NTC
Thermistor Theory
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Stability
and Reliability
of Thermistors:
The
issue of Long Term
Stability of components
is a critical one
in most temperature
sensing applications.
Systems Designers
are usually concerned
with developing
circuitry and thermistor
sensor specifications
which assure accurate,
long-term measurement
capability. It
is extremely important
therefore that
the Resistance
versus Temperature
characteristics
of the thermistors
used in such critical
applications do
not change or drift
over time.
BetaTHERM’s
range of BetaCurve
product exhibit
very low drift
in the R/T characteristic
with respect to
time at elevated
temperatures. This
is indicated in
the table below.
The
long-term stability
is achieved by
control of materials
in the manufacturing
process and by "ageing" the
chips at elevated
temperatures prior
to assembly.
Information on stability
with respect to time is
included in the product
section of the catalog
for relevant products.
For
customized applications,
BetaTHERM can provide
advice on aging
methods and on
the selection of
products with optimum
long term stability.
AgingTime
(years) at
75°CFor Material
# 3
|
Change
in resistance
value  R
% |
Change
in temperature
value d
% |
| (Initial)
0 |
0.00 |
0.000 |
| 1 |
+
0.05 |
-
0.011 |
| 2 |
+
0.10 |
-
0.022 |
| 3 |
+
0.15 |
-
0.033 |
| 4 |
+
0.20 |
-
0.044 |
| 5 |
+
0.25 |
-
0.056 |
| 6 |
+
0.30 |
-
0.067 |
| 7 |
+
0.35 |
-
0.077 |
| 8 |
+
0.40 |
-
0.087 |
| 9 |
+
0.45 |
-
0.097 |
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Table
# 4 |
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For
applications where
tolerance and stability
are critical, BetaTHERM’s
BetaCURVE series
of products are
superior to the
BetaCHIP range.
Most manufacturers
offer ranges of
product that are
classified as either
high precision
and high stability
or low precision
devices. It is
generally more
economical to use
low precision components
where possible,
but for more critical
applications it
is advisable to
use high precision
devices.
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