The next step in the evolution of smart sensors is the new international standard called IO-Link. Developed by a consortium of leading sensor, actuator, and control technology suppliers, IO‑Link uses the same fieldbus connection that previously only monitored sensor output as a two-way communication system for complete sensor or actuator setup, calibration, and troubleshooting, in addition to process output.
An IO-Link system consists of an IO-Link master, a standard three-wire sensor/actuator cable, and an IO-Link enabled sensor or actuator. The master connects to the industrial field bus that already exists within the plant, or it could plug in as a module for a programmable-logic controller or other automation controller. The masters are designed to supplement the existing network, not replace it.
Each master can have one or more IO-Link device ports that connect on a one-to-one basis with an IO-Link-capable sensor or actuator. What makes the IO-Link ports unique is that they use the same three-wire connection used by most sensors: two-wires for power and ground, while the third is the output of the sensor or input to an actuator. The IO-Link master establishes a serial communication connection through the “output” wire to IO-Link-capable sensors.
When a sensor is plugged into an IO-Link master port, the port tries to establish communication with the device by sending it a special “Wake-up” sequence. Upon receiving this code, the device replies that it is awake. Once communication is established, the master sends and receives data through the link from the sensor. Not only can process data be sent from the sensor, but setup and calibration information can be passed back and forth as well as operation and error codes for troubleshooting.
Interestingly, if the master can’t establish a communication link, it reverts the IO-Link port to a standard sensor-bus interface port. This lets non-IO-Link sensors use the port just like any other fieldbus device port.
Hasn’t this been done before, you ask? Yes, but earlier smart device networks were proprietary. You couldn’t mix-and-match different manufacturer devices on the same network. IO-Link lets different manufacturers share the same field-bus connection.
Pepperl+Fuchs (www.am.pepperl-fuchs.com) supplied information for this column.
Edited by Robert Repas