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IO-Link FAQs and glossary



What is IO-Link ?

IO-Link is an open, standardised technology that allows the user to set up a point-to-point connection. IO-Link requires no sensor addressing. IO-Link components from companies that are members of the IO-Link consortium are compatible with each other.

Is IO-Link another fieldbus?

IO-Link is no fieldbus. In the automation structure, IO-Link is located below the fieldbus topology. IO-Link masters are used to connect the sensors to the fieldbus and the connected controller (see image).

How can I integrate IO-Link sensors into my controller?

The process data transmitted by the IO-Link sensor can be read by the PLC without further conversion. Read the section System integration for more information.

What does the abbreviation IODD stand for?

IODD is the abbreviation for IO-Link Device Description. An individual IODD file exists for each IO-Link device. The device properties and individual sensor information such as identification, process and diagnostic data are stored here. These are required for integrating the sensor into the IO-Link infrastructure.

ifm provides the IODD file for each IO-Link product on its website under "Documents & downloads". In addition, the IODD of each IO-Link device sold by ifm is saved in the company's parameter setting software and in other software solutions for IO-Link device and port configuration tools from ifm.

The IO-Link community also offers a manufacturer-independent IODD library: To the IODD finder

Transmission of measured values

How do IO-Link sensors transmit measured values?

Via IO-Link, the measured values and process values are transmitted in a purely digital form - without conversions - from the sensor to the PLC.

How does the IO-Link measured value differ from an analogue signal (4…20 mA)?

The entire measured value transmission is digital. There are no conversions of the measured value. With analogue signal transmission, the digitally measured value is converted into an analogue signal in the sensor and transmitted to the PLC, where it is converted back into a digital signal. This transmission principle is prone to errors and conversion losses. For further advantages click here!


Can wire break be detected with IO-Link?

Yes. The IO-Link master checks all IO-Link devices within a communication cycle. If a device does not respond, the wire break is immediately detected and signalled irrespective of the measured value.

Can IO-Link sensors signal malfunctions?

Yes, this is done via events. A sensor (a device) can detect and signal an incorrect operating status to the master. This is done by setting a bit in the interface. The master reads this event and transmits it to the controller as a classic error code.

IO-Link master

What is an IO-Link master?

The IO-Link master establishes the connection between one or several IO-Link devices and the fieldbus system serving as a gateway. Product overview: IO-Link masters

IO-Link master setup

Every master port must be configured by the user according to the requirements of the user's application: master port mode (DI, DO, IO-Link), process data width and data length. Recommendation: Activate the device identification for future compatible replacements. The LR DEVICE software makes this task easier by scanning the network for available IO-Link masters and connected devices.

Upload and download of IO-Link device parameters

Whether a port automatically uploads or downloads depends, on the one hand, on the parameter setting of the IO-Link device and, on the other hand, on the configuration of the master port. The parameter setting of the IO-Link device and the master configuration are carried out using an engineering tool such as LR DEVICE.
LR DEVICE via USB stick: QA0011
LR DEVICE via download: QA0012

Advantages without an existing IO-Link structure

Can I benefit from IO-Link sensors without existing an IO-Link structure?

Generally, an IO-Link sensor also functions without an IO-Link infrastructure. In this case, it acts as a normal sensor, the additional information is not provided. However, if combined with the memory plug, IO-Link sensors can considerably simplify sensor parameter setting. If the system is retrofitted to IO-Link at a later date, all the advantages of IO-Link will be immediately available.

What advantages does the memory plug offer?

For installations without IO-Link the memory plug allows transmission of parameters to replacement units. To do so, it reads and saves the data of a connected IO-Link sensor. The saved parameters can be copied to sensors of the same type with factory setting.
ifm memory plug: E30398



Device that converts electrical signals into kinetic energy.

A port / B port

An A port has an integrated, low-current power supply for devices; a B port allows a second isolated supply for outputs.

Acyclic data

Data that is only transferred from the controller after a request (e.g. parameter data, diagnostic data).

Bidirectional data

Data that goes in both directions (from and to the IO-Link master). Thus, the sensors can be configured and read during running operation.


IO-Link data transfer rates. Up to 32 bits can be transferred between IO-Link device and IO-Link master per cycle. With COM1 they are transmitted at 4.8 kBit/s, with COM2 at 38.4 kBit/s and with COM3 at 230.4 kBit/s.


A device can be a sensor, an actuator or a hybrid device. It is a passive participant and only replies at the master's request.


Digital input / output.


Device Type Manager (manufacturer-specific driver).

I/O configuration of different ports via IO-Link

When using IO-Link the user receives both input and output data via the port of a sensor/actuator device. The typical differentiation of the port as input/output no longer applies. In standard mode without IO-Link every port of an IO-Link capable device can still be configured as input or output.


The device can signal an incorrect operating status to the master per event. This is done by setting a bit in the interface. The master reads this event with a classifying error code.


Field Device Tool (e.g. ifm Container)

GSD file

Device master file - describes an interface to the device which is to be connected to the fieldbus. GSD files are available as files and provided by the device manufacturer.


Operating and observation device of the automation system (Human Machine Interface).


In contrast to the gateways hubs establish connections between two identical interfaces; known are USB hubs.

Hybrid device

A device combining both sensor and actuator functions.

IEC 61131

The international standard IEC 61131 deals with the basics of programmable logic controllers. Part 9 describes IO-Link under the designation single-drop digital communication interface for small sensors and actuators (SDCI).


Electronic device description (IO device description).

IO-Link device

Field device that is monitored and controlled by an IO-Link master.

IO-Link master

Establishes the connection between a higher-level fieldbus and the IO-Link device. The IO-Link master monitors and controls the IO-Link devices.

MES (Manufacturing Execution System)

An MES is a level of a multi-layer process-oriented production management system. It distinguishes itself from similarly efficient systems for production planning, i.e. ERP systems (Enterprise Resource Planning) by direct connection to the distributed systems of process automation. The MES allows production processes to be managed and controlled in real time. This includes conventional data acquisition and data preparation such as production data acquisition (PDA), machine data acquisition (MDA) and personnel data acquisition, as well as all other processes immediately influencing the production process.


An IO-Link communication channel.

Parameter setting server

An IO-Link master to IO-Link specification 1.1 can act as parameter setting server for the IO-Link device.

Point-to-point connection

A point-to-point connection is a direct, immediate connection between two points, places or devices.


Device that detects and converts physical values into electrical quantities.


Standard Input Output: This mode is used to operate conventional digital devices connected to IO-Link master ports and IO-Link sensors used without IO-Link structure.


A PLC is an industrial computer used to control a machine or system and programmed on a digital basis. The user programs a PLC according to the requirements of his system. The peripheral signals are read or provided via input/output modules or fieldbus masters and decentralised fieldbus slaves.


Bus participant that does not communicate independently but only replies to requests from the master.

Conversion time

The conversion time is the sum of the time the A/D converter needs to record the measured value and the time needed to process the measured value and the diagnostics and wire-break monitoring information in the module.

Cyclic data

Data that is transferred automatically and at regular intervals (process data, value status).

Cyle time

In the context of controllers, the cycle time means the processing of the program from reading of the inputs to the provision at the outputs. In the context of communication systems, the cycle time is the time until all data has been exchanged with all participants and the cycle starts again. For IO-Link, it varies depending on the transmission rate. With COM3, a complete transmission cycle takes 0.46 milliseconds. With COM2, the cycle time is 2.3 milliseconds.