6.5 STO Technical Data
The Failure Modes, Effects, and Diagnostic Analysis (FMEDA) is performed based on the following assumptions:
•
FC 280 takes 10% of the total failure budget for an SIL2 safety loop.
•
Failure rates are based on the Siemens SN29500 database.
•
Failure rates are constant; wear-out mechanisms are not included.
•
For each channel, the safety-related components are considered to be of type A with a hardware fault tolerance
of 0.
•
The stress levels are average for an industrial environment and the working temperature of components is up
to 85
°
C.
•
A safe error (for example output in safe state) is repaired within 8 hours.
•
No torque output is the safe state.
Safety standards
Safety of Machinery
ISO 13849-1, IEC 62061
Functional Safety
IEC 61508
Safety function
Safe Torque Off
IEC 61800-5-2
Safety performance
ISO 13849-1
Category
Cat. 3
Diagnostic Coverage (DC)
60% (Low)
Mean Time to Dangerous Failure
(MTTFd)
2400 years (High)
Performance Level
PL d
IEC 61508/IEC 61800-5-2/IEC 62061
Safety Integrity Level
SIL2
Probability of Dangerous Failure per
Hour (PFH) (High Demand Mode)
7.54E-9 (1/h)
Probability of Dangerous Failure on
Demand (PFD
avg
for PTI = 20 years)
(Low Demand Mode)
6.05E-4
Safe Failure Fraction (SFF)
> 84%
Hardware Fault Tolerance (HFT)
1 (Type A, 1oo2D)
Proof Test Interval
2)
20 Years
Common Cause Failure (CCF)
β = 5%; β
D
= 5%
Diagnostic Test Interval (DTI)
160 ms
Systematic Capability
SC 2
Reaction time
1)
Input to output response time
Enclosure sizes K1–K3: Maximum 50 ms
Enclosure sizes K4 and K5: Maximum 30 ms
Table 6.3 Technical Data for STO
1) Reaction time is the amount of time from an input signal condition that triggers the STO until the torque is off on the motor.
2) The way to perform proof test please refer to chapter 6.4 Maintenance and Service for STO.
Safe Torque Off (STO)
Operating Instructions
MG07A102
Danfoss A/S © 11/2015 All rights reserved.
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