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National Instruments Corp.
17
NI 9214 Operating Instructions and Specifications
Cold-Junction Temperature Measurement Accuracy
The NI TB-9214 has three cold-j
u
nction compensation channels.
Heat dissipated by adjacent mod
u
les or other nearby heat so
u
rces
can ca
u
se errors in thermoco
u
ple meas
u
rements by heating
u
p the
NI 9214 terminals to a different temperat
u
re than the cold-j
u
nction
compensation sensor. The thermal gradient across the terminals
can ca
u
se the terminals of different channels to be at different
temperat
u
res, in which case the res
u
lting meas
u
rement creates
errors not only in absol
u
te acc
u
racy b
u
t also in the relative
acc
u
racy between channels. Refer to the
section for
the cold-j
u
nction compensation acc
u
racy specifications. The
thermoco
u
ple acc
u
racy specifications incl
u
de the errors ca
u
sed
by the thermal gradient across the NI 9214 terminals for
config
u
rations with the NI 9214 terminals facing forward or
u
Temperature Measurement Accuracy
section
section for the thermoco
u
ple acc
u
racy
specifications.
Minimizing Thermal Gradients
Thermal gradients can be ca
u
sed by changes in the ambient air
temperat
u
re near the front connector or by the thermoco
u
ple wire
if it cond
u
cts heat or cold directly to the terminal j
u
nctions. For the
NI_9214.fm Page 17 Monday, November 1, 2010 9:52 AM