Siemens SINUMERIK 840D sl Function Manual page 169

03.06
Trigger/test
The timer or event controlled triggering of the forced checking procedure is activa-
ted in one channel by the PLC.
If errors are detected, the PLC user program should respond by initiating an exter-
nal "STOP D/E" and switching the external SGAs into a safe state.
Notes to avoid errors
1. A "2-terminal concept" in which a single-channel net (useful) signal is to be
subject to a forced checking procedure using a single-channel test signal is
not permitted. In this case, the two-channel SPL structure would be worthless
and crosswise data comparison would have no effect.
The following are permitted:
S A "full 4-terminal concept for sensors" (two-channel test signal for a two-
channel useful [net] signal),
S the "3-terminal concept for sensors/actuators" recommended above,
S a "2-terminal concept for sensors without test signals", if the two-channel net
(useful) signal to be tested automatically changes its level dynamically as a
result of the process – e.g. for the input signals of a protective door,
S a "2-terminal concept for sensors without test signals", if the sensor is a
safety-relevant component, e.g. light curtains,
S a "2-terminal concept for actuators without test signals", if the actuator is a
safety-relevant component, e.g. safety valves,
S a "2-terminal concept for actuators without test signals" if the feedback si-
gnal can be checked using other useful signals - e.g. for a valve that indi-
rectly switches a BERO via the process and this is available for evaluation,
S a "2-terminal concept for actuators without test signals" if the function of the
mechanical system can be checked using other useful signals – e.g. for a
brake that is checked using a separate brake test.
2. The signals "external STOPs" are processed internally in a special way:
S In order to increase the level of security that a requested "external STOP"
actually takes effect, the STOPs are internally exchanged between the two
channels. Failure of the stop control function in one channel does not cause
an error for these signals (in contrast to the mode changeover signals, e.g.
"SG/SBH active") in the crosswise data comparison.
While other signals can be subject to a forced checking procedure in parallel
and in both channels (and should be – in order to avoid errors being trig-
gered by the crosswise data comparison), the "external STOPs" must be
subject to a forced checking procedure one after the other in both chan-
nels.
© Siemens AG, 2006. All rights reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 03.2006 Edition
Connecting Sensors/Actuators
7.1 Safety-relevant input/output signals
7-169