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ISD Safety Concept
8.3 Activating/Deactivating the Safe Stop
Function
The safe stop function is activated by removing the 24 V
DC voltage from pin 4 (safety) of the servo drive. This
causes the internal inverter to be blocked in accordance
with the requirements of Category 3. Safe stop can be
used to prevent an unexpected start. This means that the
24 V DC voltage must be re-applied to pin 4 of the servo
drive to end the safe stop and resume normal operation.
After this the drive must be restarted via the CAN bus.
NOTE
Servo drives with part numbers 175G7825 and 175G7826
are not suitable for the safe stop function.
WARNING
RISK ANALYSIS REQUIRED
8
8
Before installing and using the safe stop function, a
thorough risk analysis of the installation must be carried
out in order to ensure that the safe stop function and the
safety level achieved are sufficient and suitable. A commis-
sioning test must be performed after the safe stop
function is installed. Successful completion of an
acceptance test is obligatory for compliance with Category
3 PL under EN ISO 13849-1. The test is described in
8.5 Acceptance Test.
The following technical data applies to the various safety
levels:
•
Typical response time: 1.14 s
•
Maximum response time: 2.14 s The response
time is the elapsed time between removal of the
24 V DC voltage and switching off the gate driver
of the bridge inverter.
Data for EN ISO 13849-1
•
Performance level "d"
•
Mean time to dangerous failure (MTTFD): > 62
years
•
Diagnostic coverage (DC): 60%
•
Category 3
•
Lifetime 20 years
28
®
VLT
ISD 410 Servomotor Operating Instructions
Data for EN IEC 62061, EN IEC 61508, EN IEC 61800-5-2
•
•
•
•
Abbreviation Reference
Cat.
FIT
HFT
MTTFd
PFH
PL
SFF
SIL
STO
Table 8.1 Abbreviations
®
MG75D102 - VLT
is a registered Danfoss trademark
SIL 2 suitability, SILCL 2:
Probability of dangerous failure per hour (PFH):
-8
4.0625 x 10
/h
Safe Failure Fraction (SFF) >90%
Hardware fault tolerance (HFT):
1 [0] (1002 [1001D] architecture)
Description
EN ISO
Category 1-4
13849-1
–
Failure in Time; failure rate: 1E-9
hours
IEC 61508
Hardware Fault Tolerance; HFT = n
means that n + 1 faults may lead
to a loss of the safety function
EN ISO
Mean Time to dangerous Failure;
13849-1
Mean time to a dangerous failure:
(number of units)/(number of
undetected dangerous faults)
during the measuring interval
under the stated conditions
IEC 61508
Probability of dangerous failures
per hour: This value must be taken
into account when the safety
device is operated in high demand
mode (more than once per year)
or in continuous demand mode,
with the demand on the safety-
related system occurring more
than once per year.
EN ISO
Performance level; a discrete level
13849-1
used to specify the capability of
safety-related parts of a system to
perform safety-oriented functions
under given conditions. Levels: a-e
IEC 61508
Safe Failure Fraction [%];
proportion of safe failures and
detected dangerous failures of a
safety function or a subsystem as a
percentage of all possible failures
EN 61800-5-2 Safety Integrity Level
EN61800-5-2
Safe Torque Off
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