Siemens SIMATIC S7-400H System Manual page 145

● Use a 50 ohm or 250 ohm resistance to convert the current to a voltage:
Resistance
Current measuring range
Input rangeto be configured
Measuring range cube position
Resolution
S7 number format
Circuit-specific Measuring error 1)
- 2 parallel inputs
- 1 input
"Wire break" diagnostics
Load for 4-wire measuring transducers
Input voltage for 2-wire measuring
transducers
Redundant analog input modules for direct current measurement
Requirements for wiring analog input modules according to Figure 8-10:
● Suitable encoder types are active 4-wire and passive 2-wire measuring transducers with
● The "wire break" diagnostics function supports only the 4...20 mA input range. All other
● Suitable diodes include the BZX85 or 1N47..A series (Zener diodes 1.3 W) with the
● A fundamental measuring error results from this type of circuit and the specified diodes,
● The 4-wire measuring transducers used must be capable of driving the load resistance
● When connecting up 2-wire measuring transducers, note that the Zener diode circuit
S7-400H
System Manual, 09/2007, A5E00267695-03
output ranges +/-20 mA, 0...20 mA and 4...20 mA. 2-wire measuring transducers are
powered by an external auxiliary voltage.
unipolar or bipolar ranges are excluded in this case.
voltages specified for the modules. When selecting other elements, make sure that the
reverse current is as low as possible.
due to the maximum reverse current of 1 µA. In the 20 mA range, and at a resolution of
16 bits, this leads to an error of < 2 bits. Individual analog inputs in the circuit above lead
to an additional error, which may be listed in the constraints. The errors specified in the
manual must be added to these errors for all modules.
resulting from the circuit above. You will find details in the technical specifications of the
individual modules.
weighs heavily in the power budget of the measuring transducer. The required input
voltages are therefore included in the technical specifications of the individual modules.
Together with the inherent supply specified on the measuring transducer data sheet, the
minimum supply voltage is calculated to L+ > U
10.5 Connecting redundant I/Os
50 ohms 250 ohms
+/-20 mA +/-20 mA
+/-1 V +/-5 V
"A" "A"
15-bit + sign 15-bit+sign
x x
- -
- -
- -
50 ohms 250 ohms
> 1.2 V > 6 V
+ U
e-2w EV-MU
Using I/Os in S7-400H
4...20 mA
1...5 V
15-bit
x
145