10
Festo — CMMT-AS-...-S1 — 2021-04d
Product overview
The drive behaves as follows when the safety sub-function STO is requested:
–
Behaviour of the drive with a running motor: the movement of the drive is not decelerated via a
braking ramp. The drive continues to move uncontrolled due to inertia or external forces until it
comes to a standstill by itself.
–
Behaviour of the drive with a stopped motor: the drive is uncontrolled and can be moved by external
forces.
STO feedback via STA diagnostic contact
The status of the safety sub-function STO can be reported to the safety relay unit via the STA
diagnostic output.
The STA diagnostic output indicates whether the safe status has been reached for the safety sub-func-
tion STO. The STA diagnostic output switches to high level only when STO is active on 2 channels via
the control inputs #STO-A and #STO-B.
#STO-A
#STO-B
STA
Low level
Low level
High level
Low level
High level
Low level
High level
Low level
Low level
High level
High level
Low level
Tab. 2: Level of STA
If protective functions are triggered on both channels (STO-A and STO-B), e.g. if the voltage at STO-A
and STO-B is too high, the internal protective functions switch off and STA also delivers a high level
signal.
Recommendation: the safety relay unit should check the status of the diagnostic output whenever
there is a STO request. The level of STA must change according to the logic table. The safety relay unit
can cyclically test the signals #STO-A and #STO-B for high level with low test pulses and for low level
with high test pulses.
