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National Instruments Corp.
9
NI 9214 Operating Instructions and Specifications
Yo
u
can connect thermoco
u
ple inp
u
t signals to the NI 9214.
Connect the positive lead of the thermoco
u
ple to the TC+ terminal
and the negative lead of the thermoco
u
ple to the TC– terminal. If
yo
u
are
u
ns
u
re which of the thermoco
u
ple leads is positive and
which is negative, check the thermoco
u
ple doc
u
mentation or the
thermoco
u
ple wire spool.
The NI 9214 also has two common terminals, COM, that are
internally connected to the isolated gro
u
nd reference of the
mod
u
le. A connection to COM is not necessary for most
applications. Specifically, leave COM
u
nconnected for
config
u
rations in which all thermoco
u
ples are floating, all
thermoco
u
ples are referenced to the same common-mode voltage,
or one thermoco
u
ple is referenced to a common-mode voltage and
all others are floating.
However, for config
u
rations in which two or more thermoco
u
ples
are referenced to
different
common-mode voltages, connecting
COM according to the following g
u
idelines improves
common-mode rejection performance. Connect COM to chassis
gro
u
nd if the common-mode to chassis voltages are smaller than
±1.2 V. Otherwise, connect COM to a valid common-mode voltage
reference that is within ±1.2 V of the common-mode voltages of all
the thermoco
u
ple inp
u
ts.
NI_9214.fm Page 9 Monday, November 1, 2010 9:52 AM