Analog Modules
4-46
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Abbreviations and mnemonics used in the figures below
The abbreviations and mnemonics used in the figures below have the following
meanings:
M +: Measuring lead (positive)
M–: Measuring lead (negative)
M
ANA
: Reference potential of the analog measuring circuit
M: Ground terminal
L +: Terminal for 24 VDC supply voltage
U
CM
: Potential difference between inputs and reference potential of
the M
ANA
measuring
circuit
U
ISO
: Potential difference between M
ANA
and M terminal of CPU
I +: Measuring lead for current input
U +: Measuring lead for voltage input
Connecting isolated measuring sensors
Isolated sensors are not connected with the local ground potential (local ground).
They can be operated free of potential.
With isolated sensors, potential differences might arise between the different
sensors. These potential differences can arise as a result of interference or the
local distribution of the sensors.
To prevent the permissible value for U
CM
being exceeded when used in
environments with a high level of EMC interference, we advise you to connect M–
with M
ANA
.
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