Types of Infrared Detectors

Infrared Absorption Detectors. Two types of infrared detectors have been offered commercially. The first is a filter instrument similar in design to that shown in Figure 16-13. The second, and more sophisticated, type of infrared detector is based on Fourier transform instruments similar to those discussed in Section I6B-1. Several of the manufacturers of Fourier transform infrared (FTIR) instruments offer accessories that permit their use as HPLC detectors. Infrared detector cells are similar in construction to those used with ultraviolet radiation except that windows arc constructed of sodium chloride or calcium fluoride. Cell path lengths range from 0.2 to 1.0 mm and volumes from 1.5 to 10 pL. 

The volume opens with a broad-brush introduction to the various types of infrared detectors that have evolved since Sir William Herschel s discovery of infrared radiation 175 years ago. The second chapter presents an overall perspective of the infrared detector art and serves as the cohesive cement for the more in-depth presentation of subsequent chapters. Those detector types which, for one reason or other have not attained wide use today, are also discussed in Chapter 2. 

Numerous physical mechanisms are usable for detection of infrared radiation, and thus there are numerous different detectors. This section lists some more important types of infrared detectors. The key for the presented classification is the basic effect used for the detection of IR radiation. 

Finally, as an illustration, a frequency dependence of the specific detectivity-bandwidth product for two different types of infrared detectors is given, one of them photonic and the other thermal device. One of the detectors is a HgCdTe... 

Photodetector (photon detector) - A type of infrared detector that has fast response, (on the order of microseconds) limited spectral response and usually requires cooled operation photodetectors are used in infrared radiation thermometers, scanners and imagers. 

As in all Fourier transform methods in spectroscopy, the FTIR spectrometer benefits greatly from the multiplex, or Fellgett, advantage of detecting a broad band of radiation (a wide wavenumber range) all the time. By comparison, a spectrometer that disperses the radiation with a prism or diffraction grating detects, at any instant, only that narrow band of radiation that the orientation of the prism or grating allows to fall on the detector, as in the type of infrared spectrometer described in Section 3.6. 

Determination of the average chemical composition and polymer composition by size-exclusion chromatography (SEC) has been reported in the literature. Two different types of concentration detector or two different absorption wavelengths of an ultraviolet or an infrared detectors are employed the composition at each retention volume is calculated by measuring peak responses at the identical retention points of the two chromatograms. 

As shown in Table 25-2 (p. 761), four types of thermal detectors are used for infrared spectroscopy. The most widely used is a tiny thermocouple or a group of thermocouples called a thermopile. These devices consist of one or more pairs of dissimilar metal junctions that develop a potential difference when their temperatures differ. The magnitude of the potential depends on the temperature difference. 

Several types of GC detectors, such as infrared (IR), flame photometric (FPD), and electron capture 90,98,122,123 ggjj applied to the GC analysis of phthalates in... 

There are three types of thermal detectors the thermocouple, the bolometer, and the Golay detector. The thermocouple, the most widely used infrared detector. 

Although not specifically delineated, the volume is also divided into three general sections. The first addresses the full spectrum of infrared detectors and contains a limited coverage of all the material presented in subsequent chapters. It serves as an introduction to the volume and presents to the reader an overall view of the present state of the infrared technology art. It also serves as the mortar between the more in-depth discussions which follow. The midsection. Chapters 3,4, and 5, is a detailed analysis of those detector types which are most widely used today thermal, photoconductive/photovoltaic and photoemissive. 

The topics included here are limited to the usual types of noise in the common types of infrared photon detectors. Noise in thermal detectors, such as temperature noise in bolometers, is not included. Noise associated with the avalanche process is omitted. The detailed noise theory of phototransistors, an extension of shot noise in photodiodes, is not included. Modulation noise, an example of which arises from conductivity modulation by means of carrier trapping in slow surface states, is not included. Pattern noise, due to the... 

The first type of semiconductor bolometer to come into use was the thermistor developed during World War II at Bell Laboratories to provide a simple, reliable but sensitive detector for use both in the then rapidly developing science of infrared spectroscopy and for heat sensing applications. The thermistor bolometer is still one of the most widely used of infrared detectors, although it has been replaced by more sensitive devices for the more demanding applications. 

Instrumentation. Almost every imaginable type of gas detector or analyzer has been utilized in EGA, including hygrometers, nondispersive infrared analyzers, and gas chromatographs. Absorption of the products into solution permits analysis by coulometry, colorimetry, ion selective electrode measurements, or titrimetry. The most important analyzers are Fourier transform infrared (FTIR) spectrometers and, preeminently, mass spectrometers [19J. The two latter methods can be used to record spectra repetitively, thereby producing a lime-dependent record of the composition of the gas phase, from which EGA curves can be constructed for selected species. 

There are two basic types of photon detectors photoemissive and solid state. The photoemissive type is generally represented by the photomultiplier tube detectors, whereas the solid-state type detectors are represented by photodiode detectors, pyroelectric detectors, and infrared detectors. 

Receiving equipment for aircraft astrophysical investigations in the far infrared has been developed and flown in 1974-1975 on board the AN-30 aircraft. Four types of infrared and submillimeter detectors mainly of photoresistor type are used in the wavelength region from 10 mkm to 1 mm. Thermal background at the detectors is limited by cooled bandpass filters and by optimal matching of the detectors with the telescope optics. The spectral filters used are combinations of quasiresonance metal mesh filters of different structure and Q-factor from 2 to 7 with the Yamada cut-off powder filters. A tunable Fabry-Perot interferometer, a polarimeter for linear polarization measurements and an aircraft 25 cm-telescope are briefly described. 

There are four basic types of flame detectors (1) infrared, (2) ultraviolet, (3) photoelectric, and (4) flame flicker. 

While heat may indicate that a fire is in progress, often monitoring this one parameter is not sufficient to insure fire safety, since localized fires may not excite the heat sensor. Instrumentation is available to monitor the cylinder cabinet for smoke, ultraviolet, or infrared radiation. Use of multiple types of fire detectors provides the most protection in all types of situations. 

There are two basic types of beam detectors, both of which operate on the principle of light obscuration an infrared beam is projected across the area to be protected and is monitored for obscuration due to smoke. If smoke is present in the beam, usually for a period of 8-1 Os, a fire alarm indication is activated. There are two basic types. 

There are a number of parameters quoted in literature as figures of merit of infrared photodetectors. The use of these parameters is dependent on a certain degree on the particular type of the detector. 

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