Analog modules
6.9 Analog input module SM 331; AI 8 x RTD; (6ES7331-7PF01-0AB0)
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
6-85
Cycle time extension due to wire-break monitoring
The wire-break monitoring software function of the module is available in all operating
modes.
The cycle time of the module is doubled in 8-channel mode (hardware or software filter),
irrespective of the number of channels at which wire-break monitoring is enabled.
In 4-channel mode (hardware filter), the module interrupts processing of input data for the
duration of 100 ms to perform a wire-break check, i.e. each wire-break check extends the
module cycle time by 100 ms.
Unused channels
In order to avoid incorrect measurements, the module's product version 02 must be
configured with an unused channel of an active group of channels. To suppress a diagnosis
error in the unused channel, the configuration should include a resistor of the nominal range.
For unused channels, set the "disabled" instruction at the "measuring method" parameter.
This reduces the module's cycle time.
Short-circuit to M or L
If you short-circuit an input channel to M or L, the module does not suffer any damage. The
channel continues to output valid data and does not report a diagnostics event.
End of cycle interrupt
You can synchronize a process with the conversion cycle of the module by enabling the end
of cycle interrupt. The interrupt occurs when the conversion of all the enabled channels is
complete.
The following table shows the content of the 4 bytes of additional OB40 information during
hardware or end of cycle interrupts.
Content of the 4 bytes of additional information 2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Byte
2 bits per channel to identify the range
High limit exceeded at channel 7 6 5 4 3 2 1 0 0
Low limit exceeded at channel 7 6 5 4 3 2 1 0 1
End of cycle event X 2
Special
analog flags
Free bit 3
Programming restrictions when operating SM 331; AI 8 x RTD with PROFIBUS masters which only
support DPV0.
When operating the SM 331; AI 8 x RTD analog input module on an ET 200M PROFIBUS
slave system and the PROFIBUS master is not an S7 master, certain parameters are not
permitted. Non-S7 masters do not support hardware interrupts. All parameters associated
with those functions are thus disabled. This includes hardware interrupt enable, hardware
restrictions and end of cycle interrupt enable. All other parameters are permitted.
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