CiDRA SONARtrac HD VF-100 - Manual (Page 57)

Copyright © 2006 CiDRA Corporation Page 9-5
20638-02 Rev 01
Externally Powered 4-20mA Loop Configuration - The hookup for a
4-20mA interface configured as “Externally Powered” is shown below.
The maximum value of V
EXT
should be chosen such that the maximum
applied voltage between V
EXT
and local ground and I
OUT
and local
ground shall be within the range of +30V / -10V and current limited to
100mA. The maximum value of R
L
is determined by the following
equation:
R
L Max
= (V
EXT
– 8.35) / (0.022)
For example, with V
EXT
= 24VDC:
R
L Max
= (24-8.35) / (0.022) = 711 Ohms
In the externally powered configuration the 4-20mA interface is
capacitively isolated from the rest of the transmitter electronics
provided that the applied voltages are within +30V / -30V.
Figure 50 Externally Powered 4–20mA Loop
SHD - The three SHD (shield) terminals should only be used for
grounding shields of any output wiring such as connections to CUR 1
or CUR2. These should not be used for the SENSOR 1 or 2 shields
or for the Sensor Head To Transmitter cable shield. Only one end of
the shield wire should be connected to eliminate shield currents.
Plant Control System
R
L
+
-
V
EXT
SONARtrac TM Transmitter
4-20mA
Driver