ABB FSO-12, User Manual

Page: 32 / 388

32 Safety information and considerations
enough by coasting, the rotation must be stopped with external device, for example
with a safe brake.
It is not allowed to use the safe speed estimation with an external active load that can
accelerate the motor shaft. For example, in a hoist drive, the hanging load would
potentially cause an accelerating motion because of the gravity, thus the safe speed
estimate cannot be used for these types of applications.
WARNING! Applications with external active load must use a safety encoder
and FSO-21 and FSE-31 modules.
The diagram below shows an example of the SLS function, and the behavior of the
safe speed estimation with an induction motor and its slip. It also illustrates the
possible effect (unnecessary limit hit) if you do not take the slip into account when
defining the trip limits in the FSO module.
In the example, the motor torque is 100% during the acceleration and the motor slip is
at its maximum value. The FSO module speed estimates (ch1 & ch2) reach the SLS
trip limit even though the compensated value of the actual speed of the motor stays
below the SLS trip limit.
When acceleration is completed, the motor torque decreases. The FSO module
speed estimates show the actual motor speed and the slip is not any more visible in
the signal.
A SLS trip limits
Actual speed
Safe speed estimate
Slip
A
A
1
Motor speed
Time