Technical Library

Application Briefs

Introduction to Thermopile Detectors
The basic principles and nomenclature of thermopile detectors are explained. There is also an explanation of the types of thermopile detectors available from Dexter Research, as well as an abbreviated list of the ever-growing applications for thermopile detectors. Download PDF.

Infrared Radiation and Radiometry Introduction
In this brief we discuss how an object's temperature affects the peak emitted spectral wavelength according to Wien's Displacement Law.  Several spectral curves are included to illustrate.  Download PDF.

Emissivity Correction for a Radiometer
The optical power emitted by a target will depend on its emissivity and temperature. A simple technique to take into account the change in sensitivity is described. Download PDF.

A Simple DC Radiometer
This brief explains the basic principles of remote temperature measurement using thermopiles. Download PDF.

Temperature Compensation of a DC Radiometer
Since a thermopile is an array of thermocouples, the temperature of the cold junction of the thermocouple must be known to provide an accurate temperature measurement. This brief describes a method for dealing with a variation in the cold junction temperature. Download PDF.

Variations in Calibrations of Radiometers Using Cut-on Optical Filters
The amount of optical energy falling on the thermopile will depend on the transmission characteristic of the filters used as the window in the detector. This brief discusses the effect of the variation in the bandwidth of the filter in the calibration of a radiometer. Download PDF.

Effects of Encapsulation Gas on Thermopile Detectors
Most thermopiles are hermetically sealed with an inert gas in the package at one atmosphere pressure. The selection of encapsulating ga allows customization of detector output sensitivity and time constant without affecting other parameters such as resistance or noise. Download PDF.

Thermopile Configuration Options

Thermopile Detector Comparison: Thin Film vs. Silicon
Typical amplifier circuits for use with thermopile detectors are shown. Download PDF. See also: Example Amplifier Circuits (PDF).

Thermistor Options
Dexter Research offers several thermistor options for thermopile detectors.  This document gives resistance vs. temperature plots and tables for internally mounted Chip Thermistors, Poly-silicon Resistors on ST60 & ST150 models and Chip-in-Glass thermistors for external use.  Download PDF.

Aperture Options
The field of view (FOV) may be modified inside the detector package using apertures. This is also useful in eliminating crosstalk in multi-channel detectors. On TO-5 packages, the FOV may be modified by customizing the internal aperture hole size. This also defines the amount of energy coming into the package and subsequently falling on the detector active area. Download PDF.

Standard Windows and Filters
Standard optical filters, wide-band and uncoated, are compared in an informative table. Download PDF.

Typical Spectral Characteristics
Typical spectral characteristics of select optical windows (wide-band pass) are graphed in transmission curves for select filters. Download PDF.

Diffractive Silicon Lens
As a window option for our ST line of thermopile detectors, we offer a Silicon Diffractive Lens.  This documen includes technical information such as diffractive lens transmission curve, lens dimensions and example FOV when used with our model ST60 thermopile with 0.61mm active area.  Download PDF.

Technical Background

Thermopile Time Constant Determination
The methods for measuring the time constant of a thermopile are discussed.  Download PDF.

Detector Normalized Angular Response
The normalized angular response for a thermopile detector is shown. Download PDF.

Detector Normalized Response as a Function of Frequency
The frequency response of thin film and silicon-based thermopiles are shown for sinusoidally modulate radiation. Download PDF. 

Blackbody Spectral Radiance
Calculation of the blackbody radiance for three spectral regions of commonly used filters is given. Download PDF.

Detector Signal Calculation
The calculation of a detector signal in a reflective optical system is shown. Download PDF.


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