IO-Link communication protocol: features, applications, and use guide
I’m sure you’ve heard of IO-Link over the last few years. IO-Link has its own standard, IEC 61131-9, and its community claims it as the first standardized input/output technology. This serial and bi-directional protocol has become popular because of its simple setup.
Many vendors already produce and design IO-Link devices to meet the new demand for this tech. Today, let’s learn a bit about its history, operation, and of course, its pros and cons.
What is IO-Link?
Developers created this protocol to simplify data exchange between field sensors from different brands. Then, IO-Link vendors gathered to build on this idea, creating the IO-Link community consortium. Today, the consortium has a large list of members, such as Advantech, Banner, Endress+Hauser, and Rockwell.
This point-to-point system establishes communication with sensors and actuators using a three-wire cable that needs no extras. This graphic depicts an example of its topology:
IO-Link also exchanges three types of data – process, service, and event data.
First off, as I already mentioned, the network uses only a three-wire cable that allows M5, M8, and M12 connectors. However, most devices use the M12.
The network has five elements to connect sensors and actuators to the controller.
First, you need the IO-Link master to connect the field devices with the automated control system. You can install it in the control system or as an IO system. Its inputs make point-to-point connections with the sensors, allowing digital and analog values of 8, 12, and 16 bits. On top of that, the master can use many types of Fieldbus or product-specific backplane buses.
Second and third, you need IO-Link sensors and devices, such as flow meters and valves. While you can use IO-Link devices in standard systems, you can’t do the reverse.
Fourth, you need the right cables to connect everything. For that, you can use unshielded three- or five-wire cables with M5, M8, or M12 connectors.
Last, you must have an engineering tool to set up the sensors and assign the parameters.
Simple and flexible connection
IO-Link can connect multiple smart devices in a single address, allowing a wide variety of devices in your network. This ability provides many benefits, like IO-Link blocks.
It also makes device replacement easy, because the protocol can set up a new device automatically from the controller. So it saves maintenance time and effort, always a big plus. IO-Link makes setting parameters easy too. This feature saves time and hassle during installation, another big plus.
Finally, IO-Link is an open solution that has an international consortium with many vendors as members. You get more options for your process if you don’t have to stick to one vendor.
How does IO-Link work?
The IO-Link master can have different operating modes for its ports. IO-Link mode sets the port for IO-Link communication. Then DI mode sets the port to behave as a digital input, and DQ mode as a digital output. Last, we have the deactivated mode. If you decide not to use a port, then you can configure it as deactivated.
The transmission rate, also known as baud rate, comes in three types for version V1.1:
- COM 1 = 4.8 Kbaud
- 2 = 38.4 Kbaud
- 3 = 230.4 Kbaud (optional based on V1.0 specification)
IO-Link sensors and actuators support only one baud rate each. But the master supports all of them and adapts automatically to the baud rate of each device based on the V1.1 specification.
And let’s not forget response time. This depends on many factors – the device description files, the device’s minimum cycle, the master’s internal processing time, and more.
Now let’s get into the types of data!
The process data contains the input and output from the sensors and actuators. This data updates every cycle, usually every two milliseconds, and sends between one and 32 bits.
You can retrieve information from the field device using service data units (SDUs). It communicates using up to 16000 blocks, and you can get all the basic device information – serial number, type, version, etc. You can get advanced information too, such as diagnostics and configuration.
Any event occurring in the network or with the devices, such as alarms, will trigger messages as soon as the devices recognize the event.
According to the consortium, you have four types of event data:
- Process data (cyclic)
- Value status (cyclic)
- Device data (acyclic)
- Events (acyclic)
Today’s technology demands easier, faster, and cheaper data collection. Wireless communication provides all of those benefits and has grown popular in process automation. Many users already feel familiar with the tech from using it in their daily lives.
Today, the discussion on wireless has changed from “how does it work?” to “how will it benefit my plant?” The consortium has stayed current by releasing the IO-Link wireless standard. It covers digitalization, beefing up the tech and offering a wide range of possibilities using IO-Link.
How does IO-Link Wireless work?
The network consists of a gateway, working as the network master, with devices connected to it. Of course, you’ll need an engineering tool to set up and assign parameters.
The network topology resembles the standard IO-Link, using the star layout to connect the devices with the master. If you have a wired device, then the network supports a bridge to send its data wirelessly to the gateway.
The wireless network uses three types of data. Yes, again. The process data exchanges up to 32 bytes every cycle. Then, the value status data confirms the validity of the process data. Last, the parameter and diagnostic data provide operating conditions, warnings, failures, and more.
This graphic shows wireless and wired IO-Link architecture:
Pros and cons of IO-Link
Now for the advantages and disadvantages of using this solution in your plant.
- Save time during device setup
- Save money on installation structure and network architecture
- High-level diagnostics from sensors and actuators
- Must have less than 20 meters between remote IO and IO-Link component
- Not recommended for high volumes of data or high-speed communication to the control