Infrared radiation sensors

There is limited application for CO trim systems which are widely used on utility and other large water-tube boilers. The principle of operation is for an infrared beam to traverse the flue from emitter to sensor. The absorption of the infrared radiation is proportional to the CO content. 

Luminescence can be defined as the emission of light (intended in the broader sense of ultraviolet, visible, or near infrared radiation) by electronic excited states of atoms or molecules. Luminescence is an important phenomenon from a basic viewpoint (e.g., for monitoring excited state behavior) [1] as well as for applications (lasers, displays, sensors, etc.) [2,3]. 

The sensor unit of an IRET usually consists of an infrared sensor, in most cases a thermopile sensor in a TO-5 or TO-46 housing, a gold plated barrel, which reflects the infrared radiation from the ear to the sensor and reduces the sensitivity of the sensor to ambient temperature changes (see Fig. 3.43). 

A thermopile sensor generates an output voltage that depends on the temperature difference between its hot and cold contacts. For infrared temperature measurement, the hot contacts are normally thermally insulated and placed on a thin membrane, whereas the cold contacts are thermally connected to the metal housing. Infrared radiation, which is absorbed by the hot contacts of the thermopile, causes a temperature difference between hot and cold contacts. The resulting output voltage is a measure for the temperature difference between radiation source and cold contacts of the thermopile sensor. It is therefore necessary to measure also the temperature of the cold contacts by an additional ambient temperature sensor in order to determine the temperature of the radiation source. 

Infrared radiation has a very low energy and cannot eject electrons from most common photoemissive surfaces. The initial infrared sensors were temperature-sensing devices. Thermocouples and thermistors are forms of bolometers used for detecting infrared radiation. 

Type of Interior Sensor Passive infrared (PIR) Presently the most popular and cost-effective interior sensors. PIR detectors monitor infrared radiation (energy in the form of heat) and detect rapid changes in temperature within a protected area. Because infrared radiation is emitted by all living things, these types of sensors can be very effective. 

A fiber-optic device has been described that can monitor chlorinated hydrocarbons in water (Gobel et al. 1994). The sensor is based on the diffusion of chlorinated hydrocarbons into a polymeric layer surrounding a silver halide optical fiber through which is passed broad-band mid-infrared radiation. The chlorinated compounds concentrated in the polymer absorb some of the radiation that escapes the liber (evanescent wave) this technique is a variant of attenuated total reflection (ATR) spectroscopy. A LOD for chloroform was stated to be 5 mg/L (5 ppm). This sensor does not have a high degree of selectivity for chloroform over other chlorinated aliphatic hydrocarbons, but appears to be useful for continuous monitoring purposes. 

Because the spatial area with higher temperature on the catalyst surface of one of the samples of the library is very small the detection of catalytic activities through temperature measurement cannot be carried out by direct temperature measurements but only by non-contact methods such as pyrometry or IRT. The IR video camera used here measures the emission at every point of the library in parallel. The detector consists of a 256x256 pixel array of Pt-silicide-IR-sensors. Each pixel delivers a voltage-signal that depends on the infrared radiation and the sensitivity of that pixel (fixed pattern noise). 

The detector best suited to meet these conditions is a radiation type sensor. Ultraviolet (UV), infrared and visible radiation are generated when combustion produces a flame and all three types of radiation sensors respond to the radiation from the flame. 

Diamond-like carbon since its inception in 1962 has found applications in some very important areas. These applications include coatings used in scratch-resistant optics, razor blades, prosthesis in medical applications electron emission surfaces in electronics as an insulator material for copper heat sinks in semiconductors such as solar cells and sensors for visible to infrared radiations and as structural materials such as deuterated DLC film used for neutron storage in advanced research instrumentation. As technology matures the unique properties of DLC will find new and important applications. 

Thick oil on water absorbs infrared radiation from the sun and thus appears in infrared data as hot on a cold ocean surface. Unfortunately, many other false targets such as weeds, biogenic oils, debris, and oceanic and riverine fronts can interfere with oil detection. The advantage of infrared sensors over visual sensors is that they give information about relative thickness since only thicker slicks, probably greater than 100 pm, show up in the infrared. 

The most attractive sensors now being developed are the Fourier transform infrared spectrometer (FTIR) and the near-infrared (NIR) spectrometer for the on-line measurement of composition changes in complex media during cultivation. The FTIR measurements are based on the type and quantities of infrared radiation that a molecule absorbs. The NIR measurements are based on the absorption spectra following the multi-regression analyses. These sensors are not yet available for fermentation processes. 

By measuring the spectral distribution of the upwelling infrared radiation emitted by the Earth and its atmosphere, spaceborne sensors can provide information on the vertical temperature profile and on the atmospheric abundance of radiatively active trace gases. When local thermodynamic equilibrium conditions apply, the radiance received by a detector with spectral response function y> over frequency interval Av and viewing vertically downwards is given by (see Eq. 4.69a)... 

There are a few common methods of measuring oxygen concentration in the gas phase. Electrochemical sensors and paramagnetic sensors are typically used to measure oxygen concentration on a wet and dry basis, respectively. Carbon monoxide (CO) is most commonly measured using a nondispersive infrared technique. A gas sample flows between an infrared radiation source and an infrared detector. Carbon monoxide absorbs infrared radiation, hence the difference in intensity proportional to the concentration of CO in the gas sample. 

For measurements in the gas phase, sensors based on absorption of infrared radiation by CO2 molecules are preferred. 

The elements of an infrared melt temperature sensor are a sapphire window, an optical fiber, and a radiation sensor with associated signal-conditioning electronics as shown in Fig. 4.17. IR melt temperature probes are commercially available [85, 86] and fit in standard pressure transducer mounting holes. Because the sapphire window is flush with the barrel or die, the sensor does not protrude into the polymer melt. As a result, the sensor is less susceptible to damage, there is no chance of dead spots behind the sensor, and the melt velocities are not altered around the sensor. When melt velocities are changed, the melt temperatures will change as well. Therefore, the melt temperatures measured with an IR sensor are less affected by the actual measurement than with an immersion sensor. 

Various types of radiation are used a-rays, p-rays, y-rays. X-rays, and infrared radiation. A continuous stream of radiation is emitted from a constant radiation source (X-ray tube or radioisotope), passes through the material whose thickness is being measured, and strikes the radiation sensor. As radiation passes through the extrudate, some of the radiation is absorbed and, as a result, the radiation reaching the sensor is less intense. The amount of absorption depends on the material s density and thickness. If the density is constant, the amount of radiation absorption is a direct measure of thickness. 

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