Recommendation: The safety relay unit should check the status of the diagnostic output at each STO
request. The level of STA must change according to the logictable. The safety relay unit can cyclically
test the signals #STO-A and #STO-B, for high level with low testimpulses and for low level with high
testimpulses.
Timing STO
Fig. 4 STO timing diagram
Legend for STO timing
Term/abbreviation
Explanation
#STO-A/#STO-B
2-channel input for STO request
#STO-HS/#STO-LS
Internal triggering, PWM driver high side/low side
t
STO,TP
Max. length, low test impulses
1)
at #STO-A/B
t
STO,In
Max. delay until STO switches off (≤ permissible reaction time when a safety
function is requested
1)
)
Product overview
10
Festo — CMMT-AS-...-S1 — 2018-02