II - DCE FEL ČVUT v Praze

Abbreviations
Insulated
measured value
sensors
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04
The abbreviations used in Figs. 3-1 and 3-2 have following meanings:
M +: Measuring conductor (positive)
M -: Measuring conductor (negative)
UISO: Differences in potential between inputs and ground terminal M
UCM: Differences in potential between inputs
L+: Power supply connection 24 V DC
M: Ground terminal for 24 V DC power supply
P5V: Supply voltage of module logic
Minternal: Ground of module logic
Insulated measured value sensors are not connected to the local ground
potential. They facilitate floating operation. Due to local conditions or
interference, differences in potential UCM (static or dynamic) can occur
between the input channels. However, these differences in potential must not
exceed the permissible values for UCM. If there is a possibility that the
permissible value may be exceeded, the M- terminals of the input channels
must be interconnected.
If there is a possibility of exceeding the permissible value for UISO (inputs
with respect to backplane bus), the M- terminals of the input channels must
be connected to the M- terminal of the CPU.
Fig. 3-1 shows the connection principle of insulated transducers to an
isolated analog input module.
Insulated
transducers
U CM
U ISO
U ISO
M+
M-
M+
M-
ADU
SIMATIC S7 Ex Analog Modules
Ground bus
P5V
M internal
Logic
CPU
Backplane
bus
Fig. 3-1 Connection of insulated transducers to an isolated analog input module
M
L+
M
3-23