Siemens SINAMICS G130 Manual page 52

System Features
3.6 Residual risk
Within a single-encoder system:
a) a single electrical fault in the encoder
b) encoder shaft break, (or detachment of the encoder shaft coupling), or a loose encoder
housing will cause a static state of the
encoder signals (i.e. they no longer follow the movement while still returning a correct
level), and thus do not detect this fault while the drive is in stop state (for example, drive in
SOS state).
Generally, the drive is held by the active closed-loop control. With closed loop control, it is
conceivable that vertical (suspended) drives in particular can move without their motion
being detected.
The risk of an electrical fault in the encoder as described under a) is only present for few
encoder types with specific function principle (for example, encoders with microprocessor
controlled signal generation such as the Heidenheim EQI, Hübner HEAG 159/160, or AMO
measuring systems with sin/cos signals).
The risk analysis of the machine manufacturer must include all of the faults described
above. Additional safety measures have to be taken for drives with suspended/vertical or
dragging loads in order to exclude the faults described in a), for example:
• Use of an encoder with analog signal generation or
• Use of a two-encoder system
and in order to exclude the fault described in b):
• Execution of an FMEA regarding encoder shaft breakage (or detachment of the encoder
• implementation of a two-encoder system (the encoders should not be mounted on the
52
WARNING
shaft coupling), and a solution to prevent loose encoder housings, integration of a fault
exclusion process, e.g. in accordance with CDV IEC 61800-5-2, or
same shaft).
Safety Integrated
Function Manual, 05/2010, A5E03264275A