Analog Modules
4-94
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Scan time of the module
In 4-channel mode, the channel conversion time including communication time of
the SM 331; AI 8 x 16 bits is 10 ms. As the module does not switch over between
the channels in a group, the channel scan time and the module
scan time are the same: 10 ms.
4.19.4 Measuring Methods and Measuring Ranges of the SM 331;
AI 8 x16 bits
Measuring Methods
You can set the following measuring methods for the input channels:
• Voltage measurement
• Current measurement (4-wire transmitter)
You perform the setting with the “measuring method” parameter in STEP 7.
Unused Channels
Set the “measuring method” parameter for unused channels to “disabled”. In this
way you shorten the scan time of the module.
Since configured inputs can remain unused because of the channel group
generation, you must take note of the following special characteristics of these
inputs to enable the diagnostic functions on the used channels.
• Measuring range 1 to 5 V: Connect the unused input in parallel with a used
input of the same channel group.
• Current measurement, 4 to 20 mA: Connect the unused input in series with
an input of the same channel group. Ensure that a current sense resistor is
connected for each active and unused channel.
• Other ranges: Short the positive to the negative input of the channel.
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