Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 74)

74 Rockwell Automation Publication 1756-UM533C-EN-P - February 2011
Chapter 5 1756-IF16H HART Analog Input Module
For devices powered by individual supplies, when the ground potential of the
supplies is expected to differ, differential mode is recommended. This prevents
ground loop currents from flowing between the supplies. However, the potential
difference allowable between the supplies must remain within the specified
limits.
Figure 15 - Power Supplies with Isolated Grounds
Some devices ,such as AC powered four wire devices, are recommended to be
used in differential mode only. Combinations of differential and single-ended
configurations are allowed but care must be taken to insure that the differential
input grounds really are isolated from the single-ended inputs.
Circuit Diagram This figure is a simplified input circuit diagram for the 1756-IF16H module.
Figure 16 - 1756-IF16H Simplified Current Input Circuit
Ground wire isolated
from each other.
Power Supply 1
Power Supply 2
The low end of the terminal block pins are now isolated from each other
and the inputs can be configured as true differential inputs as long as the
voltage difference between them does not exceed 7V.
HART Device 1
HART Device 2
+ -
+ -
RTN
45121
23.7 Ω
Analog to
Digital
Converter
22 K
Ω
RTN
IGND
+
-
0.01 μF
113 Ω
10 M Ω INO+
INO- Current
Input
i
45117
22 K Ω
113 Ω
IGND
0.01 μF
10 M Ω
IGND