Siemens SIMATIC ET 200S, Руководство пользователя

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Analog Electronic Modules
12-17
ET 200S Distributed I/O System
EWA-4NEB 780602402-12
12.2 Basics of Analog Value Processing
12.2.1 Connecting sensors
Introduction
Depending on the module various sensors can be connected to the analog input
modules:
•
Voltage sensor
•
Current sensor as
-- 2-wire measuring transducer
-- 4-wire measuring transducer
•
Resistance
This chapter describes how to connect the sensors and what you must consider
when connecting the sensors.
Cables for analog signals
Shielded and twisted-pair cables must be used for the analog signals. This reduces
influences from interference. The shield for the analog cables must be grounded at
both ends of the cable. If there are potential differences between the ends of the
cable, an equipotential bonding current flows through the shield, which may
interfere with the analog signals. In this case the shield should be grounded at one
end only.
Analog input modules
The analog input modules are isolated:
•
Between logic and backplane bus
•
Between load voltage and the channels. There are the following differences:
-- (no galvanic isolation). connection between M
ANA
and the central ground
point
-- Electrical isolation: no connection between M
ANA
and the central ground
point (U
ISO
)