PID controller calculates an “error” value as the difference between a measured process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process control inputs.

Pilot Device: Pilot devices are a family of related products including pushbuttons, selector switches, pilot lights, toggle switches, and signal beacons. In its simplest form, a pilot device is basically a device that communicates information, whether it is from the human operator to the machine, or from the machine back to the operator.

PLC (Programmable Logic Controller): A type of industrial computer used to control machines and processes. The PLC accepts inputs from switches and sensors and uses these inputs together with other data and program logic to control output devices.

Power: The rate at which work is done or energy is transformed. In an electric circuit, power is measured in watts, or sometimes in horsepower. The term power is also often used to refer to electrical energy and as an adjective to describe devices or circuits designed to carry a high level of current.

Power Supply: A source for power that converts AC line voltage to the type of power required by a particular device, typically 24 VDC.

Primary Voltage: The voltage applied to the terminals of the primary winding of a transformer.

Profibus: (Process Field Bus) is a standard for field bus communication in automation technology and was first promoted (1989) by BMBF (German department of education and research). It should not be confused with the PROFINET standard for Industrial Ethernet.

PSI: Pounds per square inch. A unit of pressure.

PSIA (PSI Absolute): A pressure reading using vacuum as the reference.

PSIG (PSI Gauge): A pressure reading using ambient air pressure as the reference.

PTFE: Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon.

RAM (Random Access Memory): Usually refers to a type of semiconductor memory often used for temporary storage. RAM requires the continual application of power to retain information. For some systems, battery backup is used to prevent data or program loss in the event of a power outage.

Redundancy: Duplication of critical components of a system with the intention of increasing reliability of the system.

Resistance: A property of a material or circuit that opposes current flow. Resistance is symbolized by “R” and is measured in ohms.

Resolution: Indicates the number of discrete values that can be produced over a range of analog values. The values are usually stored electronically in binary form, so the resolution is usually expressed in bits. The number of discrete values available, or “levels”, is a power of two. For example, an Analog to Digital Converter with a resolution of 8 bits can encode an analog input to one in 256 different levels, since 28 = 256. The values can represent the ranges from 0 to 255 (i.e. unsigned integer) or from −128 to 127 (i.e. signed integer), depending on the application.

ROM (Read Only Memory): Usually refers to a type of semiconductor memory often used for permanent storage of data or programs that do not change.

Sealed Coil Power Consumption: The amount of power consumed to hold the coil of a contactor once it has already been activated. Secondary

Voltage: The voltage supplied by the terminals of the secondary winding of the transformer.

Series: A circuit having its parts connected serially

Short Circuit: A normally unintended low resistance path for current.

SNMP: Simple Network Management Protocol is an “Internet-standard protocol for managing devices on IP networks.

Solid State: Used to describe equipment that contains semiconductor devices in an electronic circuit.

Static Pressure: The pressure exerted by a still liquid or gas, especially water or air.

Surge Current: A short duration, high-amperage electric current wave that may sweep through an electrical network, as a power transmission network, when some portion of it is strongly influenced by the electrical activity of a thunderstorm.

Surge Protection Device: An appliance designed to protect electrical devices from voltage spikes.

TFFN: Thermoplastic Flexible Fixture Wire Nylon which is slightly different than the THHN wire because it has a lower heat resistance and it’s not good for wet locations.

THHN: Thermoplastic High Heat-resistant Nylon coated. THHN can come in stranded or solid conductors depending on the size. It is either manufactured in copper or aluminum and covered in a PVC (polyvinyl chloride) insulation with a nylon jacket.

Torque: A turning or twisting force. Since torque is expressed as a force times the length of the radius at which the force is measured, torque is represented in compound units such as pound-feet (lb.-ft.)

UL (Underwriters Laboratories): An independent product safety certification organization, Underwriters Laboratories, Inc. develops standards and tests products for safety. Products that pass UL tests can carry a UL mark. UL has several categories of marks based upon the type of product tested.

U-Length: Thermowell immersion lengths are often called the “U” length. The U length is the measurement of the Thermowell from the bottom of the process connection to the tip of the Thermowell. The U length establishes the length of the Thermowell that is actually in the process being measured.

USS (Universal Serial Interface): The USS protocol defines an access technique according to the master-slave principle for communications via a serial bus. This also includes, as sub-quantity, the point-to-point connection.

Vacuum: An enclosed space from which matter especially air has been partially removed so that the matter or gas remaining in the space exerts less pressure than the atmosphere.

Variable Torque: Loads have characteristics requiring low torque at low speeds and increasing values of torque required as the speed increases.

Voltage: Also called potential difference, electromotive force, or EMF. Voltage is a force that, when applied to a conductor, causes current to flow. Voltage is symbolized by “E” or “V” and is measured in volts.

Watt: The basic unit of electric power. The symbol for watt is “W.”

Wetted Parts: The diaphragm and pressure port material that comes in direct contact with the medium (gas, liquid).

WOG: Water Oil or Gas Service

Word: Usually one or more bytes used to represent instructions or data in digital equipment.

Hunter Schwedler is an Outside Account Manager for AWC, Inc. in the Houston, TX office. With over 2 years of experience in industrial automation, he has a BS in Electronic Systems Engineering Technology from Texas A&M University.

Hunter Schwedler

Outside Account Manager

Hunter Schwedler

Outside Account Manager

Hunter Schwedler is an Outside Account Manager for AWC, Inc. in the Houston, TX office. With over 2 years of experience in industrial automation, he has a BS in Electronic Systems Engineering Technology from Texas A&M University.
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