Ni Pxie-4339 Block Diagram; Figure 2-18. Ni Pxie-4339 Signal Conditioning Block Diagram - National Instruments SC Express NI PXIe-4339 User Manual

NI PXIe-4339 Block Diagram

Figure 2-18 shows the analog input circuitry block diagram of the NI PXIe-4339. The
NI PXIe-4339 has two measurement modes. Voltage mode is used to measure voltages and
ratiometric mode is used to provide excitation and measure from bridge-based sensors. The
programmable excitation block provides the excitation voltage for bridge-based sensors. The
excitation voltage level is configurable on a per channel basis. In ratiometric mode, the
excitation voltage is sensed locally or remotely via the remote sense terminals (RS+ and RS-)
and fed back to the ADC (Analog-to-Digital Converter) reference through a programmable gain
amplifier. The gain applied when sensing the excitation voltage is automatically selected based
on the selected excitation voltage level and user specified input range.

Figure 2-18. NI PXIe-4339 Signal Conditioning Block Diagram

The bridge output voltage is sensed through the AI+ and AI- pins and then amplified and filtered
before being fed into the ADC input. The ADC then performs a ratiometric measurement of the
input signal versus the reference signal to determine the actual deflection of the bridge or sensor.
In voltage mode, the ADC voltage reference is fed by a stable 2.5 V voltage source.
I/O
Connector
EX +
RS +
RS –
EX –
AI +
x1, x20,
x50, x100
AI –
AO+
SCA
10 kΩ
SCA
T +
TEDS
T –
Interface
+
Programmable
–
Gain=1
or 0.25
2.5 V
Analog
Anti-Alias
Filter
Gain = 0.25
NI PXIe-4339 User Manual
Excitation
Reference
ADC
Input
x 8 Channels
© National Instruments | 2-23