Festo CMTT-AS S1 Series, Description, Page: 10 / 46

– 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 through
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 diagnost-
ic 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 likewise 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.
Product overview
10 Festo — CMMT-AS-...-S1 — 2018-10a