User Manual
Appendix DAppendix D
Appendix DAppendix D
Appendix D
Using Using
Using Using
Using
TT
TT
T
herher
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mocouple Jmocouple J
mocouple Jmocouple J
mocouple J
unctionsunctions
unctionsunctions
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.
!
AA
AA
A
TTENTION 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 aUsing a
Using aUsing a
Using a
GroundedGrounded
GroundedGrounded
Grounded
JunctionJunction
JunctionJunction
Junction
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T
herher
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her
mocouplemocouple
mocouplemocouple
mocouple
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