Introduction To Thermistors - National Instruments NI 435 Series User Manual

Chapter 2 Operating the NI 435x Device
Note For best results, use the 1 mA current source when using the NI 4351 with RTDs
with resistances below 1 kΩ . Refer to the
software issues regarding the 1 mA source. For resistances above 1 kΩ or with the NI 4350,
use the 25 µA current source to avoid self-heating. Refer to the
further details.

Introduction to Thermistors

NI 435x User Manual
R
RTD
R
R
R
Figure 2-7. 3-Wire RTD Measurement and Lead Wire Resistance Compensation
Refer to Figure 2-10 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, which is 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 commonly used
than PTC thermistors, especially for temperature measurement
applications.
I
EX+
L1
CH n +
CH n –
L2
CH
CH
L3
I
EX–
= R – R if R
RTD CH n CH (n +1 )
file found on the NI 435x CD for
readme.htm
2-18
, I , or I
EX0+ EX1+
n +1
n +1
, I , or I
EX0– EX1–
= R = R
L1 L2 L3
Self-Heating section for
ni.com