Allen-Bradley MicroLogix 1200, User Manual, Page: 24 / 144

Publication 1762-UM002A-EN-P - July 2002
2-8 Installation and Wiring
Terminal Block
•
Do not tamper with or remove the CJC sensor on the terminal
block. Removal of the sensor reduces accuracy.
•
For millivolt sensors, use Belden 8761 shielded, twisted-pair
wire (or equivalent) to ensure proper operation and high
immunity to electrical noise.
•
For a thermocouple, use the shielded, twisted-pair
thermocouple extension lead wires specified by the
thermocouple manufacturer. 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
•
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.
•
Under normal conditions, the drain wire (shield) should be
connected to the metal mounting panel (earth ground). Keep
shield connection to earth 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.
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.