Siemens simatic c7-621 Hardware Installation Manual page 85

Figure 7-1 shows the connection of isolated sensors to a non-floating analog
input.
Figure 7-1
Non-Isolated Non-isolated sensors are connected to ground locally. Due to local conditions
Sensors or noise, potential differences (static or dynamic) can occur between the
locally distributed measuring points. To avoid these potential differences, you
should install equipotential bonding cables between the measuring points.
Potential differences U
measuring cables AIx-M of the input channels and the reference point of the
measuring circuit M. This potential difference must not exceed the maximum
permitted value. If it is possible that this will exceed the maximum permitted
value for U
AIx-M must be connected to M.
C7-621 / C7-621 AS-i Control Systems
C79000-G7076-C621-01
Analog inputs
AI1-U
+
U
AI1-M
Isolated
-
AI2-U
sensors +
U
AI2-M
-
Recommended
U
CM
connection
L+
Input 24V DC
M
NC
NC
Functional ground
Connection of Isolated Sensors to a Non-Floating Analog Input
(static or dynamic) can also occur between the
CM
or if you cannot measure the potential difference exactly,
CM
C7-621 Analog I/Os
C7-621
ADC
Logic
.
.
.
M
Grounding bar
C7-CPU
7-3