Siemens Simatic M7-400 Reference Manual page 291

5.18.2 Measuring Methods and Measuring Ranges of the
SM 431; AI 8
Measuring Methods
You can set the following measuring methods for the input channels:
• Voltage measurement
• Current measurement
• Resistance test
You perform the setting with the "Measuring Type" parameter in STEP 7.
Wiring for Resistance Measurement
The following conditions apply when measuring the resistance with the SM 431;
AI 8 x 13 Bit:
Table 5-49 Channels for Resistance Measurement of the SM 431; AI 8
Measuring Type
Parameter
Resistance
(four-conductor
connection)
Unused Channels
Unused channels can usually be left open. You can improve the noise immunity of
the module in a measuring environment with serious interference by short-circuiting
the channels and connecting to M
unused channels. In this way you shorten the scan time of the module.
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
13 Bit
Permissible
for Channel n
0, 2, 4 or 6 You must disable the( "Measuring Type" parameter for
channels n+1 (1, 3, 5, 7).
The reason: The connections of channel n+1 are used to
supply the resistance that is connected to channel n.
ANA
13 Bit
Condition
. Disable the "Measuring Type" parameter for
Analog Modules
5-75