Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 137)

Rockwell Automation Publication 1769-UM004B-EN-P - March 2010 137
Using Thermocouple Junctions Appendix D
Using an Ungrounded
(isolated) Junction
Thermocouple An ungrounded (isolated) junction thermocouple uses a measuring junction that
is electrically isolated from the protective metal sheath. This junction type is
often used in situations when noise will affect readings, as well as situations using
frequent or rapid temperature cycling. For this type of thermocouple junction,
the response time is longer than for the grounded junction.
Figure 52 - Ungrounded (isolated) Junction Thermocouple
Using an Exposed Junction
Thermocouple An exposed junction thermocouple uses a measuring junction that does not have
a protective metal sheath. A thermocouple with this junction type provides the
fastest response time but leaves thermocouple wires unprotected against corrosive
or mechanical damage.
Figure 53 - Exposed Junction Thermocouple
Measuring Junction Isolated from Sheath
Measuring Junction with No Sheath