Siemens SIMATIC S7-400H System Manual page 143

Remember the following when connecting an encoder to multiple analog input modules:
● Connect connect the analog input modules in parallel for voltage encoders (left in
● You can convert a current into voltage using an external load to use voltage analog input
● 2-wire measuring transducers are powered externally to allow you to repair the module
The redundancy of the fail-safe analog input modules enhances their availability.
You will find connection examples in Appendix F.
Redundant analog input modules for indirect current measurement
The following applies to the wiring of analog input modules:
● Suitable encoders for this circuit are active measuring transducers with voltage output
● The "Wire break" diagnostics function in HW Config must not be activated either when
● Suitable encoder types are active 4-wire and passive 2-wire measuring transducers with
● Criteria for the selection of resistance and input voltage range are the measurement
● In addition to the options listed, other input resistance and voltage combinations
● Use a measurement resistance with a tolerance of +/-0.1 % and TC 15 ppm.
S7-400H
System Manual, 09/2007, A5E00267695-03
illustration).
modules connected in parallel (center in the illustration).
online.
and thermocouples.
operating the modules with measuring transducers or when thermocouples are
connected.
output ranges +/-20 mA, 0...20 mA and 4...20 mA. 2-wire measuring transducers are
powered by an external auxiliary voltage.
accuracy, number format, maximum resolution and possible diagnostics.
according to Ohm's law are also possible. Note, however, that such combinations may
lead to the loss of the number format, diagnostics function and resolution. The
measurement error also depends largely on the size of the shunt resistance for certain
modules.
Using I/Os in S7-400H
10.5 Connecting redundant I/Os
143