ABB FSO-21, Руководство пользователя

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Overview 45
Restrictions for the use of safe speed estimate
As the safe speed estimation is based on the drive electrical output frequency, there
are characteristics which must be taken into account:
1. Safe speed estimate is available when the drive is modulating. If the motor shaft
speed information must be safely available when the drive is not modulating, use
a safety encoder together with the FSO-21 and FSE-31 modules for measuring
the motor shaft speed.
2. Safe speed estimate can be used in applications without external active loads (for
example, hanging load).
3. If the motor has slip (for example, an induction motor), the safe speed estimate
differs from the drive actual motor shaft speed roughly the amount of the slip. See
the graph below which illustrates the effect of the slip.
4. When the motor operates near zero speed (below 2 Hz / 3% of the nominal
speed), there is ripple in the safe speed estimate signal. If the speed close to this
region needs to be monitored by the FSO module using the safe speed estimate,
the applicability of the estimate must be checked and considered case-by-case.
For example, the motor type and number of pole pairs.
5. The drive and motor shall be dimensioned considering the application (for
example, inertia, operating environment, etc). The dimensioning shall be such
that all functions can be performed without exceeding the specified operating
limits of the drive and motor.
6. The drive shall be dimensioned considering the motor and vice versa (for
example, nominal current, nominal power, etc).
7. In the event of motor control loss, the motor shaft mechanical speed and the drive
electrical output frequency can have a significant difference. The event can occur
due to:
•
incorrect dimensioning of motor or AC-drive compared to the load (for
example, inertia)
• AC-drive motor control firmware failure
• external active load
• generator mode.
If deceleration is safety-related in the application, use a safety encoder together with
the FSO-21 and FSE-31 modules for measuring the motor shaft speed, or use safety
functions with ramp monitoring.
Note: When the motor shaft speed is below the monitored speed limit, then the motor
shaft cannot accelerate over the speed limit, even in the event of motor shaft control
loss.
The safe speed estimate calculated by the FSO module does not include slip
compensation for the induction motors. You must take this into account when you