User Manual

Publication 1790-UM001A-EN-P - March 2002
2-8 Installation and Wiring
I/O System
Wiring Guidelines
Consider the following when wiring your system:
General
• All module commons (COM) are connected in the analog
module. The analog common (COM) is not connected to earth
ground inside the module.
• Channels are not isolated from each other.
• Do not use the analog module’s NC terminals as connection
points.
• To ensure optimum accuracy, limit overall cable impedance by
keeping your cable as short as possible. Locate the I/O system
as close to your sensors or actuators as your application will
permit.
• Use Belden™ 8761, or equivalent, shielded wire.
• Keep shield connection to ground as short as possible.
• Under normal conditions, the drain wire and shield junction
must be connected to earth ground via a panel or DIN rail
mounting screw at the analog I/O module end.
(1)
Input Modules
• If multiple power supplies are used with analog inputs, the
power supply commons must be connected together.
• The module does not provide loop power for analog inputs. Use
a power supply that matches the input transmitter specifications.
Output Modules
• Voltage outputs (CH0 and CH1) of the 1790D-NOV2/TNOV2
modules are referenced to COM. Load resistance for a voltage
output channel must be equal to or greater than 1K
Ω.
• Current outputs (CH0 and CH1) of the 1790D-NOC2/TNOC2
modules source current that returns to COM. Load resistance for
a current output channel must remain between 0 and 600
Ω.
(1)
In environments where high-frequency noise may be present, it may be necessary to directly ground cable
shields to earth at the module end and via a 0.1µF capacitor at the sensor end.