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Safety function
The TONiC FS system provides 1 Vpp (nominal) sine and cosine outputs, where the sine and cosine
outputs are 90° phase shifted, in order for the evaluation unit to perform incremental counting and
thereby confirm machine position is within safe limits.
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
When installed correctly, the TONiC FS system shall have mechanical safe position not exceeding 2.5°.
NOTE: Thermal expansion effects of the scale and readhead mounting tolerances are excluded from the
mechanical safe position.
X
The TONiC FS system includes no self-diagnostic function.
NOTE: Faults are detected only by the evaluation unit monitoring. When errors are detected it is the
responsibility of the system manufacturer to place the system into a safe state.
Fault exclusions
The following will invalidate the Functional Safety certification of the TONiC FS system
X
Faults caused by cutting and reconnecting the readhead cable or extending the readhead cable.
X
Incorrect installation of the readhead.
X
Incorrect installation of the scale.
X
Dismantling of the TONiC readhead or the Ti or DOP interfaces.
X
Operating the system outside of the limits specified within this installation guide.
Failure modes
Failure modes are detected by evaluation unit monitoring. See
for a summary of the FMEDA.
NOTE: For the purposes of the FMEDA calculation, the following conditions have been assumed:
Method:
SN29500
Environment:
Installation
For the safety function to be valid the instructions detailed in this installation guide must be followed.
Commissioning test
The following check must be performed when commissioning the TONiC FS system and after any repair of
the system.
NOTE: Repair is by replacement of system parts only.
Axis movement check
Move the axis over its full travel to verify the following:
X
Position output is correct within a tolerance of ±10%.
X
Direction of movement is correct.
X
The signal amplitude for both sine and cosine signals falls within the limits
defined in 'Evaluation unit monitoring'.
TONiC RESM20 Functional Safety installation guide and safety manual
(see page
'Functional Safety data declaration' on page 2
Ground mobile
Temperature:
85 °C
Evaluation unit monitoring
To achieve full system integrity the evaluation unit must continuously monitor the analogue outputs and,
in the case of fault detection, place the system into a safe state within the process safety time.
Signal amplitude check
Sine/cosine cross check
Following error check
NOTES:
X
The evaluation unit must achieve medium diagnostic coverage (≥90%) according to ISO 13849.
4):
X
Improper setting of the switching thresholds and hysteresis in signal evaluation can result in incorrect
determination of direction of rotation, position or speed.
X
A persistent fault condition may indicate a hardware failure of the TONiC FS system or an
installation problem.
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 readhead and interface.
The following maintenance actions are advised:
X
Check the readhead to bracket screws are correctly tightened.
X
Check for worn or damaged cable connecting the readhead to the interface.
X
Check that the scale has not been damaged or contaminated. If required, clean the system using
approved solvents
(see 'Storage and handling' on page
NOTE: Do not retighten the screws securing the encoder ring as this will change the ring settings.
Repair
The replacement parts must have the same part number as the original parts. The new system must be
installed and commissioned in accordance with the 'Commissioning test'. In the event of failure the affected
parts should be returned to Renishaw for further analysis. Using damaged parts invalidates the Functional
Safety certification.
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.
Original instructions
Nominal signal amplitude value is 1 V, indicating full signal strength where
√ (sine
+ cosine
) = 1 V. A fault condition must be asserted if the analogue
2
2
output is ≤0.7 V and ≥1.35 V.
Sine and cosine signals must be evaluated separately and the results
compared. A fault condition must be asserted if the phase shift is incorrect
with reference to the safe position limit for the system,
specifications' on page
22.
Following error is defined as the difference between the expected position
and position feedback. A fault condition must be asserted if the following error
exceeds the safe position limit for the system.
5).
see 'Output
3
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