NTC
Thermistor Theory
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Specification
of thermistors
for applications:
The
preceding sections
have covered topics
relating to the
factors that affect
the measured value
of resistance of
a thermistor and
to issues that
affect the correlation
between this measured
resistance value
and temperature
of the thermistor.
The next major
topics concern
the specification of
thermistors and
the implementation
of applications that
use thermistors.
The specification of
thermistors in
terms of part numbers
and product ranges
is dealt with in
the product
section. This
section provides
information on
the specification
of Material Curve
number, nominal
resistance value,
tolerances, lead
wire options and
associated factors.
All of these attributes
affect the performance
of a thermistor
in an application.
For situations where the
specification of a component
part-number are not
clear-cut, BetaTHERM applications
engineering group can provide
advice and customer support.
In
terms of applications,
thermistors represent
a mature product
range and there
are many "standard" application
methods in existence.
However, it can
be difficult to
find information
on specific aspects
of thermistor applications,
as the published
literature on the
topic is diverse
and not well catalogued.
The
application notes
that are in the next
sections attempt
to address this
situation. While
an in-depth discussion
at text-book level
is beyond the scope
of the catalog,
the application
notes provide a
general overview
of methods of using
thermistors and
provide key words
and headings that
may serve as pointers towards
more detailed sources
of information.
The applications section
concludes with some notes
on interfacing thermistors
to instrumentation. This
section is also presented
as an overview of some
relevant topics, so that
the key-words and headings
can be used to source more
detailed information on
particular items.
Thermistor applications
make use of the basic thermistor
features, such as Resistance
versus Temperature characteristics,
zero-power characteristics,
self heating effects and
thermal characteristics
like heat capacity and
dissipation constant. It
follows that a knowledge
of these factors is important
in understanding principles
of thermistor applications.
Once the general principle
of an applications is understood,
then the concepts of tolerance
and stability and product
specification become relevant
in selecting the actual
component to be used in
the application.
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