Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 135)

Rockwell Automation Publication 1769-UM004B-EN-P - March 2010 135
Appendix
D
Using Thermocouple Junctions
This appendix describes the types of thermocouple junctions available, and
explains the trade-offs in using them with the 1769-IT6 thermocouple/mV
analog input module.
Available thermocouple junctions are:
• grounded.
• ungrounded (isolated).
• exposed.
Using a Grounded Junction
Thermocouple With a grounded junction thermocouple, the measuring junction is physically
connected to the protective sheath, forming a completely sealed integral junction.
If the sheath is metal (or electrically conductive), there is electrical continuity
between the junction and sheath. The junction is protected from corrosive or
erosive conditions. The response time approaches that of the exposed junction
type described in
Using an Exposed Junction Thermocouple on page 137 .
Figure 50 - Grounded Junction Thermocouple
ATTENTION: Take care when choosing a thermocouple junction, and
connecting it from the environment to the module. If you do not take
adequate precautions for a given thermocouple type, the electrical
isolation of the module might be compromised.
Extension Wire
Metal Sheath
Measuring Junction
Connected to Sheath