Siemens S7-400 ユーザーズマニュアル

5-43

S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07

You can connect different sensors to the analog input modules depending on the
measuring method; voltage and current sensors, and resistors.

This section contains general information that is generally applicable to all the
connection options for sensors described in the sections that follow.

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, which leads to an interference of the analog
signals. In such a case, you should ground the shield at one end of the cable only.

In the case of the non-isolated analog input modules there is an electrical
connection between the reference point of the measuring circuit M

ANA

 and chassis

ground.

You use non-isolated analog modules if there are few or no potential differences
between the measuring sensors and chassis ground.

With the isolated analog input modules there is no electrical connection between
the reference point of the measuring circuit M

ANA

 and chassis ground.

You use isolated analog input modules if a potential difference U

ISO

 can occur

between the reference point of the measuring circuit M

ANA

 and chassis ground. By

means of an equipotential bonding conductor between the M

ANA

 terminal and

chassis ground, make sure that U

ISO

 does not exceed the permitted value.

Only a limited potential difference U

CM

 (common mode voltage) may occur

amongst the M– measuring lines of the input channels and between the leads and
the reference point of the measuring circuit M

ANA

. In order to prevent the

permissible value from being exceeded, you must take different actions, described
below, depending on the potential connection of the sensors.