Wiring
4.4 Requirements for Sensors and Actuators
ET 200pro Distributed I/O System - Fail-Safe Modules
Operating Instructions, 05/2007, A5E00394073-02
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Requirements for the Duration of Sensor Signals
WARNING
Note the following requirements for sensor signals:
•
In order to guarantee accurate detection of sensor signals by the F-DI/F-DO module
inputs, you must ensure that the sensor signals exhibit a certain minimum duration.
•
In order for pulses to be detected with certainty, the time between two signal changes
(pulse duration) must be greater than the PROFIsafe monitoring time.
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
STEP 7.
Table 4-1
Minimum Duration of Sensor Signals for Proper Detection by an F-DI Module
Assigned input delay
Electronic module Short-circuit test parameter
0.5 ms
3 ms
15 ms
Disabled
10 ms
13 ms
25 ms
8/16 F-DI
Enabled
10 ms
18 ms
56 ms
Disabled
11 ms
13 ms
25 ms
4/8 F-DI/4 F-DO
Enabled
11 ms
20 ms
57 ms
Disabled
-
14 ms
-
F-Switch
PROFIsafe
Enabled
-
27 ms
-
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
"Fail-Safe Modules" in the Safety Engineering in SIMATIC S7 system description.
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).
