Functions
8.18 Fail-safe functions
Control Units CU240S
Operating Instructions, 11/2006, A5E00766042B AA
8-115
Note
The fail-safe function SLS should not be activated during following processes are active:
• Search process in flying restart
• Motor data identification
• Speed control optimisation
It is recommended not to use the torque contol (P1300 = 22, 23 or P1501 > 0) as a control
mode for the fail-safe function SLS.
Caution
Reaction time
The reaction time for a SLS is 20 ms.
Fault reaction time
An internal failure during a SLS, which leads to an LSTO, will be detected within the time
specified in "Fault reaction time" of section "Limiting values for SS1 and SLS".
The overall reaction time is the sum of reaction time and fault reaction time.
Modes of behavior
The SLS function has three modes of behavior giving the user a choice of functionality to suit
their specific application. These modes of behavior of the SLS function are controlled by
setting the required values in parameters P9692 and P9892.
Caution
Due to monitoring reasons, the so called "accuracy limit for SLS" with a value of 1 Hz is set.
If - in SLS mode - the actual frequency under-runs this value, an STO is triggered.
Warning
If due to dynamic loads the frequency runs above the SLS limit (P9691/P9891) an LSTO is
triggered; if it falls below the accuracy limit an STO is triggered. Therefore when designing
the plant, dynamic load changes must be taken into account to prevent unintented activation
of fail-safe functions.
Furthermore the acceptance test should be performed under worst-case load conditions.
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