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5
Safety function
The FORTiS-S FS encoder system shall provide a safe position when requested by the evaluation
unit.
The following restrictions apply to this claim:
X
The system installer must perform a verified commissioning test during installation.
X
The system repairer must perform a verified commissioning test following replacement of a system
part.
X
The maximum request rate supported is 32 kHz.
X
Electrical errors for the BiSS Safety protocol are detected by the evaluation unit comparing CPW and
SPW content. See BiSS Safety for RESOLUTE encoders data sheet (Renishaw part no. L-9517-9884)
for more information.
X
Electrical errors for the Siemens DRIVE-CLiQ protocol are detected by the evaluation unit comparing
POS1 and POS2 content. See the relevant Siemens AG evaluation unit manual for more information.
X
When installed correctly, the FORTiS‑S FS encoder system has a mechanical safe position of ±1 mm.
5.1 Fault exclusions
The following will invalidate the Functional Safety certification of the FORTiS-S FS encoder system:
X
Faults caused by cutting and reconnecting the cable or the use of a non-Renishaw cable that is not
approved.
X
Incorrect installation.
X
Dismantling.
X
Operating the system outside of the limits specified in this installation guide.
5.2 Failure modes effects and diagnostics analysis
All diagnosed failure modes are detected immediately except for a position discrepancy between the two
measurement methods which is detected within 375 μs.
See
'Functional Safety data declaration' on page 4
NOTE: For the purposes of the FMEDA calculation the following conditions have been assumed:
Method: SN29500-2005-1
Environment: Ground mobile
5.3 Installation
For the safety function to be valid the instructions detailed in this installation guide must be followed.
5.4 Commissioning test
The following test MUST be performed when commissioning the FORTiS-S FS encoder system and after
any repair or maintenance of the system.
Resolution check
Move the axis by a known distance and confirm that the position changes
as expected. The tolerance for raising a fault condition is relative to the safe
position determined by the system manufacturer.
Original instructions
for a summary of the FMEDA.
Temperature: 85 °C
5.5 Evaluation unit monitoring
To achieve full system integrity the evaluation unit must continuously monitor the error condition of the
FORTiS-S FS encoder system, and in the case of fault detection place the system into a safe state
within the process safety time.
NOTES:
X
The evaluation unit must have its Functional Safety functions enabled (as often it is a configuration
parameter to turn on Functional Safety functionality) and must respond correctly to a FORTiS‑S FS
encoder system position error flag.
X
A persistent fault condition may indicate a hardware failure of the FORTiS-S FS encoder system
or an installation problem.
5.6 Maintenance
The maintenance check intervals will be defined by the system manufacturer according to their risk
assessment. There are no user-serviceable parts within the FORTiS-S FS encoder system.
The following maintenance actions are advised:
X
Check the extrusion screws and readhead retaining screws are correctly tightened.
X
Check for worn or damaged cables and connectors.
X
Check the cable connectors are correctly tightened/located.
X
Check the air supply fitting is correctly tightened and the air hose is correctly fitted.
X
When the DRIVE-CLiQ interface is used check the retaining screws are correctly tightened.
5.7 Repair
X
Repair of the FORTiS-S FS encoder system is only by replacement of
X
The replacement parts must have the same part number as the original parts.
X
The repaired encoder system must be installed and commissioned in accordance with the
'Commissioning test' above.
X
In the event of failure the affected parts should be returned to Renishaw for further analysis.
X
Using damaged parts invalidates the Functional Safety certification.
5.8 Proof testing
It is the responsibility of the system manufacturer to define any proof testing of the system. Due to the
diagnostic coverage (DC) and safe failure fraction (SFF) required to achieve SIL2, the encoder can only
support continuous demand use.
parts.
5
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