Siemens SIMATIC Operating Instructions Manual page 31

Requirements for the Duration of Sensor Signals
Note the following requirements for sensor signals:
• In order to guarantee accurate detection of sensor signals by the F-DI/F-DO module
• In order for pulses to be detected with certainty, the time between two signal changes
Reliable Detection by the F-DI/F-DO Module Inputs
The following table lists the minimum duration of the sensor signals for the F-DI module. The
minimum duration depends on the parameter settings for the short-circuit test and the input
delay in
Table 4-1
Electronic module
8/16 F-DI
4/8 F-DI/4 F-DO
F-Switch
PROFIsafe
Reliable Detection By the Safety Program in the F-CPU
For information about the times for proper detection of sensor signals in the safety program,
refer to
Additional Requirements for Sensors
General rule: A single-channel sensor is sufficient to achieve SIL2/Category 3. However, the
sensors must be connected using two channels in order to achieve SIL3/Category 4.
However, to achieve SIL2/Category 3 with a single-channel sensor, the sensor itself must be
SIL2/Category 3-capable, otherwise the sensors must be connected using two channels in
order to achieve this safety level.
Additional Requirements for Actuators
Fail-safe output modules test the outputs at regular intervals. For this purpose, the F-module
briefly switches off enabled outputs. The test pulses have the following duration:
● Dark period < 1 ms
Fast-acting actuators can drop out briefly during the test. If your process does not tolerate
this, you must use actuators with a sufficient lag (> 1 ms).
ET 200pro Distributed I/O System - Fail-Safe Modules
Operating Instructions, 05/2007, A5E00394073-02
WARNING
inputs, you must ensure that the sensor signals exhibit a certain minimum duration.
(pulse duration) must be greater than the PROFIsafe monitoring time.
STEP 7
.
Minimum Duration of Sensor Signals for Proper Detection by an F-DI Module
Short-circuit test parameter
"Fail-Safe Modules"
4.4 Requirements for Sensors and Actuators
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Safety Engineering in SIMATIC S7
in the
Assigned input delay
0.5 ms 3 ms
10 ms 13 ms
10 ms 18 ms
11 ms 13 ms
11 ms 20 ms
- 14 ms
- 27 ms
system description.
Wiring
15 ms
25 ms
56 ms
25 ms
57 ms
-
-
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