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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