Siemens SIMATIC PCS 7 Operating Manual page 61

F-short-circuit detection
If a short-circuit is detected, a diagnostics interrupt will be triggered in the CPU and a
corresponding process control message will be sent on the OS.
Advanced short-circuit diagnostics can be triggered when required by means of additional
limit-value monitoring.
Measurement type
The measurement type depends on the operating mode selected.
The operating mode can be selected for each channel. In safety mode the following
measurement types are available:
● "2DMU" or "4DMU" for current measurements. (4 to 20mA)
● "Deactivated": The channel is not processed by the module.
Measuring range
The selection options in the measuring range field vary depending on the selected mode
(safety mode activated or deactivated) as well as the measurement type. If a channel is
deactivated, it will not be possible to select a measuring range.
Note
If you are using Marshalled Termination Assemblies (MTAs), you should select 4DMU for the
configuration, since the supply is provided via the MTAs.
Note
In safety mode, only the 4 to 20 mA measuring range is permitted. In this measuring range, a
current of < 3.6 mA will produce a wire-break signal. If, however, the type of sensor you are
using (e.g. a gas sensor) means that you do need to process signals that fall below this
range, you can deactivate F wire-break detection. In this case, a current of < 1.18 mA will
produce an underflow message.
For more information, please refer to the following FAQ: "How can process signals that are
less than 4 mA be used with a 4 to 20 mA analog input module (F technology)?"
(https://support.industry.siemens.com/cs/ww/en/view/23707365).
Compendium Part B - Process Safety (V8.2)
Operating Manual, 07/2016, A5E35031794-AB
Configuring S7F/FH hardware
6.4 Setting system parameters for F-signal modules
61