General
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1 General
1.1 STO Safety Function
Safety function for safety drives
● STO
The Safe Torque Off (STO) function immediately blocks the motor torque or power
output in electronic mode according to input signals from external devices. This
function complies with stop category 0 in EN
60204‑1. If the motor is still rotating
when the STO function is enabled, the motor will coast to a standstill.
1.2 Terms and Abbreviations
Term/Abbr.
Description
Cat.
Category of safety components in the control system. The categories
are B, 1, 2, 3, and 4.
DCavg
Average diagnostic coverage (%)
DTI
Diagnostic test interval
SFF
Safe failure fraction
PFHd
Probability of dangerous failure on demand per hour
PL
Performance level
SC
System capability
SIL
Safety integrity level
T
1
Proof test interval
DI
Digital input
DO
Digital output
MTTFd
Mean time to dangerous failure
1.3 Safety Standards
Standards compliance
● North American standards (UL)
UL
61800‑5‑1
CSA C22.2 No. 274
● EC directives and standards
Low Voltage Directive 2014/35/EU Standard EN
61800‑5‑1
EMC Directive 2014/30/EU Standard EN 61800‑3
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