NI 9219E Operating Instructions and Specifications
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3-Wire RTD Mode
In 3-Wire RTD mode, the NI 9219E sources a current, which varies
based on the resistance of the load, between the EX+ and EX–
terminals. This mode compensates for lead wire resistance in
hardware if all the lead wires have the same resistance. The
NI 9219E applies a gain of 2x to the voltage across the negative
lead wire and the ADC uses this voltage as the negative reference
to cancel the resistance error across the positive lead wire.
Figure 9.
Connections in 3-Wire RTD Mode
LO
EX+
EX–
RTD
Wire
Wire
Wire
I
x2
ADC
I
I
NI 9219E
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