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Industrial I/O and Fieldbus FAQs

Industrial I/O connects computers to sensors, actuators and controllers. These FAQs cover Modbus, CAN bus, RS-232, RS-422 and RS-485, digital and analog I/O, data acquisition, PLCs, HMIs and SCADA.

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Topics 12
DATA ACQUISITION · SIGNALS AND I/O

Analog vs Digital Signals: What Is the Difference?

An analog signal varies continuously and can take any value in a range, like a 4–20 mA sensor reading or an audio waveform. A digital signal has fixed levels, usually two, representing 1 and 0. Computers work digitally, so analog signals are measured through an analogue-to-digital converter, while on/off signals connect through digital I/O.

6 MIN
AUTOMATION · CONTROL SYSTEMS

What Is Industrial Automation?

Industrial automation is the use of control systems, such as PLCs, robots, sensors and industrial computers, to run machines and processes with little manual work. It covers everything from a single packing machine to a whole plant, and is organized in layers from field devices and controllers up to supervisory, operations and business systems.

6 MIN
GRID · SWITCHGEAR

What Is a Recloser?

A recloser is an automatic circuit breaker used on overhead power lines. When it detects a fault it trips, waits briefly and closes again, because many faults, such as a branch brushing the line, clear on their own. If the fault is still there after a set number of attempts, it stays open and isolates that section.

6 MIN
GRID · AUTOMATION

What Is Feeder Automation?

Feeder automation is the use of sensors, remote-controlled switches and controllers along an electricity distribution feeder to monitor it and respond to problems automatically. It lets a network operator detect faults, reconfigure the feeder and balance load without sending crews to operate switches by hand.

6 MIN
INDUSTRIAL PROTOCOLS · MACHINE TOOLS

What Is MTConnect?

MTConnect is an open, royalty-free standard for reading data from CNC machine tools and other manufacturing equipment. An agent publishes each machine’s state, program, spindle, axis and alarm data as XML or JSON over HTTP, using a common vocabulary, so monitoring software can read different brands of machine the same way.

6 MIN
MANUFACTURING DATA · PRODUCTIVITY

What Is OEE?

OEE (overall equipment effectiveness) measures how much of a machine’s planned production time is truly productive. It multiplies three factors, availability, performance and quality, into one percentage. 100% means making only good parts, as fast as possible, with no stops; around 85% is the benchmark often quoted for leading plants.

6 MIN
MANUFACTURING DATA · INDUSTRIAL I/O

What Is Machine Monitoring?

Machine monitoring is the automatic collection of real-time data from production machines, such as whether each one is running, idle or stopped, its cycle and part counts, alarms and downtime reasons. It shows where capacity is lost and is the usual data source for utilization and OEE reporting.

6 MIN
INDUSTRIAL PROTOCOLS · IIOT

What Is Sparkplug B?

Sparkplug B is an open specification that defines how industrial devices and applications use MQTT. It fixes the topic structure, encodes data as typed, time-stamped metrics using Protocol Buffers, and adds birth and death messages so a SCADA or IIoT host always knows which devices are online and whether their data is current.

4 MIN
INDUSTRIAL PROTOCOLS · GATEWAYS

What Is a Modbus Gateway?

A Modbus gateway converts between Modbus RTU or ASCII on a serial line, usually RS-485, and Modbus TCP on Ethernet. It lets a SCADA system, PLC or edge computer on the network read and write serial meters, drives and controllers as if they were Modbus TCP devices, using the address byte in each request to reach the right device.

6 MIN
SERIAL COMMUNICATION · INTERFACES

What Is Baud Rate?

Baud rate is the number of signal changes, or symbols, a communication link sends per second. On RS-232, RS-485 and other UART serial links each symbol carries one bit, so 9600 baud means 9,600 bits per second. Both ends must use the same baud rate, or the data arrives garbled.

6 MIN
INDUSTRIAL PROTOCOLS · SCADA AND TELEMETRY

What Is DNP3?

DNP3 (Distributed Network Protocol 3) is an open SCADA protocol, standardized as IEEE 1815, that links a control centre master to outstations such as RTUs and protection relays. It runs over serial lines or TCP/IP, reports changes as time-stamped events, lets outstations send unsolicited reports and is widely used by electricity and water utilities.

6 MIN
INDUSTRIAL PROTOCOLS · POWER UTILITIES

What Is IEC 61850?

IEC 61850 is the international standard for communication in electrical substations and other power utility automation. It gives every protection relay, meter and controller a common data model, a configuration language (SCL) and three Ethernet services: MMS for SCADA, GOOSE for fast peer-to-peer trips and Sampled Values for digitized measurements.

6 MIN
INDUSTRIAL I/O · NETWORKS

What Is Fieldbus?

Fieldbus is the family of industrial digital networks that connect controllers such as PLCs to field devices: sensors, actuators, drives and valves. One shared cable replaces a separate wire pair per signal. PROFIBUS, Foundation Fieldbus, Modbus RTU, CANopen and DeviceNet are fieldbuses, standardized internationally in IEC 61158 and IEC 61784.

7 MIN
INDUSTRIAL I/O · MEASUREMENT

What Is Signal Conditioning?

Signal conditioning is the processing that prepares a sensor’s raw signal for measurement. It amplifies or attenuates the signal, filters out noise, isolates it from ground faults, powers or excites the sensor and scales the output to match the input range of an analogue-to-digital converter or control system.

6 MIN
INDUSTRIAL I/O · MEASUREMENT

What Is a Data Acquisition System?

A data acquisition (DAQ) system measures real-world signals such as voltage, current, temperature, pressure or vibration and turns them into digital data a computer can store, display and analyze. It combines sensors, signal conditioning, an analogue-to-digital converter and a computer running acquisition software.

6 MIN
INDUSTRIAL AUTOMATION · IIOT

What Is Smart Manufacturing?

Smart manufacturing is the use of connected machines, sensors, software and AI to monitor production as it happens and adjust it automatically. Data from the shop floor flows to edge computers and business systems, which spot faults, predict failures, check quality and balance output against demand, so factories respond faster with less waste.

6 MIN
INDUSTRIAL I/O · POWER

What Is Galvanic Isolation?

Galvanic isolation separates two circuits so that no current can flow directly between them, while power or data still passes across the gap by light, a magnetic field or an electric field. It breaks ground loops, blocks damaging voltages and noise, and protects people and equipment wherever circuits at different potentials have to connect.

6 MIN
INDUSTRIAL I/O · VEHICLE NETWORKS

What Is CAN FD?

CAN FD (CAN with Flexible Data-rate) is the faster version of CAN bus. It carries up to 64 bytes of data per message instead of 8, and switches to a higher bit rate, typically 2 to 5 Mbit/s, for the data part of each frame. It uses the same two-wire bus and is standardized in ISO 11898-1.

6 MIN
NETWORKING · INDUSTRIAL ETHERNET

What Is a Broadcast Storm?

A broadcast storm is a flood of broadcast or multicast frames that builds up until it uses most of a network’s capacity, so normal traffic stops getting through. The usual cause is a switching loop, where frames circle endlessly and multiply. Loop protection such as RSTP and per-port storm control on managed switches prevent or contain it.

6 MIN
NETWORKING · INDUSTRIAL ETHERNET

What Is LLDP (Link Layer Discovery Protocol)?

LLDP (Link Layer Discovery Protocol) is a vendor-neutral Layer 2 protocol, defined in IEEE 802.1AB, that lets a network device advertise its identity and capabilities to the devices directly connected to it. Switches store what they hear in a neighbour table, which management software uses to map the network, find which port a device is on and negotiate PoE power.

5 MIN
NETWORKING · INDUSTRIAL ETHERNET

What Is RSTP (Rapid Spanning Tree Protocol)?

RSTP (Rapid Spanning Tree Protocol) is the faster version of Spanning Tree Protocol, first published as IEEE 802.1w. It keeps redundant Ethernet links loop-free like STP, but neighboring switches negotiate directly instead of waiting on timers, so recovery after a link failure typically takes around a second or less instead of 30 to 50 seconds.

6 MIN
NETWORKING · INDUSTRIAL ETHERNET

What Is Spanning Tree Protocol (STP)?

Spanning Tree Protocol (STP) is a Layer 2 network protocol, defined in IEEE 802.1D, that stops loops in Ethernet networks with redundant links. Switches elect a root bridge, work out the lowest-cost path to it and block every other path, then unblock a backup link if the active one fails.

8 MIN
INDUSTRIAL PROTOCOLS · INDUSTRIAL ETHERNET

What Is EtherNet/IP?

EtherNet/IP (Ethernet Industrial Protocol) is an industrial network protocol that carries the Common Industrial Protocol (CIP) over standard Ethernet and TCP/IP. Managed by ODVA, it links PLCs, remote I/O, drives and HMIs, using TCP for configuration and UDP for real-time I/O. The IP means Industrial Protocol, not Internet Protocol.

6 MIN
INDUSTRIAL I/O · ANALOGUE SIGNALS

What Is a 4–20 mA Current Loop?

4–20 mA is the standard analog signal for sending a measurement from a field instrument to a controller as a DC current. 4 mA represents the bottom of the range and 20 mA the top, so a broken wire reads 0 mA and is easy to spot. Current is unaffected by cable resistance, so loops run reliably over long distances.

6 MIN
INDUSTRIAL I/O · CONTROL SIGNALS

What Is PWM (Pulse Width Modulation)?

PWM (pulse width modulation) controls the power delivered to a load by switching a digital output fully on and off at a fixed frequency and varying the on-time, called the duty cycle. The load responds to the average, so PWM can set motor speed, LED brightness, valve position or heater output efficiently.

6 MIN
INDUSTRIAL PROTOCOLS · IIOT

What Is OPC UA?

OPC UA (OPC Unified Architecture) is an open standard, IEC 62541, for exchanging data securely between industrial machines, controllers and software on any operating system. Servers publish a browsable information model that describes what each value means, and clients read, write or subscribe to it, with certificates and encryption built in.

6 MIN
INDUSTRIAL I/O · CONTROL SYSTEMS

What Is Remote I/O?

Remote I/O is input and output hardware installed near the sensors and actuators it serves and connected to the controller over a network or fieldbus, rather than wired back to the controller’s own rack. It cuts field wiring on large machines and sites, and it works with PLCs, industrial PCs and gateways.

6 MIN
INDUSTRIAL I/O · SENSORS

NPN vs PNP: What Is the Difference?

NPN and PNP are the two output types of a three-wire DC sensor. A PNP (sourcing) output switches +24 V to the load, so current flows out of the sensor. An NPN (sinking) output switches the load to 0 V, so current flows into the sensor. Each must be wired to an input of the opposite type.

6 MIN
NETWORKING · PORTS AND PROTOCOLS

What Is a TCP Port?

A TCP port is a 16-bit number, from 0 to 65535, that tells a device which application a TCP connection is for. The IP address finds the device and the port finds the service: Modbus TCP listens on 502, OPC UA on 4840 and HTTPS on 443. UDP has its own separate set of port numbers.

7 MIN
NETWORKING · TRANSPORT PROTOCOLS

TCP vs UDP: What Is the Difference?

TCP is connection-oriented: it sets up a session, numbers every byte, resends anything lost and delivers data in order. UDP is connectionless: it sends independent datagrams with no handshake, retransmission or ordering, so it has less overhead and lower latency. Use TCP when every byte must arrive, and UDP when late data is worthless.

7 MIN
INDUSTRIAL AUTOMATION · CONTROL SYSTEMS

What Is SCADA?

SCADA (supervisory control and data acquisition) is a control system that gathers data from PLCs, RTUs and sensors across a plant or a wide area, shows it to operators, raises alarms, logs history and lets staff send commands back to the equipment. Water, power, oil and gas, rail and factories use it to supervise processes they cannot watch by hand.

7 MIN
INDUSTRIAL IOT · CONNECTED OPERATIONS

What Is the Industrial Internet of Things (IIoT)?

The industrial internet of things (IIoT) is the use of connected sensors, machines and controllers in industry, linked through gateways and networks to software that stores and analyses their data. It lets factories, utilities, transport and energy sites monitor equipment remotely, predict failures, cut energy use and improve quality without someone reading each gauge.

7 MIN
INDUSTRIAL AUTOMATION · CONTROLLERS

What Is a PLC?

A PLC (programmable logic controller) is a rugged industrial computer that controls machines and processes. It reads inputs from sensors and switches, runs a control program in a fast repeating cycle and switches outputs such as motors, valves and lamps. PLCs replaced hard-wired relay panels and now run most factory, utility and building automation.

11 MIN
INTERFACES · MILITARY DATA BUS

What Is MIL-STD-1553?

MIL-STD-1553 is a US military standard for a serial data bus that links avionics and vehicle subsystems. It runs at 1 Mbit/s over a dual-redundant shielded twisted pair, and a bus controller commands up to 31 remote terminals. The 1553B revision is used on military aircraft, helicopters, ground vehicles, ships and spacecraft.

7 MIN
INTERFACES · AVIONICS DATA BUS

What Is ARINC 429?

ARINC 429 is the data bus most commercial aircraft use to pass data between avionics. One transmitter sends 32-bit words over a shielded twisted pair to up to 20 receivers, at 100 kbit/s (high speed) or 12 to 14.5 kbit/s (low speed). It is defined by ARINC Specification 429, now maintained by the AEEC under SAE ITC.

7 MIN
INDUSTRIAL IOT · CONTROL

What Is an IoT Controller?

An IoT controller is a networked device that reads sensors, runs control logic and switches outputs on site, while sending data to and taking commands from a remote server or cloud platform. It combines the job of a small controller with IoT connectivity such as MQTT, Modbus TCP, cellular or LoRaWAN.

6 MIN
CONNECTORS · SERIAL I/O

What Is a DB9 Connector?

A DB9 connector is the nine-pin, D-shaped connector used for RS-232 serial ports on computers and industrial equipment. Its correct name is DE-9, because the nine pins sit in the smaller E-size shell. The same connector also carries RS-422, RS-485 and CAN bus, so the pinout depends on the interface behind it.

6 MIN
INTERFACES · SERIAL AND COM PORTS

What Is a Serial Port?

A serial port is a computer interface that sends data one bit at a time over a single line in each direction. On PCs it usually means an RS-232 COM port on a nine-pin connector, and industrial computers also offer RS-422 and RS-485 serial ports for PLCs, sensors and instruments.

7 MIN
GRID · AUTOMATION

What Is FLISR?

FLISR stands for fault location, isolation and service restoration. It is a distribution automation function that finds a fault on a power line, opens switches either side of it to isolate the damaged section, and closes other switches to restore supply to as many customers as possible, often within minutes and without a crew on site.

6 MIN
SCADA · GRID

What Is a Remote Terminal Unit (RTU)?

A remote terminal unit, or RTU, is a field device that connects equipment such as switchgear, pumps or meters to a SCADA system. It reads sensors and status signals, sends the data to a control room over radio, cellular or fiber, and carries out commands sent back, such as opening or closing a switch.

6 MIN
CAN BUS · LINUX

What Is SocketCAN?

SocketCAN is the CAN bus support built into the Linux kernel. It treats each CAN interface as a network device, so software can send and receive CAN messages through standard sockets, and common tools such as candump and cansend work with any supported CAN adapter or onboard CAN port.

6 MIN
IIOT · MONITORING

What Is a Remote Monitoring System?

A remote monitoring system collects data from equipment or environments at distant sites and makes it available centrally. Sensors feed an edge computer or gateway, which processes the readings and sends them over cellular, radio or wired links to a dashboard that shows live status, raises alerts and stores history, so problems are found without a site visit.

6 MIN
PROTOCOLS · FIELDBUS

What Is CAN Bus?

CAN bus (Controller Area Network) is a two-wire network that lets controllers, sensors and actuators share short messages without a central computer. Developed by Bosch for vehicles, it uses a noise-resistant differential signal and gives every message a priority, so critical data gets through first. It is now standard in vehicles, machinery and remote equipment.

6 MIN
EMBEDDED · I/O

What Is GPIO?

GPIO (general-purpose input/output) pins are digital signal lines that software can set as inputs or outputs. As inputs they read on/off signals such as buttons, switches or sensors; as outputs they can drive LEDs, trigger cameras or switch relays through a driver. Embedded boards use them to connect simple signals without a dedicated interface.

6 MIN
FOOD SAFETY · MONITORING

What Is Cold Chain Monitoring?

Cold chain monitoring tracks the temperature of chilled and frozen goods, such as food and medicines, as they are stored, transported and displayed. Sensors record conditions continuously, and a monitoring system raises an alarm when a reading goes out of range and keeps a record that shows the goods stayed safe all the way to the shelf.

6 MIN
IIOT · MONITORING

What Is Remote Temperature Monitoring?

Remote temperature monitoring uses sensors connected to a gateway or controller that sends readings to a dashboard, so temperatures can be watched from anywhere. When a reading moves outside its limits, the system sends an alert, and every reading is logged. It is widely used for fridges and freezers, cold stores, pharmacies, laboratories, server rooms and plant.

6 MIN
PROTOCOLS · COMPARISON

Modbus RTU vs Modbus TCP: What Is the Difference?

Modbus RTU and Modbus TCP carry the same Modbus messages over different links. Modbus RTU sends compact binary frames over serial lines, usually RS-485, with a CRC checksum on each frame. Modbus TCP wraps the messages in TCP/IP packets over Ethernet, normally on port 502. Gateways translate between them so serial devices can join Ethernet networks.

6 MIN
SERIAL · BASICS

What Is RS-232?

RS-232 is a long-established serial communication standard that connects two devices, sending data one bit at a time over separate transmit and receive lines. It is simple and widely supported, usually through a 9-pin D-sub (DB9) connector, and is still common on industrial computers for instruments, scales, PLCs and legacy equipment.

6 MIN
SERIAL · BASICS

What Is RS-422?

RS-422 is a serial communication standard that sends data as a differential signal over twisted pairs, so it resists noise and can run up to about 1,200 m. One transmitter can drive up to ten receivers, and with separate pairs for sending and receiving it works full duplex. It suits long point-to-point links in industrial plants.

6 MIN
SERIAL · COMPARISON

RS-232 vs RS-485: What Is the Difference?

RS-232 is a single-ended serial link between two devices over a short cable, typically up to about 15 m. RS-485 sends a differential signal over a twisted pair, so it resists electrical noise, runs up to about 1,200 m and lets many devices share one bus. RS-422 sits between them: differential, long distance, one sender to several receivers.

6 MIN
SERIAL · BASICS

What Is RS-485?

RS-485 is a serial communication standard that sends data as a differential signal over a twisted pair. That makes it resistant to electrical noise and able to run long cables, up to about 1,200 m, with many devices sharing one bus. It is widely used for industrial control, Modbus RTU, building systems and PTZ camera control.

9 MIN
IIOT · CONNECTIVITY

What Is an IIoT Gateway?

An IIoT (Industrial Internet of Things) gateway is a rugged edge computer that connects industrial equipment, such as PLCs, sensors, meters and machines, to a network or the cloud. It collects their data, translates between industrial and IT protocols, processes and secures it at the edge, and forwards the results.

6 MIN
IIOT · MAINTENANCE

What Is Condition Monitoring?

Condition monitoring is measuring a machine’s health continuously or at regular intervals, using parameters such as vibration, temperature, oil quality, sound and electrical current, to detect changes that point to a developing fault. It turns breakdowns into planned repairs and is the data foundation that predictive maintenance is built on.

6 MIN
PANEL PCS · HMI

What Does HMI Mean?

HMI stands for human-machine interface: the screen, software and controls through which a person monitors and operates a machine or process. In industry, an HMI is usually a touch screen panel PC or operator panel connected to a PLC, showing live values, alarms and controls for a machine, line or plant.

8 MIN
PANEL PCS · HMI

What Is the Difference Between HMI and SCADA?

An HMI is the operator screen for one machine or process. SCADA (supervisory control and data acquisition) is a system that gathers data from many PLCs and sites, stores history, manages alarms and lets operators supervise a whole plant or network. SCADA includes HMI screens, but an HMI does not need SCADA.

6 MIN
PANEL PCS · HMI

How Does an HMI Work With a PLC?

A PLC runs a machine’s control logic; the HMI is the screen operators use to see and change it. The HMI connects to the PLC over an industrial network, usually Ethernet with Modbus TCP, EtherNet/IP, PROFINET or OPC UA, or over RS-485 serial, reading values and writing setpoints and commands back.

6 MIN
EDGE AI · UAV & DRONES

How Does a Jetson Connect to a Flight Controller?

An NVIDIA Jetson connects to a drone flight controller such as a Pixhawk over a serial UART or Ethernet, and sometimes CAN, usually speaking MAVLink. The Jetson runs the AI and autonomy as the companion computer and sends commands, waypoints and position estimates; the flight controller flies the aircraft and returns telemetry.

6 MIN
PROTOCOLS · BASICS

What Is Modbus?

Modbus is an open communication protocol that lets industrial devices such as PLCs, sensors, meters, drives and HMIs exchange data. First published by Modicon in 1979, it uses a simple request and response model: one device asks for or writes values, and another replies. It runs over serial lines as Modbus RTU and over Ethernet as Modbus TCP.

6 MIN
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