Smart Sensor Profile is the standardized device profile for measuring sensors and contains the standard functions of IO-Link devices. This ensures a uniform look and functionality regardless of the connected item’s manufacturer.
The IO-Link specifications are constantly being further developed. Version 1.1. was introduced as an improvement from the original version. It included data storage, mandated data transmission rate, and enables process data per port up to 32 bytes.
Ports are IO-Link communication channels between device and master. Generally, there are two port types in the specification for IO-Link masters: Port Class A (type A), Port Class B (type B). The IO-Link devices are connected to the master via unshielded 3-, 4- or 5-wire standard cables up to 20 m long. IO-Link requires only 3 wires each. The supply voltage is present at pins 1 and 3 (24 V max. 200 mA), pin 4 is the communication output.
IO-Link devices only support a data transfer rate specified in the IO-Link specification. The following data transfer rates are specified for IO-Link V1.1: COM1 = 4.8 kBaud, COM2 =38.4 kBaud, COM3 =230.4 kBaud
The cycle time provides information about the time intervals at which the Master can address the Device. Sensor technology (physical principle) has a great influence on the cycle time. The minimum cycle time is stored in the IODD. Devices with different minimum cycle times can be configured on one master.
The process data is transmitted cyclically in the form of a data telegram. The process data size is determined by the device.
Each port of the IO-Link master can be operated either in SIO mode (standard in-out mode: according to the latest specification DI mode for sensors and DQ mode for actuators) or in IO-Link mode and thus process the information of all sensors. In SIO mode, the binary switching output (NPN, PNP or push-pull) of the sensor is used. In IO-Link mode, the output of the sensor (pin 4) is used as a bidirectional, digital interface to exchange measurement and diagnostic information.
A Dual Channel transmits additional input and output signals in parallel to the IO-Link channel. Sensor operation provides maximum flexibility utilizing one channel or both simultaneously. This is also enabled if the sensor features several dual channels.
Depending on the control concept, dual channels can serve different purposes. In applications with very high real-time requirements, it can be useful to connect the dual channel directly to an actuator in order to eliminate delay caused by the controller’s cycle time. This allows to use IO-Link communication simultaneously e.g. to trigger an automatic format alignment or to evaluate secondary data.
If process control is primarily by analog dual channel, the IO-Link interface can support parameterization during setup or monitoring of downtime. In addition, it can be changed to work with digital controllers at all times.
Transmission and conversion of analog data is replaced by direct transmission of digital data to the controller, which guarantees high and loss-free data quality. IO-Link is a very robust communication system.
This communication system operates with a 24 V level. If transmissions fail, the telegram will still be repeated twice. Only after the second repeat attempt has failed does the IO-Link Master detect a communication interruption and report this to the higher-level controller.
Each IO-Link Device has a device description file, the so-called IODD (IO Device Description). This contains data about the manufacturer, article number, functionality, software version etc., which can be easily read out and further processed by the automation system. Each device, i.e. each sensor, can be uniquely identified both via the IODD and via an internal device ID. The identification data of the sensor also includes device or application descriptions that can be freely assigned by the user. The IODD consists of several files: a main file and optional external language files (both in XML format), as well as image files (in PNG format).
Sensors with IO-Link 1.1 can be operated as “Adjustable Switching Sensor (AdSS)” or “Digital Measuring Sensor (DMS)” according to the Smart Sensor Profile. When treated as AdSS or DMS the Sensors-Master communications happens via a fully standardized command set. Thus, operation without IODD file is possible. This can reduce integration cost tremendously. Please consult the datasheet, to find out if a specific sensor has AdSS or DMS.
Off-line sensor parameter adjustment via convenient user interfaces in the PC (via USB Master) or via Wireless App (via Wireless Master). Sensors can be conveniently configured at the desk and installed without further teach-in.
Even if IO-Link is not implemented in the machine control, sensors can be operated in SIO mode and use this advantage.
Programmable logic controllers (PLC) are programmed using so-called engineering tools (PC software). IO-Link sensors can be integrated directly into engineering tools. Parameter adjustment of the integrated sensor is also possible via the engineering tool.
If a sensor already integrated in an automation system has to be replaced (defect), an unconfigured replacement sensor can simply be integrated in the system and is automatically assigned the parameter data of the defective sensor by the master (parameter server of the master). Parameter data is stored both in the sensor and in the master (data storage).
Machines must be re-parameterized more frequently during operation in order to produce new recipes or formats. Sensors with IO-Link can automatically accept parameter sets stored in the control program for individual formats. This enables minimal changeover times.
Signalling e.g. by flashing LEDs on the sensor to locate and physically identify a sensor in a machine or system. The signalling can be triggered, for example, from the engineering tool of the controller.
To solve applications reliably and efficiently, sensors can be taught-in to the respective process conditions. The range of teach options on the sensor is limited but IO-Link opens up deeper options. In addition to the classic teach options, greatly enhanced settings such as filter functions, switching hysteresis, switching window or temperature compensation are also available via IO-Link. User interfaces on PC or mobile devices make them user-friendly. A programmable access lock (qTeach Lock) also prevents manipulation directly at the sensor.
Unlike conventional sensors, several process data (e.g. switching signal + distance + frequency) can be output simultaneously via the same channel via IO-Link. Process data are cyclic data which are transmitted regularly and quickly (maximum realizable speed corresponds to the cycle time of the automation system). These are used for process control in the automation system. Via the IO-Link master and protocols such as OPC UA or JSON, they can not only be transferred to the controller, but also to other IT systems (cloud).
Baumer sensors with IO-Link can realize and output additional evaluations in the sensor beyond the standard. These analysis functions do not have to be programmed separately in the controller and are acyclically available for evaluation if required. Examples are: Number of switching cycles, operating time, boot cycles, histograms of process data, as well as the operating voltage or device temperature. This additional data is also called diagnostic data and can be used, for example, to implement predictive maintenance.