Spectrum Controls 1769sc-IF8u - Manual (Page 36)

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.)