Forced Checking Procedure Of Spl Signals - Siemens SINUMERIK 840D sl Function Manual

8.1.2

Forced checking procedure of SPL signals

Fundamentals
Safety-related input/output signals including the connecting cables to the I/O (peripherals) and
the sensors and actuators connected to them must always be subject to a forced-checking
procedure (see Chapter "Forced checking procedure (Page 82)").
The scope of the forced checking procedure should be implemented corresponding to the
subsequent conditions.
This means that the selection of a suitable forced checking procedure concept depends on
the specific application and the specific sensor and/or actuator; this decision must be made
by the user. In this scope, the user must configure the forced checking procedure.
SPL signals
The forced checking procedure of SPL signals is a part of the SPL functionality (see Chapter
"Safe programmable logic (Page 256)").
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 acceptance test, the long-term
reliability of this function, verified using an acceptance test, can be ensured:
● External inputs/outputs
The external inputs/outputs of the SPL ($A_INSE or $A_OUTSE) must be subject to a
forced checking procedure to ensure that faults do not accumulate over a period of time
which would mean that both monitoring channels could fail.
● Internal inputs/outputs
Internal inputs/outputs ($A_INSI, $A_OUTSI), markers ($A_MARKERSI) etc.
($A_TIMERSI) do not have to be subject to a forced checking procedure.
It will always be possible to detect an error at these locations due to the differing two-channel
responses of the external inputs/outputs or the NCK/drive monitoring channels; crosswise
data comparison is carried out at both ends of the response chain to detect any errors.
Test signals
"3-terminal concept"
● If an input signal ($A_INSE) is, for example, evaluated through two channels, then 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.
● 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 simultaneous test in both
channels allows the correct functioning in both channels to be checked using one feedback
signal.
Safety Integrated
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
Connecting sensors and actuators
8.1 Safety-related input/output signals
177