II - DCE FEL ČVUT v Praze

SIMATIC S7 Ex Analog Modules
3.5 Connecting Loads/Actuators to the Analog Output Module
SM 332; AO 4 x 0/4...20 mA
Introduction
Lines for analog
signals
Isolated analog
output modules
Abbreviations
3-36
The analog output modules can be used to supply loads/actuators with
current.
Shielded lines twisted in pairs are used for analog signals . So as to reduce
interference influence .
You should ground the shield of the analog lines at both ends. If there are
differences in the potential between the line ends , an equipotential bonding
current can flow across the shield and cause interference in the analog signals.
In this case, the shield should only be grounded at one end of the line.
There is no metallic connection between each of the reference points M0- ...
M3- of the analog circuits and the M terminal of the CPU in the isolated
analog output modules.
Isolated analog output modules are used when a difference in potential UISO
can occur between the reference point of the analog circuit M0- ... M3- and the
M-terminal of the CPU. Take particular care to ensure that the difference in
potential UISO does not exceed the permissible value. In cases where it is
possible that the permissible value is exceeded, provide a connection
between the terminals M0- ... M3- and the M-terminal of the CPU.
The abbreviations used in Fig. 3-13 have the following significance:
QI0- ... QI3-: Analog outputs current
M0- ... M3-: Reference potential of analog output circuit
RL: Load/actuator
L+: Power supply connection 24 V DC
M : Ground terminal for 24 V DC power supply
UISO: Difference in potential between reference points of channels
M0- ... M3- or between the channels and M- terminal of the
CPU.
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04