Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 94)

94 Publication 1756-UM009C-EN-P - December 2010
Chapter 5 Sourcing Current Loop Input Module (1756-IF6CIS) and Isolated Analog Voltage/Current Input Module (1756-IF6I)
Use the Isolated Power
Source on the 1756-IF6CIS The 1756-IF6CIS module offers an internal power source on each channel.
The source is current limited to 28 mA and allows the module to power a
two-wire transmitter directly without the need for an external power supply.
The transmitter can then vary the current to the analog input in proportion to
the process variable being measured. The inclusion of an internal on-board
current source saves you the expense of extra power supplies and greatly
simplifies the interface wiring to field devices.
In addition to supplying loop power to two-wire transmitters, the module can
also accommodate current loops powered by an external supply and loops
using four-wire transmitters.
Power Calculations with the 1756-IF6CIS Module
The 1756-IF6CIS module uses the system power supply (1756-Px7x) as the
source for loop power. Because of the demands placed on that supply (that is,
the 1756-IF6CIS module consumes 7.9 W of backplane power), special care
must be taken when calculating the power requirements for modules in the
same chassis as a 1756-IF6CIS module.
For example, when used with the 1756-L55M13 controller, you can place only
eight 1756-IF6CIS modules in the chassis before exceeding the wattage
capacity of the power supply.
Other Devices in the Wiring Loop
The voltage source on each channel can drive loop impedance of up to
1000 ohms. This lets you include other devices, such as chart recorders and
meters, in the current loop.
For more information on wiring the 1756-IF6CIS module, see page 106 .