Siemens SIMATIC Manual page 327

Unused channels
Set the "disabled" value at the "measuring method" parameter for unused channels. This
setting reduces module cycle times.
As certain programmed inputs may remain unused due to the channel group configuration in
8-channel mode, make allowances for the special features of these inputs outlined below to
activate the diagnostics functions at the channels being used:
● Measuring range 1 V to 5 V: wire the used input and unused input of the same channel
group in parallel.
● Current measurement, 4 to 20 mA: Connect unused input in series to the input of the
same channel group. A shunt resistor must be connected for each programmed and
unused channel.
● Other measuring ranges: Short-circuit the plus and minus inputs of the channel.
Line continuity check
The wire break test is available for the voltage measuring range 1 to 5 V and the current
measuring range 4 to 20 mA.
When there is a configured measuring range of 1 to 5 V or 4 to 20 mA and the wire break
test is activated, the analog input module reports a wire break in the diagnostics when
underflow (-32768) is reached.
● The module also triggers a diagnostic interrupt if this function is enabled in the program.
● A wire break can only be signaled by means of the lit SF LED and the diagnostic bytes
must be evaluated in the user program if diagnostic interrupts are disabled.
Under the following circumstances, wire-break detection can take up to 2 s:
● If a wire break occurs during voltage measurement.
● If a wire break occurs on the front-connector jumpers from shunt (250 Ω) to the inputs
during current measurement.
The measured value can go through the entire valid value range during the wire break
detection.
When there are configured measuring ranges ± 10 V, ± 5 V, 1 to 5 V or 4 to 20 mA, the wire
break test is not activated and a diagnostic interrupt is enabled, the module triggers a
diagnostic interrupt when the underflow is reached. The module detect the underflow when
the input signal is below 0.296 V or 1.185 mA.
Overflow, underflow and hardware interrupt limits
The limits in diagnostics response to overflow and underflow in certain measuring ranges
differ compared to the listed ranges starting at the chapter
analog input channels
module software used to evaluate the process variables do not return values up to 32511.
Do not set any hardware interrupt limits higher than the lowest possible overflow or
underflow response limits. End of cycle interrupt starting at the chapter
representation for analog input channels
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
6.4 Analog input module SM 331; AI 8 x 16 Bit; (6ES7331-7NF10-0AB0)
of the manual. In certain situations the numerical methods of the
.
Analog modules
Analog value representation for
Analog value
327