3 SSI interface
The encoders provide an absolute signal of
a guided or free positioning element. The
sensor is contactlessly coupled with the po-
sitioning element via a stable inductive RLC
circuit.
In addition to the indication of process val-
ues via current and voltage outputs, the SSI
interface (Synchronous Serial Interface) has
become an established alternative in the
field of industrial automation. The process
value is transmitted either directly to the
higher-level controller (with SSI-card) or
to an appropriate fieldbus participant that
connects to all standard fieldbuses, such as
piconet®, BL67, BL20 or BLcompact.
The advantage of the SSI-interface is that
signals are directly and digitally transmitted
via the SSI telegram and are therefore more
precise and immune to interferences. Not
only process data is transmitted via SSI tel-
egram but also diagnostic bits.
Contactless encoders with SSI interface –
SSI interface Description
The fieldbus device is the master com-
manding a clock signal to which the sen-
sor responds synchronously via the SSI
telegram. The clock rate and the data
frame length are specified by the master.
Depending on the length of the connection
cable different clock rates are recommend-
ed (see section "Commissioning" on page
6). In order to adapt the clock rate to the
cable length, it is adjustable on the master
side. The data frame length and the process
value displayed as Gray or binary code must
be the same on the master and sensor side.
The encoder position can be captured in the
SSI synchronous as well as in asynchronous
mode. You can toggle between both modes
with a DIP switch (see section "Parametriza-
tion via teach function ", page 8). The asyn-
chronous mode is factory set. This makes
the SSI encoder compatible with virtually all
major SSI masters.