What is the speed of IO-Link?

08 Apr.,2024

 

Communication protocol

IO-Link is a short distance, bi-directional, digital, point-to-point, wired (or wireless), industrial communications networking standard (IEC 61131-9) used for connecting digital sensors and actuators to either a type of industrial fieldbus or a type of industrial Ethernet.[1] Its objective is to provide a technological platform that enables the development and use of sensors and actuators that can produce and consume enriched sets of data that in turn can be used for economically optimizing industrial automated processes and operations. The technology standard is managed by the industry association Profibus and Profinet International.

System overview

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An IO-Link system consists of an IO-Link master and one or more IO-Link devices, i.e. Sensors or Actuators. The IO-Link master provides the interface to the higher-level controller (PLC) and controls the communication with the connected IO-Link devices.

An IO-Link master can have one or more IO-Link ports to which only one device can be connected at a time. This can also be a "hub" which, as a concentrator, enables the connection of classic switching sensors and actuators.

An IO-Link device can be an intelligent sensor, actuator, hub or, due to bidirectional communication, also a mechatronic component, e.g. a gripper or a power supply unit with IO-Link connection. Intelligent with regard to IO-Link means that a device has identification data e.g. a type designation and a serial number or parameter data (e.g. sensitivities, switching delays or characteristic curves) that can be read or written via the IO-Link protocol. This allows parameters to be changed by the PLC during operation, for example. Intelligent also means, however, that it can provide detailed diagnostic information. IO-Link and the data transmitted with it are often used for preventive maintenance and servicing, e.g. it is possible to set an optical sensor in such a way that it reports via IO-Link in good time if it threatens to become dirty. Cleaning no longer comes as a surprise and blocks production; it can now be put on a production break.

The parameters of the sensors and actuators are device- and technology-specific, which is why parameter information in the form of an IODD (IO Device Description) with the description language XML. The IO-Link community provides interfaces to an "IODD Finder",[2] which can be used by engineering or master tools to present the appropriate IODD for a device.

Connector

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Cabling is in the form of an unshielded, three or five conductor cables, not longer than twenty meters, and a standardized four or five pin connector. The master and device pin assignment is based on the specifications in IEC 60947-5-2.[3] For a master, two port classes are defined, port class A and port class B. Port class A uses M5, M8, or M12 connectors, with a maximum of four pins. Port class B uses only M12 connectors with 5 pins. M12 connectors are mechanically "A"-coded according to IEC 61076-2-101.[4] Female connectors are assigned to the master and male connectors to the device.

At the master pin 1 to pin 3 provides 24V DC power with max. 200 mA for an optional power supply of the IO-Link device. Pin 4 is used as a digital input (DI) or digital output (DO) according to the IEC 61131-2 specification to allow backward compatibility to proximity sensors according to IEC60947-5-2 or other sensors or electrical switches.

The IO-Link master sends a wake-up current pulse to get the IO-Link device from the serial input-output (SIO) state into the single-drop digital communication interface (SDCI) state. In the SDCI state the IO-Link master exchanges information frames with the IO-Link device.

In a port class A the pins 2 and 5 are not specified and are left to the manufacturer to define. In a port class B the pins 2 and 5 are configured as an additional power supply.[5][6]

Protocol

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The IO-Link communications protocol consists of communication ports, communication modes, data types, and transmission speeds. The ports are physically located on the master, and provide it a means for connecting with terminal devices and for bridging to a fieldbus or Ethernet. There are four communication modes that can be applied to a port connected to a terminal device: IO-Link, DI, DQ, and Deactivated. IO-Link mode configures the port for bi-directional communications, DI mode configures it as an input, DQ configures it as an output, and Deactivated just simply deactivates the port. There are four data types: process data, value status data, device data, and event data. The protocol can be configured to operate at transmission speeds of either 4.8 kilobaud, 38.4 kilobaud, or 230.4 kilobaud. The minimum transmission time at 230.4 kilobaud is 400 microseconds. An engineering tool is used for configuring the master to operate as the network bridge.[7]

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IO-Link Wireless[8] is an extension of IO-Link on the physical level. An IO-Link Wireless Master ("W-Master") behaves like a Master to the superordinate system. There are only virtual ports "down" to the IO-Link Wireless Devices ("W-Devices").

A transmission cycle consists of two phases. To transmit output data, the W master sends a Multicast-W frame (Downlink) with data for the W devices in assigned time slots. Then the W-Master goes on reception and collects in the Uplink Data from the W-Devices which transmit one after the other according to an agreed fixed scheme.

To secure the transmission Frequency Hopping and Channel-Blacklisting are used.

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IO-Link Safety[9] is an extension of IO-Link by providing an additional safety communication layer on the existing master and device layers, which thus become the "FS master" and "FS device". One also speaks of the Black Channel principle. The concept has been tested by TÜV SÜD.

IO-Link Safety has also extended the OSSD (Output Switching Signal Device) output switching elements commonly used for functional safety in a non-contact protective device like a light curtain to OSSDe. As with standard IO-Link, an FS-Device can be operated both in switching mode as OSSDe and via functionally safe IO-Link communication.

During implementation, the safety rules of IEC 61508 and/or ISO 13849 must be observed.

Literature

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  • Joachim R. Uffelmann, Peter Wienzek, Myriam Jahn: IO-Link. The DNA of Industry 4.0. Edition 1. Vulkan-Verlag GmbH, Essen 2018, ISBN 978-3-8356-7390-8.

References

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Io-Link Communication Io-Link Io-Link Sensors

FAQs

How is IO-Link positioned?

IO-Link is typically used in an automation environment below the I/O level for individual linking of field devices.

Where is IO-Link used?

IO -Link is used predominantly in an industrial environment in automated production for linking sensors and actuators.

What setting options do I have with IO-Link capable sensors and actuators?

This depends on the possibilities implemented by the manufacturer, but in general:

  • Local operation using teach-in, setting potentiometers, etc.
  • Event-driven program running using a connected controller
  • Operator-driven program running, e.g. using an HMI interface
  • Engineering system
  • Installation of a sensor in a pre-planned automation station with stored basic sensor settings

This also enables dynamic changing of parameter settings. Automated new settings are also possible.

Is it possible to upgrade existing systems in existing field bus structures?

As long as the system map of IO-Link has already been implemented for the bus system in question, an expansion of existing bus systems is possible.

Is it possible to manually adjust the sensor or actuator?

This is a matter of the implementation stage on the part of the component manufacturer. In principle, local parameter setting can be completely blocked or enabled.

How does IO-Link function?

IO-Link is based on the familiar 3-conductor connection for a digital switching signal, in which the switching signal is issued as a serial telegram. This means additional information can be exchanged in the form of a serial protocol between the I/O level and the field device.

Is IO-Link another field bus?

No, IO-Link describes a point-to-point connection between a peripheral interface and a field device.

How long can the connection between interface and field device be?

The maximum extension for each individual connection is 20 m.

How fast is the transmission of a signal over an IO-Link connection?

The typical signal transmission time for a value of 16-bit length is 2 ms.

Is it possible to send safety-relevant data, such as E-Stop commands, over IO-Link?

The IO-Link Community is presently working on a specification for IO-Link Safety.

Is it possible to use an intrinsically safe signal?

No, IO-Link is system-constrained to preclude an intrinsically safe signal.

How is power enabled on actuators?

The potential-free contact is implemented on Pins 2 and 5. Here you would use a 5-conductor standard cable.

What do I need to watch for when wiring?

Standardized 3-conductor cables or, in the control cabinet, individual leads are used. No shield is required.

What kinds of connectors are required on the sensor side?

All kinds of connectors used today. No special IO-Link cables or connectors are required. The recommended minimum gauge values must be observed. For 20m cable length the min. cross-section is 0.34mm≤. Since unshielded cables can be used, M8 and M12 standard connectors are suitable.

What data are sent over IO-Link?

Process data (e.g. analog values, switching states) are sent cyclically, configuration data (e.g. activation, deactivation of functions) as well as identification data (manufacturer ID) typically at startup, and parameters (sensitivity, switching threshold) or diagnostics are sent as needed.

What happens when an IO-Link proximity switch is defective and no equal replacement is available?

An IO-Link proximity switch (one switching output) can also be replaced by a corresponding standard proximity switch. Not available then are automatic identification, re-parameterizing and other communication functions. In this case only the switching signal is sent.

What non-IO-Link capable sensors can be connected to an IO-Link Master?

Standard PNP outputs or push-pull outputs.

Is mixed operation of IO-Link and conventional devices possible?

Both device types can be operated in a system, since each IO-Link component has by specification the conventional switching operation as well.

What is IO-Link with respect to AS-i?

  • A supplement system for intelligent wiring systems like AS-Interface
  • IO-Link is based on conventional point-to-point wiring
  • IO-Link is directly integrated in the sensor
  • IO-Link requires no special cables
  • IO-Link requires no sensor addressing
  • IO-Link has no station limitation

Is IO-Link a competitor of AS-i?

No, because

  • It is point-to-point wiring
  • It is a supplementary system on the lowest field level
  • If offers no bus-typical line or star topology

Why is IO-Link needed?

IO-Link is needed because:

  • It closes the communication gap in the lowest field level
  • It makes validation of machines and equipment possible down to the lowest sensor and actuator level
  • It minimizes the variety of existing interfaces (PNP, push-pull, 4-20mA, 0-10V, RS232, and RS422 become IO-Link)

What changes at installation and during use?

  • Nothing changes in terms of wiring - IO-Link uses the well known standard sensor cables M12, M8, M5
  • IO-Link replaces cumbersum transmission of analog signals over shielded cable
  • IO-Link replaces costly multipole parallel wiring by a simple 3 wire standard cable
  • IO-Link standardizes interfaces and cables with a single type
  • IO-Link provides transparency down to the field device level

Which type of sensors can be connected in the SIO-mode of IO.Link

  • Binary Sensors with PNP output can be connected
  • Sensors with NPN output cannot be connected

Is the system simpler than familiar communications structures?

  • Higher order communications structures are generally bus systems
  • IO-Link is a point-to-point connection

How do I incorporate the system into familiar bus systems?

A part of project planning of sensors and actuators, expansions are added to the engineering tools. The device-specific data are provided, depending on the engineering tool, using specific device descriptions and parameter setting interfaces (based on IODD description files or DTMs or proprietary tools.

What is the speed of IO-Link?

FAQs