AAS-930-164B Datasheet, PDF (2/4 Pages) Amphenol Corporation – Thermopile IR Sensor Applications

Applications Considerations
Specific Detectivity
Package
The NEP is convenient for predicting the maximum
power a given system can detect, but it has some
undesirable features:
• A good thermopile detector will have a small NEP.
• The thermopile detectors of different sizes will
have different NEPs.
So we cannot say, in general, what a good NEP
should be, unless we specify the size of thermopile
detector.
Detectivity has been introduced to include device
noise and sensitivity simultaneously. It is usually
normalized with respect to detector size and noise
bandwidth, and the resulting specific detectivity, D*,
is defined by:
Our thermopile detector is packaged with silicon
filter and thermistor as shown below. We are
supplying TO-5 package and TO-46 package as the
standard type , but on request, other package types
are also available.
Detector Packaging
A large D* is good, and for a given environment all
good detectors should have almost the same D*.
Noise
The thermopile detector noise is another important
factor determining the detector performance.
There are many noise sources in a thermopile
detector. A fundamental noise is caused by actual
temperature fluctuations.
A theoretical limit of thermopile sensitivity will be
determined when this noise is at its minimum.
In this thermopile detector, Johnson noise of these
many noise sources is a predominant electrical
noise source. Since the device impedance for
a typical thermopile detector is mainly resistive,
the Johnson noise for a detector having a device
resistance R is:
Where B is the noise bandwidth. At low frequency,
flicker noise originating from contacts or other
sources may be dominants, and, depending upon
the sensing materials, shot noise may also be
involved. Typically, Johnson noise is the most im-
portant of these electrical noise sources for most
thermopile detectors.
(1) Thermistor for the compensation of an environ-
ment temperature
According to the variation of an environment tem-
perature, the output of thermopile detector is also
varying. It is therefore need to compensate this
temperature performance of thermopile detector.
Our thermopile detectors are using a thermistor for
the compensation of an environment temperature,
and we have also a variety of thermistors enough for
pursuing customer’s need.
(2) Windows Filter
In order to improve the thermopile detector
performance, it is also a very important factor to
select suitable filter for a given application. We are
basically using a broadband-silicon filter of which
the transmittance is 6-13um.
But when there is an application for an
optical system, the preparation of proper filter
specifications is also of prime importance for the
optimum performance. Therefore we are available
for many typical infrared filters -not only a broad
band pass filters (BBP) but also a narrow band pass
filters (NBP).
The following specifications will assist an engineer
who designs the optical system.
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