Analog modules
9.3 SM 336; F-AI 6 x 0/4 ... 20 mA HART
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
239
9.3.4
Applications and wiring schemes
Applications
The following applications are associated with the following wiring schemes:
Wiring schemes
Application
A
B
C
D
E
F
G
H
3: 1oo1 evaluation
X
X
X
X
4: 1oo1 evaluation, transducer not redundant, high availability
X
X
X
X
1oo2 evaluation
X
X
X
X
5:
1oo2 evaluation, transducer via 1-channel
X
X
X
X
6: 1oo2 evaluation, transducer via 1-channel, high-availability,
transducer not redundant
X
X
X
X
7: 2oo3 evaluation, high-availability
X
X
X
X
8: 2oo3 evaluation, high-availability, transducer not redundant
X
X
X
X
9: 2oo3 evaluation with 3 modules
X
X
X
X
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
V_min
):
Power supply, e.g., for SITOP 24 V ±2%
U
V_min
= U
V
– |Tolerance| = 24 V – 2% = 23.5 V
(neglecting the voltage drop at the supply line to the module)
●
Calculate the maximum voltage drop at the signal line (U
line
):
e.g. for copper line 500 m with ∅ = 0.5 mm²; with I
max
= 25 mA
5
/LQH
P
˖
PP
PPP
˖
U
Line
= 35.7 Ω × 25 mA = 0.9 V
●
Calculate the voltage drop at the input resistance (U
Ri
) of the module:
–
With R
i_max
= 175 Ω; with I
max
= 25 mA
U
Ri
= 175 Ω × 25 mA = 4.4 V
–
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
Z_5V6
= U
Z
+ Tolerance = 5.6 V + 5% = 5.9 V
U
Z_6V2
= U
Z
+ Tolerance = 6.2 V + 5% = 6.5 V
