Spectrum Controls 1769sc-IF8u - Manual (Page 105)

Appendix D Appendix D Appendix D Appendix D Appendix D
Using Using Using Using Using TTTTTher her her her hermocouple J mocouple J mocouple J mocouple J mocouple Junctions unctions unctions unctions unctions
This appendix describes the types of thermocouple junctions available, and
explains the trade-offs in using them with the 1769-IF8u thermocouple/mV
analog input module.
! A A A A ATTENTION TTENTION TTENTION TTENTION TTENTION 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
Using a Using a Using a Using a Using a
G r o u n d e d G r o u n d e d G r o u n d e d G r o u n d e d G r o u n d e d
J u n c t i o n J u n c t i o n J u n c t i o n J u n c t i o n J u n c t i o n
T TT T T h e r h e r h e r h e r h e r m o c o u p l e m o c o u p l e m o c o u p l e m o c o u p l e m o c o u p l e
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.
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 channel-
to-channel isolation is removed, since there is no isolation between signal