Redundant Analog Input Modules For Indirect Current Measurement - Siemens SIMATIC S7-400H Manual

Redundant analog input modules for indirect current measurement

To note when wiring analog input modules as shown in the diagram above:
• Suitable for use in the circuit shown above are active measurement transducers
with voltage output and thermocouples
• The "wire break" diagnostic function may not be enabled in HW Config when
the module is operated with measurement transducers or thermocouples
• Suitable sensor types are active 4-wire and passive 2-wire-measuring
transducers with output ranges +/–20mA, 0...20mA and 4...20mA.
2-wire-measuring transducers are supplied via an external auxiliary voltage.
• The resistance and input voltage range is selected according to the
measurement precision, number format, maximum resolution and possible
diagnostics criteria.
• Other input resistance and voltage combinations according to ohms law are
also possible in addition to the options listed. However, note that the number
format, diagnostic options and resolutions will be lost. Likewise is the
measurement error highly dependent on the amount of the shunt resistance for
certain modules.
• Use a measurement resistance of type tolerance +/– 0,1% and TK 15ppm.
Module not suitable for use in the circuit shown above:
AI 4x15bit Ex
Additional marginal conditions for various modules
AI 8x12bit
AI 8x12bit
• The modules have a low common mode voltage of 2.5 V. Careful layout of the
wiring circuit is therefore vital, particularly when using encoders referenced to
ground (encoders with floating potential do not have this high demand on wiring
quality).
• The rated accumulated input resistance is reduced from > 150 Ohm to 50 Ohm
when two inputs with the measuring range > 2.5 V are wired in parallel.
Depending on accuracy requirements, it is useful to calculate accuracy based
on the source and line resistance.
• The "wire break" diagnostic function may not be enabled in HW Config when
the module is operated with measurement transducers or thermocouples
• You can use a 50 Ohm or 250 Ohm shunt resistor for voltage measurements:
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
6ES7 331-7RD00-0AB0 I-Input
6ES7 331-7K..01-0AB0
6ES7 331-7K..02-0AB0
Using I/O on the S7-400H
7-25