Industrial automation glossary

All terms

PLC (Programmable Logic Controller)

A rugged industrial computer that reads inputs, runs a control program and switches outputs to control machines and processes.

HMI (Human-Machine Interface)

A screen or panel that lets an operator see the state of a machine and enter commands.

SCADA

Supervisory Control and Data Acquisition: software that collects data from many controllers and shows, logs and controls a plant from one place.

VFD (Variable Frequency Drive)

A power electronics device that controls the speed and torque of an AC motor by changing the output frequency and voltage.

Soft starter

A device that ramps the voltage to a motor for a smooth start and stop, without controlling running speed.

Servo drive

A drive that controls a servo motor in a closed loop using position or speed feedback from an encoder or resolver.

Fieldbus

A digital communication system that connects controllers to field devices such as sensors, drives and I/O modules.

PROFINET

An industrial Ethernet standard, widely used with Siemens controllers, for fast cyclic I/O and diagnostics.

EtherNet/IP

An industrial Ethernet protocol based on the Common Industrial Protocol (CIP), widely used with Rockwell Automation controllers.

Modbus

A simple, open communication protocol that exchanges register data between a master and slave devices over serial lines (RTU) or Ethernet (TCP).

OPC UA

A vendor-neutral, secure industrial communication standard for exchanging structured data between machines and IT systems.

MQTT

A lightweight publish-subscribe messaging protocol used to send data from many devices to a broker.

MES (Manufacturing Execution System)

Software that manages and records production on the shop floor, between the machines and the ERP system.

ERP

Enterprise Resource Planning: business software for orders, inventory, finance and purchasing.

I/O (Input/Output)

The signals a controller reads from sensors (inputs) and writes to actuators (outputs).

PNP / NPN

Two output types for sensors. PNP switches the positive supply to the load; NPN switches the load to ground.

IP rating

A two-digit code that shows how well an enclosure or device is protected against solid objects and water.

STO (Safe Torque Off)

A safety function in a drive that removes the energy that can produce torque, so the motor cannot start unexpectedly.

SIL / Performance Level

Measures of the reliability of a safety function, used to specify how safe a machine safety circuit must be.

MPN (Manufacturer Part Number)

The unique order number a manufacturer gives a product. Matching the full MPN avoids ordering the wrong variant.

MLFB

The machine-readable order number format used on Siemens products.

BOM (Bill of Materials)

A list of the parts, with quantities, needed to build or maintain a machine.

RFQ (Request for Quotation)

A request to a supplier for a written price and delivery quotation for specified parts and quantities.

Obsolescence

The point at which a product is discontinued by the manufacturer and no longer produced or fully supported.

Definitions are general. Always confirm product details in the manufacturer’s datasheet.