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National Instruments Corp.
15
NI 9214 Operating Instructions and Specifications
Each thermoco
u
ple channel also has a resistor between the
TC+ and COM terminals and between the TC– and COM
terminals. Beca
u
se long thermoco
u
ple wires can act like resistors,
the bias c
u
rrent from the OTD circ
u
it can ca
u
se small offset errors.
The gain and offset errors
res
u
lting from the so
u
rce impedance of
connected thermoco
u
ples
are negligible for many applications.
Thermoco
u
ples with a higher lead resistance can introd
u
ce more
significant errors. Refer to the
section for information abo
u
t compensating for offset errors
ca
u
sed by bias c
u
rrent and lead resistance. Refer to the
section for more information abo
u
t errors res
u
lting
from so
u
rce impedance.
The channels share a common gro
u
nd, COM, that is isolated from
other mod
u
les in the system. The NI 9214 common-mode range is
the maxim
u
m voltage allowed between any channel and COM. The
NI 9214 meas
u
res the common-mode voltage level of each channel
and ret
u
rns a warning in the software if the signal is o
u
tside the
common-mode voltage range. Refer to the
section
for more information abo
u
t the common-mode voltage range.
The NI 9214 s
u
pports high-resol
u
tion and high-speed timing
modes. High-resol
u
tion timing mode optimizes acc
u
racy and noise
and rejects power line freq
u
encies. High-speed timing mode
NI_9214.fm Page 15 Monday, November 1, 2010 9:52 AM