Siemens S7-300 Installation And Operating Manual page 240

Analog modules
9.3 SM 336; F-AI 6 x 0/4 ... 20 mA HART
● Determine the voltage drop at the sensor supply:
● Determine the voltage drop (U
Subtract the voltage drop for the line at the internal resistance and at the diodes from the
minimum supply voltage. Proceed according to the wiring scheme for your sensor.
Example for calculating the residual supply voltage in application 3:
Minimum residual voltage (U
U
min
U
min
Example for calculating the residual supply voltage in application 4:
● Minimum residual voltage (U
● Maximum voltage drop (U
Determination of maximum load voltage
U
LoadSensor
Load voltage for sensor
U
LoadSensor
240
U = 0.5 V
SensorSupply
sensor supply:
e.g., for BYV27-100
– For 2-wire transducer, with I
U = approx. 0.7 V
Diode
– For 4-wire transducer, with I
U = approx. 0.9 V
Diode
= U – U – U – U
V_min line Ri
= 23.5 V – 0.9 V – 4.4 V – 0.5 V = 17.7 V
U = U – U – U
min V_min Line
U = 23.5 V – 0.9 V – 0.7 V – 6.5 V – 4.4 V – 0.5 V = 10.5 V
min
e.g. for copper line 500 m with ∅ = 1.5 mm²; with I
U = 11.9 Ω × 300 mA = 3.6 V
Line
Minimum supply voltage (U
U = U – U – U
min V_min line
U = 23.5 V – 3.6 V – 0.9 V – 0.5 V = 18.5 V
min
> U
LoadModule
= I × R
max Load
) at the longitudinal diode for disconnection of the
Diode
= 25 mA
max
= 300 mA
max
) on a 2-wire transducer, non-high-availability application:
min
SensorSupply
) on a 2-wire transducer, high-availability application:
min
– U – U – U
Diode Z_6V2 Ri SensorSupply
) on the supply line of a 4-wire transducer:
Line
) on a 4-wire transducer, high-availability application:
min
– U
Diode SensorSupply
Installation and Operating Manual, 01/2010, A5E00085586-10
= 300 mA
max
Fail-safe signal modules