©
National Instruments Corp.
13
NI 9219E Operating Instructions and Specifications
4-Wire Resistance and 4-Wire RTD Modes
In 4-Wire Resistance and 4-Wire RTD modes, the NI 9219E
sources a current, which varies based on the resistance of the load,
between the EX+ and EX– terminals. The NI 9219E computes
measured resistance from the resulting voltage reading. Lead wire
resistance does not affect these modes because a negligible amount
of current flows across the HI and LO terminals due to the high
input impedance of the ADC.
Figure 8.
Connections in 4-Wire Resistance and 4-Wire RTD Modes
LO
HI
EX–
RTD/
Resistor
Wire
Wire
Wire
I
ADC
I
EX+
Wire
NI 9219E
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