V01.00 | 2021/05
9
4.3
Functional principle
The read/write heads are used for contactless data exchange with tags. For this the controller
sends commands and data via the interface to the read/write head and receives the corres-
ponding response data from the read/write head. The reading of the UIDs of all RFID tags in the
read area or the writing of an RFID tag with a specific production date are examples of typical
commands. To communicate with the tag, the data of the read/write head is coded and trans-
ferred via an electromagnetic field, which at the same time supplies the tags with power.
A read/write head contains a transmitter and a receiver, an interface to the interface module
and a coupling element (coil antenna) for communicating with the tag. Inductive coupling is
used for the transmission between read/write head and tag on devices for the HF range.
IC
Read/write head
HF: alternating electromagnetic field
Data carrier
Fig. 4: Operating principle of HF-RFID
The coupling element of the read/write head generates an electromagnetic AC field. This pro-
duces a transmission window as a so-called air interface in which the data exchange with the
tag takes place. The size of the transmission window depends on the combination of read/write
heads and tags.
Each Turck read/write head can communicate with a number of Turck tags. This requires the
read/write head and the tag to operate in the same frequency range. Depending on the power
and frequency used, the device ranges vary from a few millimeters up to several meters. The
specified maximum read/write distances only represent typical values under laboratory condi-
tions without allowing for the effect of materials. The achievable distances may vary due to
component tolerances, the mounting situation in the application, ambient conditions and the
effect of materials (particularly metal and liquids).
4.4
Functions and operating modes
The devices enable passive HF tags to be read or written in single and multitag operation. For
this the devices form a transmission zone that varies in size and range according to the tags
used and the operating conditions of the application. Refer to the data sheets for the applicable
maximum read/write distances.
The devices can be operated in IO-Link mode or in standard I/O mode (SIO mode). IO-Link
mode provides bidirectional IO-Link communication between an IO-Link master and the read/
write heads. For this the devices are integrated in the controller level via an IO-Link master. The
data to be read or written is made available with the process data via the IO-Link interface. Be-
sides the read data, diagnostics and identification messages can also be queried via IO-Link.
Different device functions can be configured via the IO-Link interface.
SIO mode makes it possible to query the presence of tags or compare the data of two tags.
