Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 138)

138 Rockwell Automation Publication 1769-UM004B-EN-P - March 2010
Appendix D Using Thermocouple Junctions
As shown in the next illustration, using an exposed junction thermocouple can
result in removal of channel-to-channel isolation. Isolation is removed if multiple
exposed thermocouples are in direct contact with electrically conductive process
material.
Figure 54 - Exposed Junction Thermocouple Results in Removal of
Channel-to-channel Isolation
Follow these guidelines to prevent violation of channel-to-channel isolation.
• For multiple exposed junction thermocouples, do not allow the measuring
junctions to make direct contact with electrically conductive process
material.
• Preferably use a single exposed junction thermocouple with multiple
ungrounded junction thermocouples.
• Consider using all ungrounded junction thermocouples instead of the
exposed junction type.
+
-
IN 0
+
-
IN 3
1769-IT6
Exposed Junction with Shielded Cable
Multiplexer Conductive Material