20
Festo — CMMT-ST-C8-1C-...-S0 — 2021-04b
Installation
Fig. 8: Connection example for cross-wiring several devices with checking of individual diagnostic
contacts
Connection example for mixed cross-wiring of devices with diagnostic contact (CMMT-ST) and
diagnostic output (e. g. CMMT-AS)
If errors are made when wiring the diagnostic contacts, they will cause incorrect diagnostic feedback
signals. With mixed wiring, special care is therefore needed. Only wire devices as described below.
Devices with diagnostic output must always be wired in parallel, e. g. all CMMT-AS. The signal must
then be connected to the diagnostic contact of the first CMMT-ST. The diagnostic contacts must then
be wired in series. The last CMMT-ST must then be connected to the safe controller for evaluation of
the diagnostic information.
This type of wiring is not permitted for operation with EC motors and the required safety classification
to SIL 3, cat. 3, Ple (
Fig. 8). Here, the diagnostic contacts of the CMMT-ST must be individually
evaluated.
The maximum number of 10 devices applies in this case for all devices wired together, regardless of
the type.
