Siemens SIMATIC ET 200S Installation And Operating Manual page 37

Requirements for the Duration of Sensor Signals
Warning
Observe the following requirements for sensor signals:
•
•
Reliable acquisition by the F-DI module
The following table lists the minimum duration of the sensor signals for the F-DI module. This
depends on the parameter settings for the short-circuit test and the input delay in
Table 4-2
Short-Circuit Test Parameter
Reliable acquisition by the safety program on the F-CPU
You will find information on the times necessary for correct acquisition of the sensor signals
in the safety program in
SIMATIC S7
Additional Requirements for Actuators
Fail-safe modules test the outputs in regular intervals. To do so, the F-module briefly
switches off activated outputs. The test pulses have the following duration:
• Dark period < 1 ms
Rapid response 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).
Warning
If the actuators are operated at voltages higher than 24 VDC (for example, 230 VDC) or if
the actuators clear higher voltages, safe isolation must be ensured between the outputs of a
fail-safe output module and the components carrying a higher voltage (in accordance with
EN 50178).
This is generally the case for relays and contactors. Particular attention must be paid to this
aspect for semiconductor switching devices.
ET 200S Distributed I/O System - Fail-Safe Modules
Hardware Installation and Operating Manual, 07/2005, A5E00103686-04
In order to guarantee accurate detection of the sensor signal by the F-DI module, you must ensure
that the sensor signals have a particular 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.
Minimum Duration of the Sensor Signals to Allow Correct Acquisition by the F-DI Module
Deactivated
Activated
"Fail-Safe Modules"
.
4.5 Requirements for Sensors and Actuators
Assigned Input Delay
0.5 ms 3 ms
7 ms 9 ms
7 ms 12 ms
in the system description
Wiring and Fitting Modules
STEP 7
15 ms
23 ms
37 ms
Safety Engineering in
.
4-7