ABB FSO-12, Руководство пользователя

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Safety information and considerations 31
Safe speed estimate
With safe speed estimate, the FSO module uses the drive output frequency
measurement to estimate the motor speed.
The FSO module has two safe speed estimation data channels. Speed in channel
one is received from the drive (
200.01 FSO speed ch1 ), and speed in channel two is
calculated by FSO module ( 200.02 FSO speed ch2 ). FSO compares these two speed
data sources. If the values differ too much, the FSO module detects it and goes into
the Fail-safe mode.
The nominal speed and nominal frequency of the motor must be set according to the
motor type designation label for the FSO module. See section
How to configure
general settings on page 224 .
It must be considered in the risk assessment of the application whether the safe
speed estimate can be used. See the restrictions below.
Restriction for the use of safe speed estimate
As the safe speed estimation is calculated based on the drive output frequency, there
are characteristics which should be taken into account:
• If the motor has slip, the safe speed estimate differs from the drive actual motor
shaft speed roughly the amount of the slip. The actual difference depends on the
load. See the graph below which illustrates the effect of the slip.
• When 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.
• If the motor shaft speed needs to be known also in cases where the drive is not
modulating, the safe speed estimation is not suitable for the application.
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
define monitoring limits for the safety functions. Otherwise it is possible that
unnecessary monitoring limit hits occur.
It is highly recommended to perform the Normal motor identification run of the drive in
the typical motor operating conditions (e.g. shafts connected to motors, nominal
temperature). This makes it possible to create the most accurate motor model for the
speed estimation. If the Normal ID run is not possible, do the Reduced or Standstill
identification run. For more information, see
ACS880 primary control program
firmware manual (3AUA0000085967 [English]).
The safe speed estimation can only be calculated when the drive is modulating.
When the drive stops the modulation, the safe speed estimation shows 0 rpm.
Because of this main principle, it is a must that the motor speed starts to slow down
by coasting when the power is switched off. If the motor is not decelerating fast