II - DCE FEL ČVUT v Praze

SIMATIC S7 Ex Analog Modules
3.4 Connecting Current Sensors and Transducers to the Analog Input
Module SM 331; AI 4 x 0/4...20 mA
Abbreviations
Connection of
current sensors as
2-wire and 4-wire
transducers
3-34
The following description refers to the operation of transducers together with
the analog input module SM 331; AI 4 x 0/4...20 mA.
The abbreviations used in Figs. 3-11 to 3-12 have the following significance:
L0+ ... L3+ : Isolated transducer supply per channel
M+ : Measuring line (positive)
M- : Measuring line (negative)
L+ : Power supply connection 24 V DC
M : Ground terminal for 24 V DC power supply
UM: Measuring-circuit voltage
RS: Measuring shunt
UV+, UV-: External transducer supply voltage
The 2-wire transducer is supplied short-circuit-proof via the isolated
measuring transducer supply L0+ ... L3+ of the corresponding analog channel.
The 2-wire transducer then converts the supplied measured variable into a
current between 4...20 mA.
4-wire transducers feature a separate supply voltage connection which must
be powered by an external power supply unit.
The information provided in Section 3.2 on differences in potential UCM and
UISO between the individual circuits still retains its validity.
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04