National Instruments NI USB-9219 - Manual (Page 13)

© National Instruments Corporation 13 NI USB-9219 User Guide and Specifications
NI USB-9219 Timing Options
The NI USB-9219 supports four different timing options that are optimized
for different types of applications by using different ADC conversion
times. High Speed is optimized for high speed at the expense of noise
rejection, Best 60 Hz Rejection is optimized for rejection of 60 Hz noise,
Best 50 Hz Rejection is optimized for rejection of 50 Hz noise, and High
Resolution is optimized for maximum overall noise rejection and provides
good rejection of 50 Hz and 60 Hz noise. Refer to the
Specifications section
for more information.
NI USB-9219 Circuitry
The NI USB-9219 is channel-to-channel isolated. Four 24-bit
analog-to-digital converters (ADCs) simultaneously sample all four analog
input channels. An excitation circuit is enabled for all input modes that
require excitation. The ADC and excitation circuits are reconfigured in
each mode to accommodate each type of sensor. Refer to Figure 10 for an
illustration of the input circuitry for one channel of the NI USB-9219.
Figure 10. Input Circuitry for One Channel
Voltage and Current Modes
In Voltage and Current modes, connect the signal source to the
NI USB-9219 across the HI and LO terminals. The current is computed
from the voltage that the ADC measures across an internal shunt resistor.
Refer to Figure 11 for an illustration of the connections.
Figure 11. Connections in Voltage, Current, and Digital In Modes
Isolated
ADC
TEDS
1
2
+
–
CHx
3
6
NI USB-9219
Filter MUX
Current Mode
HI
LO
ADC I R
SH
NI USB-9219
Voltage/Digital In Modes
HI
LO
ADC V
+
–
NI USB-9219