Festo — CMMT-ST-C8-1C-...-S0 — 2021-04b
Technical data
27
Safety reference data for the safety sub-function STO
Circuitry
Stepper motor
EC motor without
evaluation of STA
EC motor with eval-
uation of STA
Average diagnostic
coverage in accordance
with EN ISO 13849-1,
DC
AVG
[%]
90
87
92
Operating life (mission
time) in accordance
with EN ISO 13849-1,
T
M
[a]
20
Proof test interval
in accordance with
EN 61800-5-2, PTI
1)
[a]
20
2)
20
3)
20
4)
Classification of com-
ponents in accordance
with EN 61508
Type B
Hardware fault toler-
ance in accordance
with EN 61508, HFT
1
Common cause factor
for dangerous unde-
tected failures
β
in accordance with
EN 61508
[%]
2
1) Depending on the desired safety classification, the evaluation of the diagnostic contact STA by the safety relay unit is required or
optional.
2) To achieve the safety classification SIL 3 cat. 3, PL e with stepper motor, the evaluation of the diagnostic contact STA is optional. An
annual test interval is recommended.
3) To achieve the safety classification SIL 2 cat. 3, PL d with EC motor, the evaluation of the diagnostic contact STA is optional. An annual
test interval is recommended.
4) To achieve the safety classification SIL 3 cat. 3, PL e with EC motor, the evaluation of the diagnostic contact STA is required. This
requires a cyclical test that involves dynamically changing the input signals and then evaluating STA in accordance with EN 13849-1
at least once every 3 months in accordance with EN 61800-5-2.
Tab. 12: Safety reference data for the safety sub-function STO
The technical data for the safety sub-function SS1-t must be calculated individually according to the
application. Use the specified safety reference data for STO for the calculation.
