Spectrum Controls 1756sc-IF8u - Manual (Page 109)

Using Grounded Junction,
Ungrounded Junction, and Exposed
Junction Thermocouples
This appendix describes the types of thermocouples available, and explains
the trade-offs in using them with the IF8u module.
Thermocouple
Types
There are three (3) types of thermocouple junctions:
• Grounded Junction - The measuring junction is physically connected to
the protective sheath forming a completely sealed integral junction. If
the sheath is metal (or electrically conductive) then 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.
• Ungrounded Junction - The measuring junction is electrically isolated
from the protective metal sheath. This may also be referred to as an
insulated junction. This type is often used where noise would affect the
reading and for frequent or rapid temperature cycling. The response
time is longer than the grounded junction.
• Exposed Junction - The measuring junction does not have a protective
metal sheath so it is exposed. This junction style provides the fastest
response time but leaves the thermocouple wires unprotected against
corrosive or mechanical damage.
Appendix C