National Instruments NI 9214, Инструкция по эксплуатации и технические характеристики, Страница: 15 / 44

© 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 Compensating for OTD Current
section for information abo u t compensating for offset errors
ca u sed by bias c u rrent and lead resistance. Refer to the
Specifications 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 Specifications 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
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