Siemens Simatic S7-400 - Manual (Page 263)

Analog Modules
5-47
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
5.10 Connecting Current Sensors
Note
The necessary connecting cables, which result from the potential connection of the
analog input module and the sensors, are not drawn in the figures shown below.
In other words, you must continue to take note of and implement Section 5.8 with
its generally applicable information for connecting sensors.
Abbreviations and Mnemonics Used in the Figures Below
The abbreviations and mnemonics used in the figures below have the following
meanings:
M +: Measuring line (positive)
M –: Measuring line (negative)
M
ANA
: Reference potential of the analog measuring circuit
M : Ground terminal
L +: Terminal for 24 VDC supply voltage
U
H
: Auxiliary supply
M
I+
: Current measuring line (positive)
M
V+
: Voltage measuring line (positive)
Supply Voltage of the Sensors
The two-wire transmitter receives its short-circuit-proof power supply via the
terminals of the analog input module.
This transmitter then converts the measured variable into a current.
Because the two-wire transmitter is supplied by the module, you must not ground
the M- cables.
Four-wire transmitters require a separate supply voltage U
H
(auxiliary supply).