Abbrev. Ref.
Description
Cat.
EN ISO
13849-1
Category, level “B, 1-4”
FIT
Failure In Time: 1E-9 hours
HFT
IEC 61508
Hardware Fault Tolerance: HFT = n
means, that n+1 faults could cause a
loss of the safety function
MTTFd
EN ISO
13849-1
Mean Time To Failure - dangerous. Unit:
years
PFH
IEC 61508
Probability of Dangerous Failures per
Hour. This value shall be considered if
the safety device is operated in high
demand (more often than once per
year) or continuous mode of operation,
where the frequency of demands for
operation made on a safety-related
system is greater than one per year
PFD
IEC 61508
Average probability of failure on
demand, value used for low demand
operation.
PL
EN ISO
13849-1
Discrete level used to specify the ability
of safety related parts of control
systems to perform a safety function
under foreseeable conditions. Levels a-e
SFF
IEC 61508
Safe Failure Fraction [%] ; Percentage
part of safe failures and dangerous
detected failures of a safety function or
a subsystem related to all failures.
SIL
IEC 61508
Safety Integrity Level
STO
EN
61800-5-2
Safe Torque Off
SS1
EN 61800
-5-2
Safe Stop 1
Table 2.2 Abbreviations Related to Functional Safety
2.6.1 Terminal 37 Safe Torque Off Function
The FC 102 is available with Safe Torque Off functionality
via control terminal 37. Safe Torque Off disables the
control voltage of the power semiconductors of the
frequency converter output stage which in turn prevents
generating the voltage required to rotate the motor. When
the Safe Torque Off (T37) is activated, the frequency
converter issues an alarm, trips the unit, and coasts the
motor to a stop. Manual restart is required. The Safe
Torque Off function can be used for stopping the
frequency converter in emergency stop situations. In the
normal operating mode when Safe Torque Off is not
required, use the frequency converter’s regular stop
function instead. When automatic restart is used – the
requirements according to ISO 12100-2 paragraph 5.3.2.5
must be fulfilled.
Liability Conditions
It is the user’s responsibility to ensure personnel installing
and operating the Safe Torque Off function:
•
Read and understand the safety regulations
concerning health and safety/accident prevention
•
Understand the generic and safety guidelines
given in this description and the extended
description in the
Design Guide
•
Have a good knowledge of the generic and safety
standards applicable to the specific application
Standards
Use of Safe Torque Off on terminal 37 requires that the
user satisfies all provisions for safety including relevant
laws, regulations and guidelines. The optional Safe Torque
Off function complies with the following standards.
IEC 60204-1: 2005 category 0 – uncontrolled stop
IEC 61508: 1998 SIL2
IEC 61800-5-2: 2007 – safe torque off (STO)
function
IEC 62061: 2005 SIL CL2
ISO 13849-1: 2006 Category 3 PL d
ISO 14118: 2000 (EN 1037) – prevention of
unexpected start-up
The information and instructions of the
Operating
Instructions
are not sufficient for a proper and safe use of
the Safe Torque Off functionality. The related information
and instructions of the relevant
Design Guide
must be
followed.
Protective Measures
•
Safety engineering systems may only be installed
and commissioned by qualified and skilled
personnel
•
The unit must be installed in an IP54 cabinet or
in an equivalent environment. In special
applications a higher IP degree may be necessary
•
The cable between terminal 37 and the external
safety device must be short circuit protected
according to ISO 13849-2 table D.4
•
If any external forces influence the motor axis
(e.g. suspended loads), additional measures (e.g.,
a safety holding brake) are required to eliminate
hazards
Introduction to VLT® HVAC D...
Design Guide
MG11BC02
Danfoss A/S © Rev. 06/2014 All rights reserved.
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