Introduction To Thermistors - National Instruments NI 4350 User Manual

Chapter 3 NI 4350 Operation

Introduction to Thermistors

NI 4350 User Manual
R
RTD
R
R
Figure 3-6. Three-Wire RTD Measurement with a Wheatstone Bridge
Figure 3-7. Three-Wire RTD Measurement
See Figure 3-10 for an example of how you can use different
transducers connected to analog channels in the same measurement
setup.
A thermistor is a piece of semiconductor made from metal oxides,
pressed into a small bead, disk, wafer, or other shape, sintered at high
temperatures, and finally coated with epoxy or glass. The resulting
device exhibits an electrical resistance that varies with temperature.
There are two types of thermistors—negative temperature coefficient
(NTC) thermistors and positive temperature coefficient (PTC)
thermistors. An NTC thermistor is one whose resistance decreases with
increasing temperature. A PTC thermistor is one whose resistance
increases with increasing temperature. NTC thermistors are much more
L1
L2
CH+ CH–
L3
R
R
3
and a Current Source
R
L1
RTD
R
L2
R
L3
3-18
IEX+
R
1
2
IEX–
IEX+
CH+
CH–
IEX–
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