General
‑12‑
1 General
1.1 Terms and Abbreviations
Terms and
Abbreviations
Description
Cat.
Safety category It includes B, 1, 2, 3, and 4.
CCF
Common cause failure
DCavg
Average diagnostic coverage (%)
DTI
Diagnostic test interval time
SFF
Safe failure fraction
HFT
Hardware fault tolerance
PFH
D
Probability of a dangerous Failure per Hour
PL
Performance Level
SC
Systematic capability
SIL
Safety integrity level
T
1
Test interval
DI
Digital input
DO
Digital output
PCB
Printed circuit board
MCU
Micro computer unit
FPGA
Field programmable gate array
MTTFd
Mean time to dangerous failure
STO
The safe torque off (STO) function brings the machine safely into a no‑
torque state and prevents it from unexpected start. If the motor is
running when STO function is activated, it coasts to 0 RPM.
Safe state
Disabling the PWM gating signal of the drive
System reset
Resetting the servo system through resetting the power supply or
executing software reset
Proof test
Tests used to detect the failure of safety‑related systems
Mission time
Specified cumulative operating time of the safety‑related parts of the
servo drive during its overall lifetime
1.2 Safety standards
Standards compliance
● North American standards (UL)
UL 61800‑5‑1
CSA C22.2 No. 274
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