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Operating as a Matrix
© National Instruments Corporation
where T(°F) and T(°C) are the temperature readings in degrees Fahrenheit
and degrees Celsius, respectively.
Making RTD Measurements
Figure 2-16 shows an RTD (R
terminal block. The RTD is connected in the four-wire configuration. It is
recommended that you connect RTDs in a four-wire configuration to
eliminate the effects of lead resistance on the measurement. See the
Four-Wire versus Two-Wire Resistance Measurement
information.
Making Thermistor Measurements
Figure 2-16 shows a thermistor (R
SCXI-1331 terminal block. The thermistor is connected in the two-wire
configuration. You can connect the thermistor in the two, four, or even
one-wire input configurations. The choice is typically dictated by channel
cost and required accuracy. The four-wire configuration is ideal and
provides the best accuracy, while one-wire provides the maximum channel
count. Use the four-wire configuration to eliminate the effects of lead
resistance on the measurement. Since the lead resistance is typically small
when compared with the thermistor range, the impact of the lead resistance
error is smaller than you have in an RTD measurement. See the
versus Two-Wire Resistance Measurement
A matrix is one of the most flexible switching configurations. Unlike a
multiplexer, a matrix can connect multiple inputs to multiple outputs. A
multiplexer is typically organized into channels and commons, while a
matrix is organized into columns and rows. You can connect any column
to any number of rows and any row to any number of columns. Figure 2-17
shows an example of a 4x2 one-wire matrix configuration. At each
intersection of a row and column, there is a switch. When the switch is
closed, the row is connected to the column. Figure 2-17 depicts a one-wire
matrix; the SCXI-1127 is a two-wire matrix. The switching method for a
two-wire matrix remains the same. A two-wire matrix is shown in
[T(°C ) ]9
T °F
(
)
=
-----------------------
5
) connected to channel 12 on the SCXI-1331
1
) connected to channel 24 on the
2
2-19
Chapter 2
Using the SCXI-1127
+
32
section for more
Four-Wire
section for more information.
SCXI-1127 User Manual
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