The Drive Safety Function Failure Rate - Delta VFD300C43S-HS User Manual

Chapter 17 Safe Torque Off Function C2000-HS

17-1 The Drive Safety Function Failure Rate

Item
SFF Safe Failure Fraction
HFT (Type A
Hardware Fault Tolerance
subsystem)
SIL Safety Integrity Level
Average frequency of dangerous failure
PFH
[h-1]
Probability of Dangerous Failure on
PFD
av
Demand
Category Category
PL Performance level
MTTF Mean time to dangerous failure
d
DC Diagnostic coverage
17-2 Safe Torque Off Terminal Function Description
The Safe Torque Off function (STO) is to cut off the power supply to motor through the hardware,
thereby the motor could not produce torque.
The STO function controls the motor current driving signal through two hardware circuits respectively,
and thus cut off the inverter power module output in order to achieve the status of safety stop.
Operation principle Description as following table 1:
Table 1: Terminal operation description
Signal Channel
STO1–SCM1
STO signal
STO2–SCM2
Driver Output status
 STO means Safe Torque Off
 STL1–STL3 means Safe Torque Off hardware abnormal.
 STL3 means STO1–SCM1 and STO2–SCM2 internal circuit detected abnormal.
 STO1–SCM1 ON (High): means STO1–SCM1has connection to a +24V
 STO2–SCM2 ON (High): means STO2–SCM2 has connection to a +24V
 STO1–SCM1 OFF (Low): means STO1–SCM1hasn't connection to a +24V
 STO2–SCM2 OFF (Low): means STO2–SCM2hasn't connection to a +24V
Definition
Photo-coupler status
ON (High) ON (High)
ON (High) OFF (Low)
STL2 mode
Ready (Torque output
off)
17-2
(Applying Certifications)
Standard
Channel 1: 80.08%
IEC61508
Channel 2: 68.91%
IEC61508 1
IEC61508 SIL 2
IEC62061 SILCL 2
IEC61508 9.56×10
IEC61508 4.18×10
ISO13849-1 Category 3
ISO13849-1 d
ISO13849-1 High
ISO13849-1 Low
OFF (Low)
ON (Low)
STL1 mode
(Torque output
off)
DC
Performance
-10
-6
OFF (Low)
OFF (Low)
STO mode
(Torque output
off)
power supply.
power supply.
DC
power supply.
DC
power supply.
DC