Siemens SIMATIC User Manual

Principles of analog value processing
4.2 Wiring and connecting transducers to analog inputs
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
239
4.2 Wiring and connecting transducers to analog inputs
Transducers which can be wired and connected to analog inputs
You can wire and connect the following transducers to the analog input modules, depending
on the type of measurement:
● Voltage transducers
● Current transducers
– As 2-wire transducer
– As 4-wire transducer
● Resistors
● Thermocouples
Cables for analog signals
Always use shielded twisted-pair cables to wire analog signals. This reduces interference.
Connect both ends of the analog cable shield to ground.
Any potential difference between the cable ends may cause an equipotential current on the
shield and disturbance on analog signals. Avoid this effect by means of low-impedance
equipotential bonding. Ground only one end of the shielding.
Electrically isolated analog input modules
Electrically isolated analog input modules are not electrically interconnected at the reference
point of the measuring circuit (M
ANA
and/or M) and the M terminal of the CPU/IM153.
Always use electrically isolated analog input modules if there is any risk of potential
difference V
ISO
developing between the reference point of measuring circuit (MANA and/or
M-) and the M terminal of the CPU/IM153 .
You can prevent the potential difference V
ISO
from exceeding limits by means of
equipotential interconnection of terminals M
ANA
and M of the CPU/IM153.
Non-isolated analog input modules
Non-isolated analog input modules require a low-impedance connection between the
reference point of measuring circuit M
ANA
and the M terminal of the CPU or interface module
IM 153. Interconnect terminals M
ANA
with M of the CPU or interface module IM 153. Any
potential difference between M
ANA
and M of the CPU or interface module IM 153 may corrupt
the analog signal.
Limited potential difference CMV
The permissible potential difference U
CM
(CMV/Common Mode) may not be exceeded. A
CMV fault may develop between
● the measurement inputs (M+ / M-) and the reference potential of measuring circuit M
ANA
● between the measuring inputs.
The following diagrams show the measures to be taken when wiring transducers.

Siemens SIMATIC Specifications

General

Brand	Siemens
Model	SIMATIC
Category	Control Unit
Language	English