Siemens SIMATIC S7-300 Module data - Connecting Loads to a Voltage Output of an Isolated AO over a Four-Conductor Connection

Analog Modules
4-68
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Connecting Loads to a Voltage Output of an Isolated Module over a
Four-Conductor Connection
A high accuracy at the load can be achieved through the four-conductor
connection. You must therefore connect the sensor leads (S– and S+) directly to
the load. The voltage is thus measured and corrected directly at the load.
Interferences or a voltage drop can result in a potential difference between the
sensor lead S– and the reference circuit of the analog circuit M
ANA
. This potential
difference must not exceed the permissible value. If the permissible potential
difference is exceeded, the accuracy of the analog signal is impaired.
M
L+
DAC
R
L
Q
V
M
ANA
M
internal
L+
M
Ground bus
CPU
S+
S–
U
ISO
Backplane
bus
Logic
Figure 4-28 Connecting Loads to a Voltage Output of an Isolated AO over a Four-Conductor Connection