Siemens SIMATIC S7-400H System Manual page 200

Using I/Os in S7–400H
13.4 Connecting redundant I/O to the PROFIBUS DP interface
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
● The "wire break" diagnostics function in HW Config must not be activated, neither when
● Suitable encoder types are active 4-wire and passive 2-wire transmitters with output
● 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 measure resistance with a tolerance of +/- 0.1% and TC 15 ppm.
Additional conditions for specific modules
AI 8x12bit 6ES7 331–7K..02–0AB0
● Use a 50 ohm or 250 ohm resistor to map the current on a voltage:
Resistor
Current measuring range
Input range to be parameterized
Measuring range cube position
Resolution
S7 number format
Circuit-specific measuring error
- 2 parallel inputs
- 1 input
"Wire break" diagnostics
Load for 4-wire transmitters
Input voltage for 2-wire transmitters
*) The AI 8x12bit outputs diagnostic interrupt and measured value "7FFF" in the event of wire break.
The listed measuring error results solely from the interconnection of one or two voltage
inputs with a measure resistance. Allowance has neither been made here for the tolerance
nor for the basic/operational limits of the modules.
200
thermocouples.
operating the modules with transmitters nor when thermocouples are connected.
ranges +/-20 mA, 0...20 mA, and 4...20 mA. 2-wire transmitters 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 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.
50 ohms 250 ohms
+/-20 mA +/-20 mA *)
+/-1 V +/-5 V
"A" "B"
12 bits + sign 12 bits + sign
x x
- 0.5%
- 0.25%
- -
50 ohms 250 ohms
> 1.2 V > 6 V
System Manual, 03/2012, A5E00267695-11
4...20 mA
1...5 V
12 bits
x *)
S7-400H