2 Engineering
2.8 Safe Torque Off (STO)
50 Rapid Link 5 · RAMO5 · RASP5 05/20 MN034004EN www.eaton.com
2.8 Safe Torque Off (STO)
2.8.1 Overview
The function STO (STO = Safe Torque Off) is optionally available for the
RASP5 speed controller.
This function meets the requirements for variable-speed drive systems defi-
ned in Part 5-2 of the IEC 61800 standard and ensures that torque-generating
energy is no longer able to act on the motor shaft. Moreover, this state is
monitored internally in the drive.
The STO function can be used anywhere where the corresponding motor will
come to a zero speed by itself in a sufficiently short amount of time as a
result of the corresponding load torque or friction, as well as in cases in
which uncontrolled run-down (coasting to a stop) has no safety implications.
v = Motor speed
t1 = STO shutdown
Start of the uncontrolled run-down
Gray = run-down range of the drive
not relevant to safety
Figure 19: : STO conforming to Stop Category 0
￫
This safety function corresponds to uncontrolled stopping as
defined in IEC 60204-1, Stop category 0.
Additional measures (such as mechanical brakes) may be
required in order to prevent hazards in which external factors
are involved (e.g., suspended loads falling down).
￫
Application examples can be found in the Eaton safety manual
PU05907001Z.
You can find the safety manual as a PDF document on the
Eaton website at the following address:
http://www.eaton.eu/DE/Europe/Electrical/CustomerSupport/Techni-
calLiterature/SafetyManual/index.htm
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