BBH SCU Series, Installation Manual

Page: 86 / 303

10
Safety-related characteristics
HB-37500-810-11-16F-EN SCU Installation Manual - Master and Slaves - SARC Page 86 of 303
Status: 09.06.2022
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Sensor PES Actuator
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Fig. 15: digital sensor one-channel
One-channel input element and two-channel processing at low to medium DC due to
two-channel signal processing and diagnostics by means of cyclical testing. PL / SIL
dependent on permissible fault exclusions and on the test rate of input element.
10.2.1.2. DC of digital sensors / inputs
The SCU modules ensure far reaching diagnostics functions for the input element. These
are carried out permanently or optionally (cross-shorting monitoring by means of pulse
identifier, cross comparison, 2- or multi-channel sensor with/without time-out, start-up
test).
Pernanently active diagnostics functions:
Cross comparison:
The SCU modules inputs are in general internally designed with two channels. The status
of input signals is permanently compared crosswise. Only with High signals in both partial
input systems the input is considered a High input, should the signal level deviate between
both channels, the input is set to Low state.
Dynamic test of the partial input system switching thresholds:
The switching thresholds for the detecting the High level are tested cyclically with a high
cycle rate. Falling below the defined threshold value a module triggers a module alarm.
Dynamic test of the input system ’s switchability :
The switchability of the input system to Low level is tested for all inputs with a high rate.
Falling below the defined threshold value a module triggers a module alarm.
Diagnostics functions that can be enabled by parametrization:
Cross circuit test:
The SCU modules have clock signal outputs, identified by an unabiguous signature. When
performing the cross-shorting test the switching elements of the digital sensors / input
elements are supplied with auxiliary voltage by the SCU unit via the clock signal outputs.
The signature is thus stamped on the High signal level of the sensors / input elements and
checked by the SCU assembly. With the signature test short-circuits and cross-shorting to
High signals can be recognized. With alternating use of the pulse signals of multi-contacts,