NI 9234E Operating Instructions and Specifications
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© National Instruments
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9
Figure 5.
NI 9234E Input Circuitry for One Channel
The NI 9234E uses common-mode bias current to bias the
current-limiting diodes when IEPE current is turned off. When the
NI 9234E 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
Ω
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 a floating connection or use
low-impedance leads when connecting grounded signal sources.
2 mA IEPE on/off
AI+
AI–
Amplifier
a
nd
Prefilter
ADC
+
–
AC/DC Co
u
pling
NI 92
3
4E
Common
Mode
Bi
as
C
u
rrent
C
u
rrent
Limiting
Diode
s
50
Ω
