Festo CMTT-AS S1 Series, Description, Page: 20 / 46

SBC request
If there are suspended loads, they usually drop if STO and SBC are requested directly before the brak-
ing ramp is completed because the engagement time of the holding brakes plays a significant role.
For details of how to wire up safety sub-function STO with SBC, see
è Fig.14.
• When selecting the delay time t
Delay
, make sure it is long enough to take account of the maximum
braking ramp time and brake engagement time.
4.1.5 Cross wiring of several servo drives
For cross wiring, wire the diagnostic outputs as a ring. Route both ends of the ring to a 2-channel input
of the safety relay unit. The safety relay unit monitors for discrepancies. A maximum of 10 servo drives
can be wired in parallel.
Cross-wiring, example STA
Fig. 11 Cross-wiring, example STA
For cross-wired diagnostic outputs, the condensed state results from a logical AND link. An output of a
CMMT-AS is capable of pulling all other outputs to low signal. A high signal is present at the two
inputs of the safety relay unit only if all diagnostic outputs deliver high signals. The ring-shaped cross
wiring of the diagnostic outputs with sensing at the beginning and end of the signal chain makes it
possible to detect cable breaks in the cross wiring.
At this point, the diagnostic outputs deviate from the closed current principle. Cyclical automatic test-
ing of the diagnostic output by the safety relay unit is therefore highly recommended
è STO feedback via STA diagnostic contact and è SBC feedback via SBA diagnostic contact.
4.1.6 Error exclusion
Put suitable measures in place to prevent wiring errors:
Product overview
20 Festo — CMMT-AS-...-S1 — 2018-10a