Overview 43
Safety encoders
Safety pulse encoders are connected to the FSE-31 pulse encoder interface module.
The safety pulse encoder delivers pulses to the FSE-31 module which delivers safe
speed, direction and position information to the FSO-21 module. The safety encoders
supported by the FSE module must fulfill these requirements:
• It must have differential outputs (two quadrature-signals and one rotation mark
signal, each in its normal and complement format).
• It must have sufficient auto-diagnostics and mitigations against environmental
variations for the intended PL and/or SIL.
• It must indicate its faults either by setting its outputs to the hi-Z state (“floating” the
outputs) or by setting its complement outputs to identical states.
Note: It can be useful for the argumentation of the validity of the above that the
encoder is approved for safety applications. When the FSE-31 module and a safety
encoder are used in a safety function with a SIL/PL requirement, the safety encoder
must be SIL/PL classified. The user must make sure that the SIL/PL capability of the
safety encoder and the complete safety function meets the required SIL/PL.
With ACS880, two safety functions, SDI and STO with speed limit activated SBC,
require a safety encoder. With DCS880, the safe speed estimate cannot be used, and
it is recommended to always use an FSE-31 module with a safe encoder together
with the FSO-21 module. The following table shows the requirements in detail.
1)
POUS does not use motor speed data.
2)
With or without time-controlled SBC.
3)
Only immediate STO (with or without time-controlled SBC).
Note: The encoder used must be approved for safety applications.
Safety function ACS880 DCS880
Can be used with
safe speed
estimate or with a
safety encoder
Can only be used
with a safety
encoder
Can be used
without encoder
Can only be used
with a safety
encoder
STO (with or
without SBC)
xx
2)
SS1 x x
SSE x x
3)
SLS x x
varSLS x x
SMS x x
SSM x x
SDI x x
STO with speed
limit activated SBC
xx
POUS
1)
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