National Instruments Module SCXI-1503 Manuel d'utilisateur télécharger pdf (Page 17)

Chapter 2 Connecting Signals

SCXI-1503 User Manual 2-4 ni.com

2-Wire Configuration

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

excitation current (I

) times the sum of the two lead resistances, R

and

. If we assume equal lead resistances, R

= R

, the magnitude of

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.

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

CH X

–

SCXI-1306External Sensor SCXI-1503

Channel X

IEX+

AI+

AI–

IEX–

I = 100 µA

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National Instruments Module SCXI-1503 Manuel d'utilisateur Page 17