44 Overview
Safe position
With the FSO-21 module, FSE-31 module, safety encoder and PROFINET adapter
(FENA-21 or FPNO-21 module), it is possible to utilize safe position data via a safety
PLC. To use the safe position data, a PROFIsafe connection and the PS2-profile are
needed. See section FSO PROFIsafe profiles on page 201.
Note: With an HTL encoder, the position data can be lost with power loss, if there is a
failure in any of the devices in the safety chain, or the bit Speed_Pos_value_valid of
the PROFIsafe profile indicates invalidity. Rezeroing is needed to verify the position.
Motor speed feedback
FSO module needs motor speed feedback to perform safety functions. It can be
either a measured speed from a safety encoder or a safe speed estimate. With
FSO-12 module only safe speed estimate is available. FSO-21 module supports both
safe speed estimate and measured speed from an HTL safety encoder via the
FSE-31 encoder interface module. Depending of the motor speed feedback, safety
functions operate slightly differently (for example, when the indications turn on and
off) due to inaccuracy in safe speed estimate. The feedback type has also an effect
on how the safety functions are configured. See chapter Safety functions for more
information on the difference between the measured speed feedback (encoder) and
safe speed estimate.
Note: With safe speed estimate, the FSO module and the drive motor control have an
independent motor model of their own. The accuracy of these two speed estimates
can differ from each other, especially in the low speed region.
Safe speed estimate
Note: Safe speed estimate cannot be used with a DCS880 drive.
With safe speed estimate, the FSO module uses the drive electrical output frequency
measurement to estimate the motor speed. To have the most accurate motor model
for the safe speed estimation, it is necessary to set the motor nominal values to
parameters FSOGEN.21 and FSOGEN.22.
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 312.
It must be considered in the risk assessment of the application whether the safe
speed estimate can be used.
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