Forced Checking Procedure - Siemens SINUMERIK 840D sl Function Manual

03.06
5.3

Forced checking procedure

Forced checking procedure, general (extract from /6/)
"...A forced checking procedure must be carried-out for all static (steady-stage)
signals and data. Within the required time (8 h), the state must change from a log-
ical 1 to a logical 0 – or vice versa. If the state remains static in a fault situation,
then this is detected at the latest as a result of this forced checking procedure and
the subsequent comparison.
A forced checking procedure must be used, e.g. for components that are required
to stop a process (e.g. contactors and power semiconductors) – the so-called shut-
down path and for the shutdown condition. Generally, it is not possible to test a
shutdown condition, e.g. violation of a limit value criterion, using other methods
such as e.g. crosswise data comparison, when the machine is in an acceptable
(good) condition. This also applies to errors along the entire shutdown path includ-
ing associated hardware and software and circuit-breakers.
By integrating a test stop every eight hours with a comparison and expected sta-
tus, faults can also be detected when the machine is in an acceptable (good) con-
dition...."
(Comment: Acceptable (good) condition means that there are no machine faults
that are apparent to the operator).
Forced checking procedure with Safety Integrated
The forced checking procedure is used to detect faults/errors in the software and
hardware of the two monitoring channels. In order to do this, the safety-related
parts in both channels must be processed at least once during a defined period in
all safety-related branches. Any faults/errors in the monitoring channel would
cause deviations and will be detected by the cross-wise data comparison.
The forced checking procedure of the shutdown path (test stop) must be initiated
by the user or integrated in the process as an automatic procedure, e.g.:
S When the axes are stationary after the system has been powered-up
S When the protective door is opened
S In defined cycles (e.g. every 8 hours)
S In the automatic mode, dependent on the time and event.
The forced checking procedure also includes testing the safety-related sensors
and actuators at the safety-related inputs/outputs. In this case, the entire circuit
including the "safe programmable logic" (SPL) is tested to ensure that it is correctly
functioning (see Subsection 7.1.2 "Forced checking procedure of SPL signals").
© Siemens AG, 2006. All rights reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 03.2006 Edition
Basics on the Safety Functions Integrated in the System/Drive
5.3 Forced checking procedure
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