Siemens Simatic S7-400 - Manual (Page 291)

Analog Modules
5-75
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
5.18.2 Measuring Methods and Measuring Ranges of the
SM 431; AI 8
13 Bit
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 13 Bit
Measuring Type
Parameter
Permissible
for Channel n
Condition
Resistance
(four-conductor
connection) 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.
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
ANA
. Disable the “Measuring Type” parameter for
unused channels. In this way you shorten the scan time of the module.