Dexter Research: An Introduction to Thermopile Detectors

Thermopile
Thermopile
Detectors
Detectors
An Introduction to

5 ARTICLE
An Introduction to Thermopile
Detectors
9 ARTICLE
An Overview of Thermopile Detectors
12 ARTICLE
Encapsulation Gas in Thermopile
Detectors
18 ARTICLE
Determining the Thermopile Time
Constant
20 ARTICLE
What are Thermophile Detectors Used
for?
23 ARTICLE
Thermopile Detectors for Gas
Measurement and Analysis
T A B L E O F
C O N T E N T S

Introduction
Introduction
Welcome to the fascinating world of
thermopile detectors. Since the invention
of the first thermopile by Macedonio
Melloni in 1830, the field of radiation
sensing technology has witnessed an
evolution marked by groundbreaking
advancements.
In this concise ebook, brought to you by the
Dexter Research Center (DRC), we embark on
a journey to unravel the intricacies of
thermopile detectors, highlighting their various
applications, and revealing their pivotal role
across diverse industries.
Infrared thermopile detectors represent the
pinnacle of technological advancement in
temperature measurement. Learn about
infrared radiation, the advantages and
limitations of thermopiles, as well as the
superiority of these devices over other infrared
sensors in this incisive chapter.
Delving deeper, we investigate the crucial role
of encapsulating gas in optimizing the
performance of thermopile detectors.
Focusing on key performance parameters for
silicon- and thin film-based thermopiles and
encapsulation gas calculations for Dexter’s
models, we break down how encapsulating
gas influences the efficiency and reliability of
thermopile detectors.
Unlocking the secrets of thermopile detectors
entails mastering the measurement of their
time constant. Through various
methodologies and practical insights, gain an
understanding of how to accurately determine
the time constant—a vital aspect in ensuring
the precision and effectiveness of thermopile
detectors.
Chapter 1: An Introduction to
Thermopile Detectors
Chapter 2: An Overview of
Chapter 3: Encapsulation Gas in
Chapter 4: Determining the
Thermopile Time Constant
Our journey begins with an overview of
thermopile detectors. In this chapter, we
unpack the fundamental components of
thermopiles, explore the different types of
detectors, discuss the specialized offerings by
DRC, and touch upon some common
thermopile applications. In doing so, we lay
the groundwork for understanding the core
principles behind these remarkable
instruments.

We round our tour of thermopiles by
evaluating their application in the specialized
domain of gas measurement and analysis.
Discover how these detectors assist early
warning systems, trace-level detection, and
sophisticated gas analysis, revolutionizing
industries from environmental monitoring to
healthcare. Finally, learn about Dexter’s range
of customizable detectors designed to meet
the diverse needs of modern applications,
providing unmatched precision, reliability, and
adaptability.
Chapter 5: What are Thermophile
Detectors Used for?
Chapter 6: Thermopile Detectors
for Gas Measurement and Analysis
Venturing into operational principles for
thermopile detectors, we then survey their
diverse applications across industries. From
aerospace processes and automotive
workflows to medical diagnostics and solar
cell monitoring, uncover the myriad ways
thermopile detectors boost efficiency, safety,
and precision in numerous domains.
As Dexter Research Center guides you on this enlightening journey through the world
of thermopile detectors, prepare to expand your knowledge, gain valuable insights,
and uncover the boundless possibilities that these extraordinary devices offer.
F I N D O U T M O R E

An Introduction to ermopile Detectors
A thermopile detector is a passive radiation sensing voltage-generating device. It
does not emit any radiation and require cooling or bias. Dexter Research Center
(DRC) provides stable, high output radiation sensing thermopile detectors covering
linear dynamic range from the UV to long wave IR.
The spectral absorption of DRC detectors is flat from the ultraviolet to the far infrared.
Based on target size, radiance and temperature, the output of thermopiles is typically in the
range of microvolts to millivolts.
Key Components of Thermopile Detectors
Thermopile detectors consist of an array of thermocouple junctions linked in series as
differential pairs. These differential pairs form the hot and cold junctions as shown in Figure
1.
Alternating n-type and p-type materials called ‘Arms’ connect these junctions and generate
a Seebeck effect between them. A voltage is generated in proportion to the temperature
gradient between the cold and hot junctions.
Figure 1. Key features of the Model 2M Thin Film thermopile detector
Bismuth and antimony are the arm materials for thin film-based thermopiles. Alternating n-
type and p-type poly-silicon or n-type with aluminum or gold are the arm materials for
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silicon thermopiles. The cold junctions and the detector package are normally thermally
connected. These junctions are positioned around the perimeter of the substrate opening.
The hot junctions have a coating of an energy absorber and are positioned in the center of
the detector pattern. The detector’s active area is defined by these hot junctions, which are
thermally isolated from the rest of the package by means of a thin membrane.
It is necessary to know the detector cold junction temperature to perform a radiometrically
calibrated measurement with a thermopile detector. This can be done by determining the
temperature of the detector package using a thermistor or active device like a LM20 from
National Semiconductor.
Most accurate temperature measurements are possible when the thermistor or other device
is thermally connected to the detector package and is in the proximity to the detector.
Thermopile detectors have very low noise at the level of a resistor of equal resistance. They
generate only the Johnson noise of their resistance and yield a consistent output for DC
radiation up to a frequency restricted by the time constant. In addition, they do not require
chopper.
DRC Thermopile Detectors
DRC thermopile detectors are in tiny TO-18, TO-5, or TO-8 transistor type packages. The
ambient air is removed from the detector package and one of the four encapsulating gases
is then filled in prior to hermetically sealing the package. The encapsulating gas presents
one of the key thermal paths to dissipate energy from the active area.
DRC detectors have a flat spectral response over the ultraviolet to the far infrared owing to
the use of unique energy absorbing materials. The selection of optical band-pass filters
decides spectral sensitivity depending on the application of the detector.
Besides having a variety of optical filters and window materials, DRC can customize them
depending on the detector application. Internal heatsinks, optional internal apertures, and
different options of package aperture sizes are also offered by Dexter Research to address
the design requirements of customers.
Types of Thermopile Detectors
Bismuth-Antimony silicon-based and thin film-based are the types of thermopile detectors
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offered by DRC. The resistance and noise voltage of thin film-based thermopiles are lower
when compared to silicon-based thermopiles, thus providing a higher signal-to-noise ratio.
The time constant of a thin film thermopile with an output equivalent to a silicon-based
thermopile is comparatively slower. The active area of thin film thermopiles is typically large.
The following table compares the two types of thermopiles:
Parameter Thin Film Silicon
Output Voltage Higher Lower
Signal-to-Noise Ratio Higher Lower
Temperature Coefficient of ℜ -0.36%/°C -0.04%/°C
Noise Voltage Lower Higher
Time Constant Slower Faster
Cost Higher Lower
Operating Temperature 100°C 125°C*
* Specific configurations to 225°C
An internal compensating element is available in most of the thin film thermopiles and is
blinded. It is generally linked in opposition to the active element to reduce the effect of an
unexpected change in ambient package temperature.
This temperature compensation is useful for roughly the first few seconds of thermal shock
to the detector package. Compensated silicon thermopiles are also available from DRC.
DRC also supplies different kinds of thermopile detector modules with digital output. The
company’s silicon thermopile detector technology is the cornerstone of its Temperature
Sensor Module (TSM) , which consists of an integrated ASIC in the detector package to
yield a calibrated digital output for precise non-contact temperature measurements.
Applications of Thermopile Detectors
Thermopile detectors find use in the following applications:
Non-contact temperature measurements in process control and industrial applications
Hand-held non-contact temperature measurements
Thermal line scanners
Tympanic Thermometers Infrared Radiometry Refrigerant Leak Detection
Automotive exhaust gas analysis of HC, CO and CO
Commercial building HVAC and lighting control
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Security human presence and detection
Black ice detection and early warning
Blood glucose monitoring
Horizon sensors for satellites, aircraft, and hobbyist applications
Medical gas analysis such as blood alcohol breathalyzers, incubator CO and CO ,
and anesthetic
Automotive occupancy sensing
Automotive HVAC control
Aircraft flame and fire detection
Fire detection in transportation tunnels
Hazard detection including flame and explosion
Household appliance temperature measurement
This information has been sourced, reviewed and adapted from materials provided by
Dexter Research.
For more information on this source, please visit Dexter Research.
2
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An Overview of ermopile Detectors
Infrared thermopile detectors are used for temperature measurements without direct
contact, relying on an object's infrared (IR) energy. These detectors consist of small
sensors called thermocouples, which generate an electric voltage when exposed to
IR.
In various industries, infrared thermopile detectors play a crucial role and often serve in
industrial manufacturing processes and environmental monitoring. This article introduces
infrared thermopile detectors, outlining their benefits and applications.
Image Credit: Ivan Smuk/Shutterstock.com
Understanding Infrared Radiation
Before delving into the operation of IR thermopile detectors, it is essential to grasp the
fundamentals of infrared radiation. Infrared radiation is a form of energy characterized by
wavelengths longer than visible light but shorter than radio waves, ranging from 780 nm to
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1 mm.
Although invisible to the human eye, it manifests as heat. Infrared radiation is emitted by
every object, aiding researchers in assessing properties such as heat distribution and
temperature fluctuations.
How Infrared Thermopile Detectors Work
Infrared thermopile detectors primarily consist of thermopile sensors based on the Seebeck
effect principle. As mentioned, these sensors comprise several thermocouples. Each
thermocouple consists of at least two wires made from different metals, with the wires
joined at one end to form a junction.
These wires produce a voltage proportional to the temperature gradient across their
junctions. This signal can be subsequently amplified, processed, and converted into
meaningful temperature data.
Advantages and Limitations of Infrared Thermopile
Detectors
Numerous advantages come with using infrared thermopile detectors, including the ability
to measure temperature without direct contact, facilitating remote sensing in challenging
environments. Their rapid response time allows real-time monitoring, and their heightened
sensitivity ensures the detecting of even slight temperature changes.
These detectors can also be sealed hermetically, safeguarding them from environmental
factors.
Recognizing Limitations
Despite their remarkable capabilities, infrared thermopile detectors do have certain
limitations. They typically operate within a specific spectral range, which can restrict their
suitability for particular applications.
Fluctuations in ambient temperature may impact accuracy, necessitating careful calibration
and compensation techniques. Evaluating these limitations when choosing an appropriate
detection solution is crucial, as they may not be suitable for every application.
Comparison with Other Infrared Detectors
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Infrared thermopile detectors offer distinct advantages over other types of infrared sensors,
such as bolometers or pyroelectric detectors. Thermopiles provide greater sensitivity, a
broader field of view, and enhanced temperature measurement capabilities, making them
ideal for various scientific and industrial applications.
Infrared Thermopile Detectors from Dexter Research
Centre
Dexter Research Center, a pioneer in infrared thermopile detectors since 1977, leads the
industry with a comprehensive selection of state-of-the-art thermopiles. The product line
comprises high-quality Bismuth-Antimony thin-film and silicon-based thermopile detectors
renowned for their exceptional performance and dependability.
Not only does the company offer an extensive range of standard products, but it also
specializes in custom thermopile detectors and modules. The company's expertise
guarantees tailored solutions for specific application requirements, while its dedication to
quality and reliability ensures unmatched performance.
Dexter Research Center, Inc.
For more information on this source, please visit Dexter Research Center, Inc.
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Encapsulation Gas in ermopile
Detectors
Time constant, signal-to-noise ratio (SNR), responsivity and output voltage are the
four key performance parameters affected based on the selection of an
encapsulating gas in a thermopile detector package.
The effect of the molecular thermal conductivity of gases on the thermal resistance of the
detector and package affects the time constant, responsivity and output voltage.
Thermopile model, type of package (resistance weld versus cold weld) and the amount of
black absorber are the other factors affecting these performance parameters.
The selection of the encapsulating gas has less impact on these three parameters in the
case of silicon-based thermopiles when compared to thin film-based thermopile detectors.
Encapsulation Gas Effect on Silicon- and Thin Film-
Based Thermopiles
The specifications presented in the Dexter Research Center (DRC) data sheets are for
nitrogen or argon encapsulation gas based on the detector model. The specifications of all
“ST” detectors are with nitrogen.
The specifications of all other models are with argon. These parameters vary by the same
percentage, approximated by the multipliers presented in Tables 1, 2, and 3, for thin film-
based, “S” type silicon-based, “ST” type silicon-based (thick rim) thermopiles, respectively.
As shown in Table 1, the use of encapsulating gas xenon in place argon in a detector
package will increase the time constant, responsivity and output voltage by 2.4 times in the
case of thin film-based thermopiles. Similarly, the increase in these parameters for “S” type
silicon-based thermopiles will be by 1.6 times as shown in Table 2.
Table 1. Output voltage, responsivity, SNR, and time constant multipliers for thin film-based
thermopile detectors relative to argon
Thin Film Based Thermopile in Argon (Ar)
Gas Multiplier
Nitrogen (N2) .75
Xenon (Xe) 2.4
Neon (Ne) .4
Table 2. Output voltage, responsivity, SNR, and time constant multipliers for “S” type
silicon-based thermopile detectors relative to argon
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“S” type Silicon Based Thermopile in Argon (Ar)
Gas Multiplier
N2 .87
Xe ~1.6
Ne 0.6
Table 3. Output voltage, responsivity, SNR, and time constant multipliers for “ST” type
silicon-based thermopile detectors relative to nitrogen
“ST” type Silicon Based Thermopile in Nitrogen (N2)
Gas Multiplier
Ar 1.1
Xe 1.55
Ne 0.9
Table 2 and 3 are for silicon-based thermopiles, of which “S” type silicon-based models
using argon as encapsulating gas (model S60M) are shown in Table 2. The “ST” type
silicon-based models with nitrogen (all multi-channel models) as encapsulating gas are
presented in Table 3. At present, the LCC package is only offered with nitrogen.
The multipliers shown in the aforementioned tables can differ by more than 25%. This
difference is restricted by the fact that if a multiplier is more than 1.0, then it cannot have a
value lower than 1.0. Similarly, if a multiplier is below 1.0, then it cannot have a value above
1.0. Argon, neon, xenon and nitrogen are the four standard encapsulating gas options
offered by DRC. For each gas, the effect varies based on the type of the detector.
The encapsulation gas calculations for Dexter thermopile detector models are summarized
in Table 4.
Table 4. Encapsulation gas calculations for Dexter thermopile detector models
Single-Channel
Argon
Output Voltage
(µV)
Signal-to-Noise Ratio
(Vs/Vn)
Time Constant
(ms)
M5 35.0 5,000 28.0
S60M TO-18 89.0 2,320 18.0
S60M TO-5 120.0 3,125 27.0
M14 20.0 2,857 14.0
ST60 Micro 59.4 1,896 19.8
ST60 TO-18 66.0 2,108 16.5
ST60 TO-5 68.2 2,179 19.8
ST60 with Lens 324.5 10,368 19.8
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1M 60.0 8,571 32.0
1SC Compensated 48.0 3,582 48.0
M34 115.0 10,088 38.0
DR34
Compensated
115.0 7,099 38.0
ST120 TO-5 198.0 5,161 27.5
ST150 253.0 7,228 41.8
ST150 with Lens 357.5 10,215 41.8
DR46
Compensated
210.0 11,602 40.0
2M 250.0 19,531 85.0
3M 440.0 25,581 100.0
6M 370.0 18,317 221.0
Multi-Channel
ST60 Dual 68.2 2,179 19.8
DR26 54.0 5,684 38.0
DR34 115.0 10,088 38.0
ST120 Dual 181.5 4,731 27.5
ST150 Dual 253.0 7,228 41.8
DR46 210.0 16,406 40.0
T34 Compensated 115.0 7,099 38.0
ST60 Quad 68.2 2,179 19.8
ST120 Quad 154.0 4,014 27.5
ST150 Quad 253.0 7,228 41.8
2M Quad 250.0 19,531 85.0
10 Channel 115.0 10,088 38.0
Single-Channel
Nitrogen
Output Voltage
(µV)
(Vs/Vn)
Time Constant
(ms)
M5 26.3 3,750 21.0
S60M TO-18 77.4 2,018 15.7
S60M TO-5 104.4 2,719 23.5
M14 15.0 2,143 10.5
ST60 Micro 54.0 1,724 18.0
ST60 TO-18 60.0 1,916 15.0
ST60 TO-5 62.0 1,981 18.0
ST60 with Lens 295.0 9,425 18.0
1M 45.0 6,428 24.0
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M34 86.3 7,566 28.5
DR34
Compensated
86.3 5,324 28.5
ST120 TO-5 180.0 4,692 25.0
ST150 230.0 6,571 38.0
ST150 with Lens 325.0 9,286 38.0
DR46
Compensated
157.5 8,702 30.0
2M 187.5 14,648 63.8
3M 330.0 19,186 75.0
6M 277.5 13,738 165.8
Multi-Channel
ST60 Dual 62.0 1,981 18.0
DR26 40.5 4,263 28.5
DR34 86.3 7,566 28.5
ST120 Dual 165.0 4,301 25.0
ST150 Dual 230.0 6,571 38.0
DR46 157.5 12,305 30.0
T34 Compensated 86.3 5,324 28.5
ST60 Quad 62.0 1,981 18.0
ST120 Quad 140.0 3,649 25.0
ST150 Quad 230.0 6,571 38.0
2M Quad 187.5 14,648 63.8
10 Channel 86.3 7,566 28.5
Single-Channel
Xenon
Output Voltage
(µV)
(Vs/Vn)
Time Constant
(ms)
M5 84.0 12,000 67.2
S60M TO-18 142.4 3,712 28.8
S60M TO-5 192.0 5,000 43.2
M14 48.0 6,857 33.6
ST60 Micro 83.7 2,672 27.9
ST60 TO-18 93 2,970 23.25
ST60 TO-5 96.1 3,071 27.9
ST60 with Lens 457.2 14,609 27.9
1M 144 .0 20,570 76.8
1SC Compensated 115.2 8,597 115.2
M34 276.0 24,211 91.2
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DR34
Compensated
276.0 17,038 91.2
ST120 TO-5 279 7,273 38.75
ST150 356.5 10,185 58.9
ST150 with Lens 503.7 14,393 58.9
DR46
Compensated
504.0 27,845 96.0
2M 600.0 46,874 204.0
3M 1056. 61,394 240.0
6M 888 .0 43,961 530.4
Multi-Channel
ST60 Dual 96.1 3,071 27.9
DR26 129.6 13,642 91.2
DR34 276.0 24,211 91.2
ST120 Dual 255.7 6,667 38.75
ST150 Dual 356 .5 10,185 58.9
DR46 504.0 39,374 96.0
T34 Compensated 276.0 17,038 91.2
ST60 Quad 96.1 3,071 27.9
ST120 Quad 217 5,656 38.75
ST150 Quad 356.5 10,185 58.9
2M Quad 600.0 46,874 204.0
10 Channel 276.0 24,211 91.2
Single-Channel
Neon
Output Voltage
(µV)
(Vs/Vn)
Time Constant
(ms)
M5 14.0 2,000 11.2
S60M TO-18 53.4 1,392 10.8
S60M TO-5 72.0 1,875 16.2
M14 8.0 1,143 5.6
ST60 Micro 48.6 1,552 16.2
ST60 TO-18 54 1,724 13.5
ST60 TO-5 55.8 1,783 16.2
ST60 with Lens 265.5 8,483 16.2
1M 24.0 3,428 12.8
M34 46.0 4,035 15.2
DR34
Compensated
46.0 2,840 15.2
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ST120 TO-5 162 4,223 22.5
ST150 207 5,914 34.2
ST150 with Lens 292.5 8,357 34.2
DR46
Compensated
84.0 4,641 16.0
2M 100.0 7,812 34.0
3M 176.0 10,232 40.0
6M 148.0 7,327 88.4
Multi-Channel
ST60 Dual 55.8 1,783 16.2
DR26 21.6 2,274 15.2
DR34 46.0 4,035 15.2
ST120 Dual 148.5 3,871 22.5
ST150 Dual 207 5,914 34.2
DR46 84.0 6,562 16.0
T34 Compensated 46.0 2,840 15.2
ST60 Quad 55.8 1,783 16.2
ST120 Quad 126 3,284 22.5
ST150 Quad 207 5,914 34.2
2M Quad 100.0 7,812 34.0
10 Channel 46.0 4,035 15.2
Time Constant and Output Voltage Calculations for DRC
model 2M
As shown in Table 4, the time constant for the DRC model 2M with argon encapsulating gas
is 85ms. The approximate time constant for the model 2M using xenon encapsulating gas
can be calculated by multiplying the time constant value of argon by 2.4 (xenon multiplier in
Table 1), which gives 204ms.
Similarly, the output voltage of the model 2M with argon encapsulating gas under exposure
to 330µW/cm radiation is 250µV (Table 4). By multiplying this value with xenon multiplier of
2.4 given in Table 1, the approximate test stand output voltage can be calculated for the
model 2M using xenon as encapsulating gas. The resulting output voltage for the 2M
encapsulated with xenon is 600µV.
Dexter Research.
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Determining the ermopile Time
Constant
There are several methods available to determine the time constant of thermopile
detectors based on the specific waveform of the radiation utilized in the excitation of
the detector. The response of a detector, when it is exposed to a step function of
radiation, follows the function V = V (1-e ), of which V is the output of the
detector at any time t.
The time taken when V reaches 63.2% of the maximum static value V is defined as the
time constant (τ) of the thermopile detector.
The frequency response of a thermopile detector when it is exposed to sinusoidally
modulated radiation follows the function:
V = V [1+(2πτ/T) ] ,
Where,
V = The dynamic amplitude of the output voltage of the detector at any wave period T
V = The static amplitude of the output voltage produced by un-modulated radiation
V decreases by 3dB (.707 Vs) from the static value during T , which is correlated to the
time constant of the thermopile detector by the following expression:
τ = T /kπ
Here, the value of the coefficient k is 2 for sinusoidally modulated signals. The waveform of
chopper-modulated radiation resembles a square wave and the corresponding value of k is
1.124.
Determination of Thermopile Time Constant
For both methods, a red LED can be employed when the thermopile window/filter transmits
in the visible spectrum. It is necessary to apply the appropriate coefficient based on the
waveform used. At Dexter Research Center (DRC) , the following methods have been used
to determine the time constant:
t max
-t/τ
t
t max
d s
2 -1/2
d
s
d o
o
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A square wave modulated red LED is used when the thermopile window/filter
transmits in the visible spectrum
A chopped blackbody is used when the thermopile window/filter does not transmit in
the visible spectrum
It is simple and quick to perform direct measurement of the approximate time constant
using a modulated signal. The peak-to-peak trace of the DC output of the thermopile
detector is adjusted to seven divisions on an oscilloscope utilizing a very slow modulation
frequency.
The frequency is increased until the peak-to-peak trace covers five divisions (.707 x 7div. =
4.95div.). This is roughly –3dB of V . It is then possible to determine the time constant
from the wave period or from the frequency by applying the suitable coefficient for the
waveform employed.
Dexter Research.
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What are ermophile Detectors Used for?
Thermopile detectors are used to measure the temperature of distant objects by
converting infrared (IR) radiation into an electrical signal. This primary function finds
use across various industries and scientific fields, allowing for precise temperature
measurement without direct contact with various materials.
Highly sensitive thermopile sensors also exhibit favorable qualities compared to alternative
temperature sensor modules in terms of ruggedness and reliability, making them well-suited
for demanding and routine applications.
This article will delve into the operational principles of thermopile detectors and the diverse
applications they find in numerous industries.
Image Credit: Ivan Smuk/Shutterstock.com
What is the Working Principle of a Thermopile
Detector?
Understanding thermopile detectors necessitates a basic comprehension of thermocouple
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technology. Thermocouples, the most common type of electrical temperature-sensing
components, consist of two distinct metal wires joined to form a "hot junction" and a "cold
junction."
When the joint is heated or cooled, it generates a subtle voltage (V), also known as the
Seebeck voltage, corresponding to temperature changes.
Although there is a proportionality factor to consider, for this article, it suffices to know that
the voltage generated is directly linked to temperature differences between the hot and cold
junctions.
Thermopile detectors encompass an array of thermocouples interconnected in a series.
The fundamental concept is to amplify the impact of each element.
They can be likened to a cluster of miniature thermocouple junctions, similarly separated
into hot and cold junctions consisting of alternating n-type and p-type materials, commonly
referred to as "arms."
The specific materials used in the arms can vary between different thermopile types. For
example, thin film systems often employ antimony and bismuth arms, whereas silicon
thermopiles feature alternating n-type and p-type Poly-Silicon or n-type and Gold or
Aluminum.
The cold junctions are usually linked to the detector package and positioned around the
periphery, while the hot junctions, defining the active area, are situated at the center and
coated with an energy absorber.
These hot junctions are suspended on a thin membrane to thermally isolate them from the
remainder of the package.
The multiple thermocouples within a thermopile detector are connected in series. This
implies that the voltage difference generated by each thermocouple is combined to produce
a total voltage output. This total voltage output is directly proportional to the temperature of
the measured object.
Given that the Seebeck effect generates a relatively weak signal, thermopile detectors are
equipped with voltage amplifiers to ensure the signal's readability by a meter or data
acquisition (DAQ) system. Subsequently, a calibration factor or transfer function is applied
to convert the signal into a readable temperature measurement.
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Applications of Thermopile Detectors
Thermopile detectors have a wide range of applications across various industries due to
their precision, stability, and durability. The critical applications of thermopile detectors
encompass:
Energy: Thermopile detectors serve in temperature control for boilers and heating
systems, as well as in solar panels to monitor panel temperature, ensuring optimal
efficiency.
Automotive: These detectors find use in temperature sensing for engines, exhaust
systems, and catalytic converters, along with temperature monitoring in electric
vehicle battery packs.
Aerospace: In the aerospace sector, thermopile detectors play a role in temperature
monitoring for spacecraft and satellites, and they are essential for temperature control
in aircraft engines.
Medical: Within the medical field, thermopile detectors contribute to temperature
measurement in equipment like infrared thermometers and enable non-invasive body
temperature monitoring, such as fever detection.
Industrial: Thermopile detectors are integral for temperature control and monitoring
in various industrial processes, including drying, baking, and heat treating, as well as
in industrial ovens and furnaces.
Looking for Thermopile Detectors?
Dexter Research Center provides infrared sensing solutions for diverse detection needs. To
learn more about thermopile detectors, users can refer to the technical papers section on
the M5 Thin Film-based thermopile detector product page for a comprehensive introduction
to Thermopile Detectors.
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ermopile Detectors for Gas
Measurement and Analysis
Thermopile infrared gas detectors have many applications, from providing early
warning systems for trace levels of atmospheric gases to analyzing several gases in
an anesthetized patient in the operating room.
Dexter Research Center has a range of highly versatile thermopile detectors developed
over forty years that can be custom-designed for each specific application. Thermopile
detectors are passive radiation sensing voltage-generating devices, which require no bias
or cooling and do not emit any radiation.
Thermopile Infrared Gas Sensors
Infrared (IR) gas detection is a well-established sensing technology. When exposed to
infrared light, gas molecules absorb some of its energy and vibrate more vigorously:
different gases absorb IR at specific frequencies. The amount of energy absorbed is related
to the concentration of the gas, and results in a rise in temperature: the temperature
increases in proportion to the concentration of gas present.
A thermopile converts this heat into electrical energy, generating an output voltage which
offers information on the levels of gas or gases present. A thermopile is a range of miniature
thermocouple junctions connected in series as differential pairs. These differential pairs
consist of hot and cold junctions connected by alternating materials called arms, creating a
Seebeck effect - where a temperature difference between two dissimilar electrical
conductors or semiconductors produces a voltage difference - between the junctions. The
voltage produced is proportional to the temperature gradient between the hot and cold
junctions.
A Dexter IR gas detector is sensitive to changes in temperature as small as 0.1 °C and can
operate between -40 °C to 85 °C without being affected by ambient temperature
fluctuations.
Advantages of Thermopile IR Gas Detectors
In IR instruments, only the sample cell and related components are directly exposed to the
gas sample stream: gases of interest, including carbon monoxide, carbon dioxide, methane
hydrocarbons and refrigerants, are often corrosive and reactive.
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In other types of sensor, such as those based on semiconductors, oxidation and catalytic
technologies, the sensor itself is directly exposed to the gas, causing the sensor to stop
working properly or fail entirely.
IR thermopile gas detectors are sealed against corrosion, making them robust, reliable,
stable and long-lasting. And the remain active without a battery or external power source.
Dexter’s Design Capabilities
Dexter boasts a family of 20 models of thermopile and over 1,000 individual parts meaning
they can be quickly customized based on customer’s specific application requirement,
whether the quantity is one or one million.
Dexter’s detectors are designed in small transistor-type packages and before each package
is hermetically sealed, air is removed and the package is backfilled with one of four gases
(argon, nitrogen, xenon or neon). This provides one of the key thermal paths for energy loss
from the active area and affects four important performance parameters: the output voltage,
responsivity, signal-to-noise ratio (a measure of signal strength relative to background
noise) and time constant (how quickly charge falls in a circuit). Different backfill gases have
different molecular thermal conductivity, and this property affects the thermal resistance of
the detector and package, which affects the output voltage, responsivity and time constant.
Dexter’s four standard gas options have varying effects depending on the type of
thermopile.
Dexter offers two distinct types of thermopile detectors with different performance
characteristics: thin film-based (based on antimony and bismuth) and silicon-based (poly-
silicon or silicon combined with gold or aluminum). Thin film-based thermopiles provide a
higher signal-to-noise ratio than silicon-based thermopiles but will have a slower time
constant than a silicon-based thermopile with equal output and are available with larger
active areas. Silicon models are cheaper, and operate at higher temperatures of 125 °C
compared to thin film models, which work best around 100 °C although some silicon
models can be configured to work at 225 °C.
Dexter’s IR gas sensors can be used in a wide variety of applications, from continuously
monitoring combustible, flammable and toxic gases, as well as falling oxygen levels, often
as part of a safety system. They can be used as fixed ‘open-path’ gas detectors which send
out a beam of infrared light, detecting gas anywhere along the path of the beam - widely
used in the petroleum and petrochemical industries to detect leaks of flammable gases.
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Detectors can also be portable and handheld, for example blood alcohol breathalyzers.
Detectors can also be used to perform sophisticated gas analysis to monitor the critical
levels of gases exhaled by a hospital patient under general anesthetic, or premature babies
in incubators for example.
References and Further Reading
1. What are IR gas detectors - Enggcyclopedia
2. Effects of encapsulation gas on thermopile detectors - http://dexterresearch.com/?
module=Page&sID=technical-library
3. Introduction to thermopile detectors - http://dexterresearch.com/?
module=Page&sID=technical-library and http://dexterresearch.com/?
module=Page&sID=gas-analysis
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About
About
Dexter Research offers 31 core thermopile
products, more than all global competitors
combined, each 100% tested for industry-
leading quality. We now provide our
customers with a choice from over 500
thermopile configurations, and we have new
thermopile detectors coming on-line and
new customers using our products around
the world.
Strategically and tactically, we’re in a great
business position, and we’re not done
improving our products and performance. In
particular, Dexter Research has responded to
our competitors with new aggressive
marketing and pricing strategies.
Dexter Research Center, Inc. was founded by
Robert Toth, Ph.D in 1977. A leading thin film
and materials expert, Bob believed then and
now that:
No other infrared device outperforms
a thermopile as an affordable
detector.
There is no substitute for
collaboration as a means to optimize
infrared detector performance,
packaging, reliability and durability to
surpass the current benchmarks and
beyond our customer expectations.
F I N D O U T M O R E

Dexter Research: An Introduction to Thermopile Detectors

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