6
GFK-2731
Chapter 6 Connection examples for safe outputs
6-5
6.4
Single-channel assignment of safe outputs
Figure 6-2
Single-channel assignment of outputs
K1 (R) and K2 (R) represent the positively driven N/C contacts for monitoring the state of
the relay (readback contacts). Connect these contacts via safe digital inputs. Evaluate the
readback and thus the state of the switching elements in the safety logic.
Basic specifications
–
In order to achieve Cat. 3 or PL d with single-channel assignment of the outputs, a
two-channel actuator must be used. The two-channel operation of the actuator with
the corresponding connection is represented on a gray background.
–
The failure detection time is 20 ms. This means that high pulses of this width can
occur in the event of an error.
If the application responds to these pulses, use the two-channel assignment of the
outputs.
WARNING: Loss of safety function
Connect the actuator ground directly to terminal point GND of the safety module. An
external ground may not be used.
73421005
K2 (R)
K1 (R)
K1
K2
OUT1_Ch1
GND
M
Actuator
Single-channel
Two-channel
Achievable SIL/SIL CL/Cat./PL
SIL 2/SIL CL 2/Cat. 2/PL c
SIL 2/SIL CL 2/Cat. 3/PL d
WARNING: Loss of electrical and functional safety
–
To achieve the specified safety integrity level, please refer to "Measures required to
achieve a specific safety integrity level" on page 6-3.
–
Please note that in order to achieve the specified PL, the actuator must have a
medium level of diagnostic coverage (90% to 99%) and medium MTTFd. A high level
of diagnostic coverage (> 99%) is recommended for the application according to
PL d.
–
To achieve Cat. 3 and PL d the test pulses must be enabled.
–
Use actuators that can achieve the required safety integrity level.
–
Evaluate the readback contacts to achieve the corresponding safety integrity level.
