Wiring and Fitting Modules
4.5 Requirements for Sensors and Actuators
ET 200S Distributed I/O System - Fail-Safe Modules
38
Installation and Operating Manual, 08/2008, A5E00103686-07
Duration Requirements for Sensor Signals
WARNING
Observe the following requirements for sensor signals:
•
In order to guarantee accurate detection of sensor signals by the F-DI module, you must
ensure that the sensor signals have a defined minimum duration.
•
Reliable pulse detection requires an interval between two signal changes (pulse
duration) greater than the PROFIsafe monitoring time.
Reliable detection by the F-DI module
The table below lists the minimum duration of sensor signals for the F-DI module. This
depends on the parameter settings made in
STEP 7 for the short-circuit test and the input
delay.
Table 4- 2
Minimum Duration of Sensor Signals to Allow Correct Detection by F-DI-Module
Programmed Input Delay
Short-Circuit Test Parameter
0.5 ms
3 ms
15 ms
Deactivated
7 ms
9 ms
23 ms
Activated
7 ms
12 ms
37 ms
Reliable Detection by the Safety Program on the F-CPU
Information about the times required for the reliable detection of sensor signals in the safety
program is available in
"Fail-Safe Modules" of the Safety Engineering in SIMATIC S7 system
description.
Additional Requirements for Actuators
The F-modules test the outputs at regular intervals. To do so, the F-module briefly switches
off the activated outputs. Duration of these test pulses:
●
Dark period < 1 ms
Rapid response actuators may briefly drop out 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 greater than 24 VDC (for example, 230 VDC) or if
the actuators switch 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
issue for semiconductor switching devices.
