Appendix B Using Thermocouple Junctions; Section B.1 Using A Grounded Junction Thermocouple - Spectrum Controls 1769 Series User Manual

WARNING
Section B.1
Using a Grounded
Junction
Thermocouple
Appendix B
Using Thermocouple
Junctions
This appendix describes the types of thermocouple junctions available and
explains the trade-offs in using them with the 1769sc-IT6I Isolated
thermocouple/mV analog input module.
HAZARD OF ELECTRICAL SHOCK
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.
Available thermocouple junctions are:
• Grounded
• Ungrounded (isolated)
• Exposed
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 B-3.
The shield input terminals for a grounded junction thermocouple are connected
together and then connected to chassis ground. Use of this thermocouple with an
electrically conductive sheath removes the thermocouple signal to chassis ground
User's Manual Pub. 0300244-02 Rev. A