Siemens SINUMERIK 840D sl Function Manual page 168

Connecting Sensors/Actuators
7.1 Safety-relevant input/output signals
SPL signals
The forced checking procedure of SPL signals is a part of the SPL functionality
(see Section 7.3 "Safe programmable logic (SPL))".
Once the external safety circuit has been wired, a two-channel SPL has been
created and the relevant safety functions configured and checked with an accep-
tance test, the long-term reliability of this function, verified using an acceptance
test, can be ensured:
S External inputs/outputs
The external inputs/outputs of the SPL ($A_INSE or $A_OUTSE) must be sub-
ject to a forced checking procedure to ensure that faults do not accumulate over
a period of time which would mean that both monitoring channels could fail.
S Internal inputs/outputs
Internal inputs/outputs ($A_INSI, $A_OUTSI), markers ($A_MARKERSI) etc.
($A_TIMERSI) do not have to be subject to a forced checking procedure. It will
always be possible to detect an error at these locations due to the differing two-
channel responses of the external inputs/outputs or the NCK/drive monitoring
channels; crosswise data comparison is carried-out at both ends of the res-
ponse chain to detect any errors.
Test signals
"3-terminal concept" (see Subsection 7.1.3 "Connecting sensors – actuators
using the 3-terminal concept"):
S If an input signal ($A_INSE)is, for example, evaluated through two channels,
the associated test output signal can be implemented using one channel. It is
extremely important that the input signal can be forced/changed and checked in
both channels.
S In the same way, the assigned test input signal for two-channel output signals
($A_OUTSE) can be implemented in one channel if it is connected according to
the following rule:
The test input signal may only return an "OK" status ("1" signal level) if both
output signals function (i.e. both monitoring channels have output a "0"). A si-
multaneous test in both channels allows the correct functioning in both chan-
nels to be checked using one feedback signal.
7-168
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 03.2006 Edition
© Siemens AG, 2006. All rights reserved
03.06