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

Section B.1
Using a Grounded
Junction
Thermocouple
User's Manual Pub. 0300244-01 Rev. A
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.
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
Attention
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 isolation of the
module. In addition, if multiple grounded junction thermocouples are used, the module