National Instruments NI 9234, Начало работы

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Connecting Grounded Differential Signals
You can connect grounded differential signals to the NI-9234.
Figure 3. Connecting Grounded Differential Signals to the NI-9234
NI 9234
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Signal
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Common
Voltage
Mode
Related concepts
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Overvoltage Protection
Common-Mode Bias Current
The NI 9234 uses common-mode bias current to bias the current-limiting diodes
when IEPE current is turned off. When the NI 9234 is using grounded signal sources,
this current causes an error that is dependent on the AI- lead impedance. This error
is approximately 50 ppm of range and 15 ppm of reading per ohm of AI- impedance.
The common-mode bias current causes an error only with grounded sources and is
not an issue with floating signal sources. For best accuracy, use low-impedance
leads when connecting grounded signal sources.
Figure 4. Measurement Error Introduced by Common-Mode Bias Current
NI 9234
AI+
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Signal
Source
AI– Lead
Impedance
Common
Mode
Bias
Current
IEPE Excitation Current
The NI 9234 can also provide an IEPE excitation current for each channel to measure
ground-referenced or floating IEPE sensors. Typical IEPE sensors have a case that is
electrically isolated from the IEPE electronics, so connecting the sensor to the NI
9234 results in a floating connection even though the case of the sensor is
grounded.
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NI-9234 Getting Started