Siemens Simatic S7-300

Priniples of analog value processing
4.7 Connecting loads/actuators to analog outputs
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
4-21
4.7.1 Connecting loads/actuators to voltage outputs
Connecting loads to a voltage output
Basically, you may choose between the 2-wire and 4-wire technique to connect loads to
voltage outputs. However, certain analog output modules do not support both connections.
4-wire connection of loads to a voltage output of an electrically isolated module
You can use the 4-wire technique to achieve a high accuracy at the load, by wiring the S-
and S+ sensor lines directly to the load. This results direct measurement and correction of
the voltage at the load.
Disturbance or voltage drops may lead to a potential difference between sensor line S- and
the reference circuit of analog circuit M
ANA
. This potential difference may not exceed the
permissible value. A negative influence on the accuracy of the analog signal is otherwise
inevitable.
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Figure 4-17 4-wire connection of loads to a voltage output of an electrically isolated analog output
module