Rockwell Automation 1771-IFF/A INSTL.INSTR FAST ANALOG INPUT - Manual (Page 10)

Publication 1771-IN046B-EN-P - December 2003
10 Fast Analog Input Module
Input connections for the 1771-IFF with:
• single-ended inputs are shown on page 11.
• differential inputs are shown on page 12.
Minimizing Ground Loops
To minimize ground loop current on input circuits:
• use single-ended mode whenever possible
• use 2-wire transmitters with a common power supply
• separate 2-wire and 4-wire transmitters between different modules
• tie 4-wire transmitter and/or separate power supply grounds together
Cable Lengths
Recommended maximum cable length for voltage-mode input devices is 50
feet (15.24m), due to possible signal degradation and electrical noise immunity
in typical industrial environments. Cable length for current-mode input devices
need not be as restrictive because analog signals from these devices are less
sensistive to electrical noise interference.
WARNING
If you connect or disconnect the wiring with field-side
power applied, an electrical arc can occur. This could cause
an explosion in hazardous location installations.
Be sure that power is removed or the area is nonhazardous
before proceeding.
IMPORTANT
Mixing 2-wire and 4-wire transmitter inputs on the same
module is not recommended. Power supply placement can
make it impossible to eliminate ground loops.