Siemens SIMATIC C7-626, Installation, Assembly, Wiring

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6
6-2
C7-626 / C7-626 DP Control Systems
C79000-G7076-C626-01
6.1 Connecting Transducers to Analog Inputs
You can connect various types of transducers to the analog inputs:
S
Voltage transducers
S
Current transducers
To reduce electrical interference, you should use twisted-pair shielded cables
for the analog signals. The shield of the analog signal cables should be
grounded at both cable ends. If there are potential differences between the
cable ends, an equipotential bonding current can flow over the shield. This
can interfere with the analog signals. In such a case, you should ground the
shield at one end of the cable only.
The analog input is isolated and so there is no electrical connection between
the reference point of the measuring circuit M
ANA
and the M terminal of the
C7 power supply (see Figure 6-1).
A potential difference V
ISO
can occur between the reference point of the
measuring circuit M
ANA
and the M terminal of the C7. Make sure that V
ISO
does not exceed the permissible value. Where it is possible that the
permissible value might be exceeded (see technical specifications), establish
a connection between the M
ANA
terminal and the M terminal of the C7.
A potential difference V
CM
(common mode voltage) may occur between the
measuring line AIx-M of the input channels and the reference point of the
measuring circuit M
ANA
. However, this potential difference must not exceed
the permissible value. Where it is possible that the permissible value for V
CM
might be exceeded, or where you cannot determine the difference in potential
accurately, you must connect AIx-M to M
ANA
. Please observe this also for
the unused inputs.
The abbreviations used in Figures 6-1 to 6-3 have the following meanings:
AIx-X: Measuring line AIx-U or AIx-I
AIx-M: Reference potential of the measuring line
M
ANA
: Reference potential of the analog measuring circuit
M: Ground terminal of the C7
V
CM
: Potential difference between inputs and M
ANA
V
ISO
: Potential difference between M
ANA
and the M terminal of the
C7
Overview
Cables for Analog
Signals
Isolated Analog
Input
Connecting
Transducers to
Analog Inputs
Abbreviations
C7 Analog Input/Output