National Instruments 6368, Руководство пользователя

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Chapter 4 Analog Input
Analog Input Ground-Reference Settings
MIO X Series devices support the following analog input ground-reference settings:
•
Differential mode
—In DIFF mode, the MIO X Series device measures the difference in
voltage between two AI signals.
• Referenced single-ended mode —In RSE mode, the MIO X Series device measures the
voltage of an AI signal relative to AI GND.
•
Non-referenced single-ended mode
—In NRSE mode, the MIO X Series device measures
the voltage of an AI signal relative to one of the AI SENSE inputs specific for that channel.
The AI ground-reference setting determines how you should connect your AI signals to the MIO
X Series device. Refer to the
Connecting Analog Input Signals section for more information.
Ground-reference settings are programmed on a per-channel basis. For example, you might
configure the device to scan 12 channels—four differentially-configured channels and eight
single-ended channels.
MIO X Series devices implement the different analog input ground-reference settings by routing
different signals to the NI-PGIA. The NI-PGIA is a differential amplifier. That is, the NI-PGIA
amplifies (or attenuates) the difference in voltage between its two inputs. The NI-PGIA drives
the ADC with this amplified voltage. The amount of amplification (the gain), is determined by
the analog input range, as shown in Figure 4-2.
Figure 4-2.
MIO X Series Device NI-PGIA
V
in+
V
m
= [V
in+
– V
in–
]
×
Gain
V
m
V
in–
PGIA
+
–
Measured
Voltage