Analog modules
9.3 SM 336; F-AI 6 x 0/4 ... 20 mA HART
Fail-safe signal modules
240
Installation and Operating Manual, 01/2010, A5E00085586-10
●
Determine the voltage drop at the sensor supply:
U
SensorSupply
= 0.5 V
●
Determine the voltage drop (U
Diode
) at the longitudinal diode for disconnection of the
sensor supply:
e.g., for BYV27-100
–
For 2-wire transducer, with I
max
= 25 mA
U
Diode
= approx. 0.7 V
–
For 4-wire transducer, with I
max
= 300 mA
U
Diode
= approx. 0.9 V
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
min
) on a 2-wire transducer, non-high-availability application:
U
min
= U
V_min
– U
line
– U
Ri
– U
SensorSupply
U
min
= 23.5 V – 0.9 V – 4.4 V – 0.5 V = 17.7 V
Example for calculating the residual supply voltage in application 4:
●
Minimum residual voltage (U
min
) on a 2-wire transducer, high-availability application:
U
min
= U
V_min
– U
Line
– U
Diode
– U
Z_6V2
– U
Ri
– U
SensorSupply
U
min
= 23.5 V – 0.9 V – 0.7 V – 6.5 V – 4.4 V – 0.5 V = 10.5 V
●
Maximum voltage drop (U
Line
) on the supply line of a 4-wire transducer:
e.g. for copper line 500 m with ∅ = 1.5 mm²; with I
max
= 300 mA
5
/LQH
P
˖
PP
PPP
˖
U
Line
= 11.9 Ω × 300 mA = 3.6 V
Minimum supply voltage (U
min
) on a 4-wire transducer, high-availability application:
U
min
= U
V_min
– U
line
– U
Diode
– U
SensorSupply
U
min
= 23.5 V – 3.6 V – 0.9 V – 0.5 V = 18.5 V
Determination of maximum load voltage
U
LoadSensor
> U
LoadModule
Load voltage for sensor
U
LoadSensor
= I
max
× R
Load
