In this video, we’re going to learn about IO-Link.
What is IO-Link I hear you say?
Well, listen closely, and you’ll find out!
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IO-Link is a communications protocol that works point-to-point.
A point-to-point communication connection
is a communications connection between two separate endpoints or nodes.
IO-Link is bi-directional meaning it works two ways,
and works over a short distance.
It is primarily used to communicate with sensors and actuators
in plant or factory automation processes.
Sensors and actuators are usually connected via Fieldbus connections,
allowing them to be in remote locations.
With IO-Link, the field devices,
such as actuators or sensors,
connect to a ‘Master’ device which communicates to a controller,
usually a PLC, or Programmable Logic Controller.
The connection between the IO-Link Master and the field device
is established via an unscreened 3 wire cable,
no more than 20 meters long.
The IO-Link master is capable of processing digital signals and analog values.
Its versatility means it is capable of integrating into existing systems
and can communicate using the industry-recognized Profinet,
Profibus, or Modbus, to name a few.
The IO-Link master establishes the connection between the IO-Link devices
and the automation system.
As a component of an I/O system,
the IO-Link master is installed either in the control cabinet
or as remote I/O, directly in the field.
An IO-Link master can have several IO-Link ports or channels.
An IO-Link device can be connected to each port,
meaning IO-Link is a point to point communication and not a Fieldbus.
The IO-Link protocol allows an IO-Link port
to be operated in one of four different operating modes.
The first mode is the IO-Link mode.
This means that the port is used for IO-Link communication.
The second mode is the DI mode.
This means that the port acts in the same way as a digital input device.
The third mode is the DQ mode.
This means that the port acts in the same way as a digital output device.
The fourth mode is Deactivated.
This means that the port is not assigned to any other modes
and is reserved for when the port is unused.
IO-Link is a very robust communication system That operates using 24 volts.
Transmission errors can occur for a number of reasons,
in general a cable fault or a power surge can temporarily interfere with transmissions.
If an error is detected,
the message attempts transmission up to an additional two times.
Only after the transmission has failed for a third time
does the IO-Link master recognize a communication failure.
Upon recognizing this,
the IO-Link master will signal the communications failure
to the higher-level controller.
This can then alert operators or maintenance staff of the issue,
so they can physically attend to and rectify the problem.
An IO-Link device has 4 types of transmission.
“Process Data”, “Value Status”, “Device Data”, and “Events”.
The Process Data is considered as the latest state of the sensor or actuator,
such as speed.
Process Data is transmitted cyclically,
which means automatically, at regular defined intervals.
Up to 32 bytes of process data can be processed,
and it’s defined by the high-level controller.
The Value Status indicates whether the Process Data is valid or invalid
and is transmitted along with the Process Data cyclically.
The Device Data holds detailed information about a device.
Basic information such as the serial number or version number
and more advanced information
such as parameters or diagnostic information
are able to be retrieved from each IO-Link device.
Device Data is transmitted acyclically,
at the request of the IO-Link master.
This means that it is not automatically transmitted
but will be transmitted after a request from the IO-Link Master.
Device Data can be read from the device, but also written to.
A device is able to trigger an Event,
which in turn signals the presence of an Event to the IO-Link Master.
An example of an event is an error or warning message,
for example a short circuit, or a device that is overheating.
This information can be used to display indicators or messages on HMI devices,
such as error messages signalling a wire break
or a communication failure,
once the IO-Link Master has processed the message to the High-Level controller.
The transmission of device parameters and events
occurs independently from the cyclic transmission of Process Data.
This means that they do not impact each other,
so critical messages do not have to queue,
until already buffered messages are sent.
So, let's try and summarise what we’ve learned today.
IO-Link is a simple communications protocol.
It is used primarily for communications to simple 3 wire sensors and actuators.
An IO-Link Master has slave devices,
such as an actuator or sensor, attached to it.
The IO-Link Master can then communicate over a Fieldbus connection
to the higher-level controller,
most likely in our case, a PLC, or Programmable Logic Controller.
The IO-Link ports can serve different purposes,
from signaling that it is unused,
to signal that it is in Input mode,
Output mode or for IO-Link communication.
An IO-Link device transmits Process Data
and Value Status periodically,
at a regular defined interval.
This is called cyclic transmission.
Device Data, such as diagnostics and Events
are transmitted when they are needed.
This is called acyclic transmission.
That’s it for this video! I hope you have enjoyed learning about IO-Link.
It is a very simple communications protocol
that can be quite complex to learn about!
Getting the set up of the IO-Link configuration correct
is heavily dependant on the device that is being communicated with,
so checking the field devices instructions
is a necessity to be able to communicate correctly.
Don’t worry though, once it is set up,
they are very easy to maintain,
and often work seamlessly with no additional work required.
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