8
Error behavior
8.1
General
A non-hazardous failure of the device occurs:
•
If the safety-related function is not fulfilled and the device changes to one of the
safety-related states.
•
If the device changes to one of the safety-related states when an internal error is
detected.
A hazardous undetected failure occurs:
•
If a safety-related function is fulfilled and the device does not change to one of the
safety-related states.
•
If the safety-related measured value deviates by more than the defined uncer‐
tainty.
8.2
Internally detected errors
The device itself, i.e., based on the internal diagnostics performed in the device, has
a diagnostic coverage (DC) of zero according to EN ISO 13849-1:2015. By taking into
account further external diagnostics and thus supplementing the internal diagnostics,
it is possible however to achieve a DC of 60% in a higher-level system. The required
combination of diagnostic measures to achieve a DC of 60% are described in
in the safety-related system", page 51
. This makes it necessary, however, to include
an external downstream controller when determining the diagnostic coverage. This
controller plays a significant role in detecting the errors and enabling a DC of 60% to be
achieved. The effectiveness of the required diagnostics must always be evaluated and
validated by the system integrator for the specific application.
8.3
Internally undetected errors and faults
The device itself will
not reliably detect
the following errors and faults as a minimum:
•
Input:
Short to ground, wire break, short-circuit, cross circuit at the digital input.
•
Outputs:
Short to ground, wire break, short-circuit, cross circuit at the digital
outputs. This also applies in the case of incorrect wiring of the connection pins.
•
Measurement data interfaces:
Wire break, short-circuit, cross-circuit and EMC
influences, with the effect that corrupted or no measurement data are transmitted
to the downstream controller.
•
Display elements / LED:
Failure of the status indicators for operational status and
the digital outputs.
•
Contamination:
Contamination of the optics and/or the front screen, causing
impairment, reduction or complete loss of detection capability, and the device no
longer being able to perform the safety function.
•
Ambient light:
Malfunctions due to faults of other devices and light sources at the
level of the optical receiver unit, causing impairment, reduction or complete loss of
detection capability, and the device no longer being able to perform its function.
•
Incorrect measurements:
Measurement of objects with edges and/or corners at
the measurement spot and/or which are moving too quickly (determined by the
measurement procedure) can result in incorrect distance values, causing impair‐
ment, reduction or complete loss of detection capability, and the device no longer
being able to perform the safety function.
8
ERROR BEHAVIOR
46
O P E R A T I N G I N S T R U C T I O N S | DT35S
8027663//2022-08-04 | SICK
Subject to change without notice