Kobold NRM, Operating Manual

Page: 11 / 52

NRM
NRM K06/0422 page 11
Power
supply
Power supply
+HART
+Current output
HART modem
I
brown
white
green
green/
yellow
R
yellow
TR
A
N
SM
ITT
ER
mA
V
200mV
Extension of the integrated cable:
The usage of a junction box is recommended for extending the cable.
The shielding of the two cables should be connected and grounded at the signal
processing device.
7.2 Determine the appropriate power supply voltage
The minimal power supply voltage required by the NRM devices is depending on
the load impedance in accordance to the below diagram:
22
21
20
19
18
17
16
15
14
13
12
2 4
6 8 10
12 14
16 18 20
22
19,1
13,6
B
A Minimal supply voltage
on the input terminals
of the device
Minimal supply voltage
(considering the voltage drop
on the 250 Ohm loop resistor)
A : minimal supply voltage on the input
terminals of the device
B: minimal supply voltage (considering the
voltage drop on the 250 Ohm loop resistor)
Calculation example: Voltage drop calculated with 22 mA:
U
minimal supply voltage (22 mA)
= 22 mA x load res U
input minimum (22 mA)
U
minimal supply voltage (22 mA)
= 22 mA x 250 Ohm + 9 V = 5.5 V + 13.6 V = 19.1 V
In order to provide operation in the total current loop range the calculation should
be also checked with 4 mA: