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130BC318.10
time
1
2
A
A
Actual frequency
1
Activation of Safe Torque Off
2
Motor standstill
Illustration 3.2 Safe Torque Off
3.1.2 Specification of Safety Functions
The safety function specification contains details about
each safety function that should be executed, for instance:
•
Required interfaces with other control functions.
•
Required error responses.
•
Performance level required (PLr) or safety
integrity level (SIL).
3.1.3 Activation of Safety Functions
The safety functions are activated using the dual-channel
safe inputs on the safety option or using the PROFIsafe
communication.
These inputs operate in accordance with the idle current
principle (activate when switching off). The safety control
system activates the safety functions via a 1/0 transition.
3.1.4 Activation of STO from Multiple
Sources
If multiple sources activate STO (via digital inputs and safe
fieldbus), all sources must deactivate STO in the safety
option to return to normal operation. After all sources
deactivate STO, a reset of the safety option might be
required depending on the settings of the digital inputs.
3.1.5 Functional Proof Tests
The functional safety standards require that functional
proof tests are performed on the equipment used in the
system. Proof tests are performed at user-defined intervals,
and are dependent on PFD and PFH values.
3.1.6 PFD and PFH Definitions
Safety-related systems can be classified as operating in
either a low demand mode, or in a high demand/
continuous mode.
Low demand mode
The frequency of operation made on a safety-related
system is not higher than once per year. The SIL value for
a low demand safety-related system is directly related to
order-of-magnitude ranges of its average probability of
failure on demand (PFD).
High demand/continuous mode
The frequency of operation made on a safety-related
system is higher than once per year. The SIL value for a
high demand/continuous mode safety-related system is
directly related to the probability of a dangerous failure
per hour (PFH).
3.1.7 Internal Errors
Any internal error in the safety option activates the safety
function STO. The frequency converter coasts the motor.
Internal errors always require a power cycle of the
frequency converter to reset the error. Alternatively, use
42-90 Restart Safe Option
to restart the safety option after
internal error without power cycling the frequency
converter.
Functions
Safety Option MCB 152
10
Danfoss A/S © 10/2014 All rights reserved.
MG37F102
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3
Summary of Contents for MCB 152
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