User Manual

26 Compact IO
Universal Input module
Using the incorrect type of thermocouple extension wire or not
following the correct polarity will cause invalid readings.
To ensures optimum accuracy, limit overall cable impedance by
keeping a cable as short as possible. Locate the module as close to
input devices as the application permits.
Grounding
!
ATTENTION! The possibility exists that a grounded or exposed
thermocouple can become shorted to a potential greater than that of the
thermocouple itself. Due to possible shock hazard, take care when wiring grounded
or exposed thermocouples. See Appendix D, Using Thermocouple Junctions.
· This product is intended to be mounted to a well-grounded mounting
surface such as a metal panel. Additional grounding connections
from the module’s mounting tabs or DIN rail (if used) are not
required unless the mounting surface cannot be grounded.
· Keep cable shield connections to ground as short as possible.
· Ground the shield drain wire at one end only. The typical location is
as follows.
For grounded thermocouples or millivolt sensors, this is at the
sensor end.
For insulated/ungrounded thermocouples, this is at the module end.
Contact your sensor manufacturer for additional details.
· If it is necessary to connect the shield drain wire at the module end,
connect it to earth ground using a panel or DIN rail mounting screw.
· Refer to Industrial Automation Wiring and Grounding Guidelines,
Allen-Bradley publication 1770-4.1, for additional information.
Noise Prevention
· To limit the pickup of electrical noise, keep thermocouple and
millivolt signal wires as far as possible from power and load lines.
· If noise persists for a device, try grounding the opposite end of the
cable shield. (You can only ground one end at a time.)