Why IO-Link
Traditional sensors transmit only a single signal - on or off, or an analog value. IO-Link unlocks all the information the sensor's microprocessor already processes but that the standard binary connection cannot pass through: parameters, diagnostic data, status information.
Three things change as a result:
Data quality improves.
In an analog system, the signal passes through multiple analog-to-digital conversions on its way from sensor to PLC - each one loses precision. IO-Link performs a single conversion at the sensor and transmits a digital signal. 16-bit digital precision compared to 8–16-bit in analog systems.
Device replacement becomes simpler.
The IO-Link master stores each sensor's parameters. If a sensor fails, the replacement is connected in its place - the master automatically transfers all previous parameters to the new device. The operator does not need to know the sensor configuration and no special training is required. Unplanned downtime drops from hours to minutes.
Cable costs decrease.
Analog systems require shielded cables with specific connectors for signal transmission. IO-Link operates with standard 3-conductor, unshielded M12 cables - the same ones already used for conventional sensors. A single cable type for all sensors means simpler inventory and lower integration costs.
How IO-Link Fits into the Automation System
IO-Link is not a fieldbus protocol - it operates one level below, between the sensor and the master device. The IO-Link master then connects to any higher-level protocol: PROFINET, EtherNet/IP, Modbus TCP, PROFIBUS, DeviceNet, or CANopen.
Master devices
Available in two formats. Block I/O systems with 4 or 8 IO-Link ports (for example, the Turck TBEN-S2-4IOL) are designed for compact field-level installations at IP67 protection rating. Modular I/O systems allow a large number of IO-Link ports to be built up in a single remote I/O node.
I/O hubs
Allow standard 24 VDC digital devices (conventional sensors and actuators without IO-Link) to connect to an IO-Link master port through a single M12 cable. One I/O hub, such as the Turck TBIL-M1-16DIP, transmits 16 digital input signals over a single standard sensor cable. Instead of each sensor being wired individually to the control cabinet, 16 signals travel over one cable.
Advanced Functions
IO-Link's core function - digital transmission of process data - is useful on its own. But the protocol also offers additional capabilities that can be adopted gradually.
Parameter storage.
The master stores the configuration of each connected sensor. In case of replacement, parameters are automatically transferred to the new device.
Device verification.
IO-Link checks whether the replacement device is the correct product - by manufacturer, device type, or even serial number. This prevents errors when sensors are visually similar but have different specifications.
Advanced diagnostics.
Sensors can report not only process data but also their own condition - signal quality, temperature, operating hours. For example, a contactless encoder can warn if impact or vibration has shifted the positioning element - before a signal failure occurs. This is the foundation for predictive maintenance.
Acyclic parameter access.
IO-Link allows reading and writing sensor parameters from the PLC during operation, without stopping the system. This is useful when production requires changes to sensor threshold values or sensitivity settings.
Application Specific Tag.
Each IO-Link device can be assigned a text identifier. This simplifies device identification within a system - for example, when an inductive sensor on a workpiece carrier not only checks the part's position but also identifies the carrier itself.
When IO-Link Is and Isn't the Right Fit
IO-Link is a good choice when:
- I/O density is growing but PLC upgrade options are limited - IO-Link masters and hubs allow adding new I/O points without replacing the PLC
- Analog infrastructure is aging and maintenance costs are rising - IO-Link replaces analog signals with a universal digital interface
- Cable variety and integration complexity are driving up costs - a single M12 cable type for all sensors
- Device replacement requires a specialist and lengthy configuration - automatic parameter transfer resolves this
- Diagnostic information from sensors is unavailable - IO-Link makes it accessible without additional components
IO-Link may not be the best choice when:
- Speed is critical - IO-Link update time is 2.3 ms or slower, which is not fast enough for high-speed positioning or motion control applications
- Data volume is large - process data is limited to 32 bytes; in RFID applications with large data volumes this can be a constraint
- The existing system fully meets requirements and no expansion is planned
Start writing here...