2-Wire Configuration; Figure 2-2. 2-Wire Resistive Sensor Connected In A 2-Wire Configuration - National Instruments Module SCXI-1503 User Manual

Chapter 2 Connecting Signals

2-Wire Configuration

SCXI-1503 User Manual
The basic 2-wire configuration is shown in Figure 2-2. In this configuration
an error voltage (V ) is introduced into the measurement equal to the
E
excitation current (I
EX
R . If we assume equal lead resistances, R
L2
the error voltage is:
This is the most commonly used configuration for connecting thermistors
to a signal conditioning system because the large sensitivity of thermistors
usually results in the introduction of a negligible error by the lead
resistances.
RTDs typically have a much smaller sensitivity and nominal resistance than
thermistors, therefore a 2-wire configuration usually results in the
introduction of larger errors by the lead resistance.
External Sensor
R
L1
R
T
R
L2

Figure 2-2. 2-Wire Resistive Sensor Connected in a 2-Wire Configuration

) times the sum of the two lead resistances, R
L1
V 2R I
=
E L EX
SCXI-1306
IEX+
AI+
AI–
IEX–
CH X
ON
2-4
= R = R , the magnitude of
L2 L
SCXI-1503
Channel X
+
I = 100 µA
–
and
L1
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