Siemens SIMATIC ET 200S Installation And Operating Manual page 149

Connecting capacitive loads
If the electronic outputs of the EM 4 F-DO DC24V/2A PROFIsafe are connected to loads that
require little current and have capacitance, this can lead to the "short circuit" error message.
This is required because the capacitance cannot be sufficiently discharged during the set
self-test readback time.
The following figure shows the typical curves of the selectable readback times indicating the
relationship between load resistance and connectable load capacitance.
Figure 7-40
Remedy:
1. Determine the load current and capacitance of the load.
2. Determine the operating point in the figure above.
3. If the operating point is above the curve, you must increase the load current until the new
ET 200S Distributed I/O System - Fail-Safe Modules
Hardware Installation and Operating Manual, 07/2005, A5E00103686-04
Relationship between Load Resistance and Switchable Load Capacitance for
EM 4 F-DO DC24V/2A PROFIsafe
operating point is below the curve by connecting a resistor in parallel.
7.6 4 F-DO DC24V/2A PROFIsafe digital electronic module
Fail-Safe Modules
7-89