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10/23/2019
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2.5 Safety functions of the fail-safe processing unit
The
S
afety
C
omputer
S
ystem (SCS), to which the measuring system is connected,
must perform the following safety checks.
With regard to "Single fault safety" and "Ideal error detection" please see IFA directive
"GS-IFA-M21". This can be downloaded under the following link:
www.tr-electronic.com/f/zip/TR-E-TI-DGB-0107
To enable the correct measures to be taken in the case of error, the following
applies:
●
Safe state – passive, only for measuring system variant 1
In passive safe state the measuring system does not output any valid
SIN±/COS± – signals to the downstream fail-safe processing unit. The processing
unit detects the error through evaluation of the annulus relationship SIN(x)
2
+
COS(x)
2
= 1. If the result is outside the tolerance range, the incremental data are
evaluated as unsafe. The downstream fail-safe processing unit has an ideal error
detection.
●
Safe state – active, only for measuring system variant 2
In active safe state the signal outputs are switched to tri-state. The processing
unit detects the error via an implemented cable breakage detection.
2.5.1 Mandatory safety checks / measures
Measures for commissioning, changes
SCS error reaction
Check that the desired automation task is executed as
required.
STOP
Check by the SCS
SCS error reaction
Check of incremental data according to the present
automation task and safety function.
STOP
Two-channel monitoring of incremental outputs for cable
breakage.
For tri-state state
-> STOP
Only for variant 1
Evaluation of the condition SIN(x)
2
+ COS(x)
2
= 1. The number
of checks / revolution corresponds to the number of
periods/revolution: 1024, 2048 or 4096
For the safety functions SDI, SS1, SS2, SOS, SSR, SSM an
annulus monitoring with DC = 90 % is required.
For the SLS safety function a two-channel evaluation of the
frequency from (SIN/COS) with a DC of 90 % is required.
If outside tolerance
-> STOP
Only for variant 2
A cable break detection is required for the evaluation of the
square pulse signals.
In the safe state, the output drivers are in tri-state
(high-resistance state).
If a cable break is
detected
-> STOP
Only for variant 2
Evaluation of the incremental data in differential mode and
verification with respect to antivalence, quadrature and
against phase equivalence between channels A and B
If outside tolerance
-> STOP
