Applications And Wiring Schemes; Calculation Of The Residual Supply Voltage At The Transducer - Siemens S7-300 Installation And Operating Manual

9.3.4

Applications and wiring schemes

Applications
The following applications are associated with the following wiring schemes:
3: 1oo1 evaluation
4: 1oo1 evaluation, transducer not redundant, high availability
5: 1oo2 evaluation
1oo2 evaluation, transducer via 1-channel
6: 1oo2 evaluation, transducer via 1-channel, high-availability,
transducer not redundant
7: 2oo3 evaluation, high-availability
8: 2oo3 evaluation, high-availability, transducer not redundant
9: 2oo3 evaluation with 3 modules
9.3.4.1

Calculation of the residual supply voltage at the transducer

Calculation of residual supply voltage
Determine the following voltages, according to your wiring scheme, for the purpose of
calculating the residual supply voltage:
● Determine the minimum supply voltage (U
● Calculate the maximum voltage drop at the signal line (U
● Calculate the voltage drop at the input resistance (U
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
Application
Power supply, e.g., for SITOP 24 V ±2%
U = U – |Tolerance| = 24 V – 2% = 23.5 V
V_min V
(neglecting the voltage drop at the supply line to the module)
e.g. for copper line 500 m with ∅ = 0.5 mm²; with I
U = 35.7 Ω × 25 mA = 0.9 V
Line
– With R = 175 Ω; with I
i_max
U = 175 Ω × 25 mA = 4.4 V
Ri
– When Zener diodes are used in a high-availability application, this higher voltage shall
be used, taking into account the tolerances.
e.g., when using Zener diodes with 5.6 V and 6.2 V:
U = U + Tolerance = 5.6 V + 5% = 5.9 V
Z_5V6 Z
U = U + Tolerance = 6.2 V + 5% = 6.5 V
Z_6V2 Z
9.3 SM 336; F-AI 6 x 0/4 ... 20 mA HART
A B
X X
X X
X X
X X
X X
):
V_min
max
= 25 mA
max
Analog modules
Wiring schemes
C D E F
X X
X X
X X
X X
X X
X X
X X
X X
):
line
= 25 mA
) of the module:
Ri
G H
X X
X X
X X
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