Siemens SIMATIC PCS 7 System Manual page 81

Redundant analog input modules with non-redundant encoder
With non-redundant encoders, analog input modules are used in a 1-out-of-2 configuration:
Figure 4-19
Remember the following when connecting an encoder to multiple analog input modules:
● Connect the analog input modules in parallel for voltage sensors (left in figure).
● You can convert a current into voltage using an external load to be able to use voltage
analog input modules connected in parallel (center in the figure).
● 2-wire transmitters are powered externally to allow you to repair the module online.
The redundancy of the fail-safe analog input modules enhances their availability.
If you do not use terminal modules, see the interconnection examples in the Appendix
Connection examples for redundant I/Os (Page 323).
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 transmitters with voltage output and
thermocouples.
● The "wire break" diagnostics function in HW Config must not be activated, neither when
operating the modules with transmitters nor when thermocouples are connected.
● Suitable encoder types are active 4-wire and passive 2-wire transmitters with output
ranges +/-20 mA, 0...20 mA, and 4...20 mA. 2-wire transmitters are powered by an
external auxiliary voltage.
● Criteria for the selection of resistance and input voltage range are the measurement
accuracy, number format, maximum resolution and possible diagnostics.
● In addition to the options listed, other input resistance and voltage combinations
according to Ohm's law are also possible. Note, however, that such combinations may
lead to loss of the number format, diagnostics function and resolution. The measurement
error also depends largely on the size of the measure resistance of certain modules.
● Use a measure resistance with a tolerance of +/- 0.1% and TC 15 ppm.
CPU 410-5H Process Automation/CPU 410 SMART
System Manual, 09/2014, A5E32631667-AB
4.7 Connecting redundant I/O to the PROFIBUS DP interface
Fault-tolerant analog input modules in 1-out-of-2 configuration with one encoder
I/O configuration variants
81