Siemens SIMATIC S7-400H System Manual page 136

Using I/Os in S7-400H
10.5 Connecting redundant I/Os
Module
Central: Redundant AI dual-channel
AI 6x16-bit
Use in voltage measurement
•
Use in indirect current measurement
•
Use in direct current measurement
•
•
•
Note: The circuit shown in Figure 8-10 works only with active (4-wire) measuring transducers, or with
passive (2-wire) measuring transducers with external power supply. Always configure the module
channels for operation as "4-wire measuring transducer", and set the measuring range cube to
position "C".
It is not possible to power the measuring transducers via the module (2DMU).
Distributed: Redundant AI dual-channel
AI8x12-bit
Use for indirect current measurement
•
•
•
•
Use of redundant encoders:
•
136
The "Wire break" diagnostics function in HW Config must not be activated either when operating
the modules with measuring transducers or when thermocouples are connected.
Use a 250 ohm resistor to convert the current to a voltage; see page 8–32.
Suitable Zener diode BZX85C6v2 or 1N4734A (6.2 V because of the 50 ohm input resistance)
Load capability of 4-wire measuring transducers: R
(worst-case: 1 input + 1 Zener diode at an S7 overshoot value 24 mA to R
Input voltage for 2-wire measuring transducers: U
(worst-case: 1 input + 1 Zener diode at an S7 overshoot value 24 mA to U
The total input resistance in measuring ranges > 2.5 V can be reduced from a nominal 100 kilohms
to 50 kilohms when operating two inputs in parallel.
The "Wire break" diagnostics function in HW Config must not be activated either when operating
the modules with measuring transducers or when thermocouples are connected.
Use a 50 ohm or 250 ohm resistance to convert the current to a voltage; see page 8–31.
This module is not suitable for direct current measurement.
You can use a redundant encoder with the following voltage settings:
+/- 80 mV (only without wire break monitoring)
+/- 250 mV (only without wire break monitoring)
+/- 500 mV (wire break monitoring not configurable)
+/- 1 V (wire break monitoring not configurable)
+/- 2.5 V (wire break monitoring not configurable)
+/- 5 V (wire break monitoring not configurable)
+/- 10 V (wire break monitoring not configurable
1...5 V (wire break monitoring not configurable)
Order number
6ES7431–7QH00–0AB0
> 325 ohms
B
= (R
B
< 8 V
e-2w
e-2w
6ES7331–7KF02–0AB0
System Manual, 09/2007, A5E00267695-03
* I + U ) / I )
E max z max max
= R * I + U )
E max z max
S7-400H