Siemens Simatic S7-300 - Additional Information to SM 331; AI 8 X 12 Bit

Analog modules
6.7 Analog input module SM 331; AI 8 x 12 Bit;(6ES7331-7KF02-0AB0)
S7-300 Automation System Module data
6-60 Manual, 08/2006, A5E00105505-04
6.7.3 Additional information to SM 331; AI 8 x 12 Bit
Unused channels
Certain inputs of the channel group configuration may remain unused. To enable diagnostic
functions at the used channels, note the special features of those inputs outlined below:
● Current measurement (other than 1 to 5V) and for thermocouples: You must short-circuit
unused channels and connect them to M
ANA
. This optimizes interference immunity of the
analog input module. For unused channels, set the "disabled" instruction at the
"measuring method" parameter. This reduces the module's cycle time. If not used, short-
circuit the COMP input.
● Measuring range 1 V to 5 V: wire the used and unused inputs of the same channel group
in parallel.
● Current measurement, 2-wire transducer: There are two options of wiring the channel
circuit.
a) Open unused input; channel group diagnostics disabled. If you were to enable
diagnostics, the analog module would trigger a single diagnostic interrupt, and light up its
SF LED.
b) Loading the unused input using a 1.5 kΩ to 3.3 kΩ resistor. This allows you to enable
diagnostics for this channel group.
● Current measurement 4 mA to 20 mA, 4-wire transducer: wire the unused inputs of the
same channel group in series.
All channels deactivated
If you disable all input channels of the module and enable diagnostics you configure the SM
331; AI 8 x 12 Bit analog input modul, the module does not indicate "external auxiliary
voltage missing."
Wire-break check function in the 4 mA to 20 mA measuring range
If you configured a measuring range of 4 mA to 20 mA, and enabled wire-break check, the
analog input module logs a wire-break event in diagnostics data when the current drops
below 3.6 mA.
The module also triggers a diagnostic interrupt if you enabled diagnostics interrupts in the
program.
The lit SF LED is otherwise the only indication of the wire-break, and you must evaluate the
diagnostic bytes in the user program.
If you configured a measuring range of 4 mA to 20 mA, disabled wire-break check, and
enabled diagnostic interrupts, the module triggers a diagnostic interrupt when the underflow
value is reached.
Wirebreak monitoring
The wire-break check function is designed only for temperature measurements
(thermocouples and thermoresistors.)
See also
Representation of the analog values of analog input channels (Page 5-2)