Siemens SIMATIC S7-300 Reference Manual page 360

Analog Modules
Terminal Connection Diagram and Block Diagram of the
Fault indicator – red
SF
Figure 4-49 Module View and Block Diagram of the Analog Input Module SM 331; AI 2 x 12 bits
The input resistances depend on the measuring range selected (refer to the
technical specifications for the module).
4-154
Thermocouples,
Voltage measurement
Current measurement
Current
Internal
Multi-
source
supply
plexer
Internal
T
compensation
External
+
compensation
None
ADC
Isolation
SF
Backplane
bus
interface
SM 331; AI 2 x 12 bits
L+
24V
M
Meas. range
module
M
M
M
Comp
M
Programmable Logic Controllers S7-300 Module Data
Resistance test
M
0 + CH0
0 + CH0
M
0*
0*
I
1 + CH1 C0 +
I
C0*
1*
Comp +
Comp–/ Mana
A5E00105505-03